Caravan PSU / Battery Charger issue

[Another Dave]

I posted about this last year and have only just been able to remove it to investigate further.

My caravan has a built in PSU/Charger for the 12v 100aH leisure battery. Whilst on the mains supply
it should keep the battery topped up but i was experiencing the battery voltage fluctuating between
11 and 14 volts.

This has happened to several batteries so i know its the charger and not the batteries, in my previous
someone mentioned a " ferroresonant transformer charger ". Never heard of this and had to look it up.

I was expecting there to be something in it other than this....

[Another Dave]

The red/yellow wires are both 12v positive outputs, the earth is through the case and it uses
a little bracket to give multiple earths on the connector block.  Forward thinking from the designers
i guess.  Turn the earth to a + by snipping the earthing pin.

In use the battery voltage was dropping well below 12v even with a known good battery and very
little current draw, lighting is mostly LED's and the only other item powered is a small water
pump used for a few seconds at a time. Everything else is mains powered.

I have tried it briefly here for a few hours and the voltage varied between 14.5 and 15v open circuit. It
did drop and climb over a few hours. Putting it under load may aggravate that?

Quick look at the parts because im not touching that cap after having it powered,  it looks like it may hurt.    
One bridge rectifier and one 33000uF capacitor.

There is something attached to the side of the transformer, i initially thought a temperature sensor but
after reading the old thread it maybe a capacitor? 

(Seekonk..    they usually have about a 4-10uF 400V capacitor on the resonant winding )

Possibly that?



My numpty know nothing status still applies so please be gentle 

Thanks.

[richard.cs]

I don't think it's a ferroresonant design, it's just a crude charger with no voltage regulation at all. Still,  if it delivers 15V under no load I'd expect it to charge a battery OK (with risk of overcharging if used long term). It can only be that either you're drawing more current than you think or there's a dodgy connection inside that means the voltage collapses with even small loads. The thing on the side of the transformer will be a thermal switch that disconnects the power when the transformer gets too hot due to overload (as will probably happen if you connect a dead flat battery).

Measure the output voltage with a couple of 12V car bulbs connected (ideally try a few different loads) and let us know what it is. It's surely possible to get it working but any case it's a bit of a crap design.

[SeanB]

Very likely the bridge rectifier is open circuit or high resistance on at least 1 diode, so that would make it a half wave rectifier. Does anything get hot when under no load ( the toriod should stay cool, if not it is toast) and when you connect the battery. Check the wires to the scew terminals, I often have seen that they either beeak there inside the plastic or the small holding screw is loose or stripped, or the thin brass tube cracks.

[tautech]

In use the battery voltage was dropping well below 12v even with a known good battery and very
little current draw, lighting is mostly LED's and the only other item powered is a small water
pump used for a few seconds at a time. Everything else is mains powered.

That's not right and as Sean points out a faulty bridge is the most likely suspect.
From what I see in your pic this is the schematic:



Simple as it is there are 5 things to check:

Fuses
Transformer primary side resistance (not OC)
Transformer secondary side resistance (not OC)
Transformer secondary no load voltage
Diode bridge (DMM diode test)

Working correctly and connected to a charged battery I'd want to see ~ 14.5V max @ the battery.

[GEuser]

Personally speaking , now that you have that out either chuck it in the bin or use it for something else but anything not to do with battery's .

If battery's like the 100ah you mentioned are cheap over there then ignore the above , as fairly inexpensive Float chargers or trickle/float chargers are around and at a decent amperage out amount i'd go for one of those , look up Float chargers ..imo

[Martini]

Working correctly and connected to a charged battery I'd want to see ~ 14.5V max @ the battery.

If it's meant to be constantly on, you end a up the trickle charging zone and I believe it should be under 14 V (I'd say 13.8 V but it might varies with ambient temperature).


If I were the OP, I'd probably consider changing the charger for a smarter one to preserve battery life. If current consumption is low, a charger will be considerably cheaper than one 100 Ah battery, so...

[GEuser]

The old Farmer next door (5K's out rural here) had a charger on his kitchen table just the other week , he had one end pulled off trying to see why it would not work .

Anyway i brought it back here and pulled it to bits , all that happened was a bug had decided to walk across the 350Vdc tracks (a switch-mode) and got vaporized and blew the solder on pcb fuse .

Anyway again , i was really surprised with that charger , i forget the brand but a 30amp out and did everything! , it checked the battery whether gel/calcium/acid and another i forget , did a load test , de-sulfates and then reconditions (all if needs to happen) automatically , then sits on Float after it does its thing , actually i wanted it but he is a good neighbor and i was not prepared to hit him with a cricket bat  , i think it might have been a Repco brand (a auto store) but i'm not sure ... it was really wizz bang .

edited>duh  i forgot to mention the reason i was posting , 15 or 16v to de-sulfate for around 5 minutes , a test load of 6 or so amp , the recondition cycle never started but i think it loaded the battery down to a predefined voltage then started all over again , Float was a pulsing voltage hanging around 13.8v +.5v .

[madires]

I'd also recycle the old charger for something else and go for a proper charger, i.e. a charger with a controller monitoring the voltage and switching to float/maintenance mode. A sealed switch-mode based smart charger with 5A output costs about 50 bucks. And add a switch between charger and battery to prevent the charger draining the battery when not connected to mains, in case it's necessary.

[Martini]

Forgot to say but my inverter does all that and takes care of the switching between mains and battery power.

[Another Dave]

Thanks guys, it should be putting out a stable 13.8 volts to prevent the battery gassing off too much and
boiling the battery dry.

Its a 6Amp continuous charger with an 8A max output.   Drawing way less than the 6amps continuously
and possibly only exceeding that very briefly when the waterpump activates which is usually only
a few seconds whilst filling a kettle or the small hand basin.

Not tested the charger attached to a battery, i will do that next and post back my findings.  Not a fuse
both the mains and 12v fuses are fine.  Open circuit load = 15v which is rather high i think.

Bridge rectifier will be cheap to replace, but the 33,000uF capacitor seems to be quite expensive
and i prefer the idea of replacing the unit with a better one rather than waste £15.

If i can repair this cheaply then i would like to though.  I will see if i can find more info on the charger
but i think its just a basic one that should give 13.8v. I know it can be used as a PSU with no
battery connected also.

Anyone from the UK bought a charger recently that may suit my needs?

Thanks..

[Martini]

Supplying 13.8V to a discharged battery is too much anyway to maximize its life expectancy (too high a current).
I reckon you're better off with a smart modern charger. You could even use a relay to bypass the inverter when plugged to the main, thus you could draw as much power as you'd like rather than being limited by the charging rate.

[Another Dave]

The battery should never be discharged though. Its always kept at home and topped up monthly,
occasionally i use it to power something to drop the voltage a little bit and then leave it on
charge a small CTEK charger 3.6amp max? Thats designed to be left on 24/7.

In the caravan the battery is only there to stabilise the voltage and a backup if the main
power fails. Previously the battery was used to power the electric motors to move the
caravan, so a small discharge before actually using it.

But we swapped storage yards and can now reverse upto the caravan.

It starts with a fully charged battery and during the day we are mostly out so no 12v draw at all
and just the lights and waterpump later on and in the morning.  Nowhere near enough power
to drain the battery. It does take a day or so for the voltage to drop.

I had the same battery attached to an inverter and running a 100w bulb for over 4 hours and
the voltage was still at 12.2v.  So the battery is good and we do not draw that amount
of power in a 24hr period.

I think the charger maybe actually draining the battery also.

I have several chargers that can be used in its place, either wired in 24/7 or used on a plug as
and when needed.

Going to wire it upto a battery now and see if it draws power.

Thanks. 

PS.. even if i dont re-use it i would like to know what to look for and have a play with it. Eager to learn

[tautech]

Thanks guys, it should be putting out a stable 13.8 volts to prevent the battery gassing off too much and
boiling the battery dry.

You're a bit light there^^^ old style auto regulators were set in the 13.8-14.2V range.
Anything ~15+ V does gass lead acid batteries, however this was sometimes used as a maintenance charge to combat sulfation.

But this overlooks new LA auto battery technologies, some of which can be floated as high as 14.5V.
Deep cycle storage is the type best used for caravans.

Anyone from the UK bought a charger recently that may suit my needs?

The battery should never be discharged though. Its always kept at home and topped up monthly,
occasionally i use it to power something to drop the voltage a little bit and then leave it on
charge a small CTEK charger 3.6amp max? Thats designed to be left on 24/7.

A bigger one of those^^^^^ 

[Another Dave]

Connected upto my 100Ah leisure battery, Ive had a small sub 2amp load on it for a couple of hours.
Voltage at 12.64.  Connected the charger up and it jumped to 12.9 volts at 0.7amps charge.

After a few minutes the voltage increased to 13.2 and the charge rate dropped to 0.5amps.

I will give it a few hours and see what happens to the voltage.  Currently no load on the battery which
is how it would be during the daytime whilst we are out and about. No draw from teh battery.

No diode between the 33,000 uF capacitor and the battery so the battery charges the capacitor.

[Martini]

The inverter is off during the day as well?

[Another Dave]

No inverter in use in the caravan, i only used that at home to test the batteries and they held up
well over 4 hours with a 100Watt bulb on an inverter which i think drew closer to 140watts from the
battery.  I found the 600watt inverter used more power than the 300watt one for the same load.

So no inverter.  In the caravan its just the battery with the charger from a mains lead and LED lighting
and the waterpump.  Nothing else draws any load.


I connected the battery last night and the results..

22:00   13.5v    0.35A
23:00   13.7v    0.36A
00:00   13.8v    0.36A
02:30   14.0v    0.34A
13:00   14.2v    0.35A    All good it seems...

Until i add some load.  I put a 12v LED wand that draws approx 0.75A, Voltage dropped down to
13.7v and the chargers output went upto 0.6A.  Voltage dropped to 13.6v so i added more load.

I added the 600w inverter with a 10w small radio/cassette player. This showed a 0.75A draw from the
inverter cable.  Voltage dropped to 13.4.
I have now added 2 x 15w bulbs onto the inverter also and the voltage dropped to 12.7v.

Yet the chargers amperage has not yet gone above 0.6A.

Currently still on 12.7v and pulling approx 4amps but the charger is at 0.6A still. Because the battery
is good i expect it to take a while to drop the voltage further. I did expect the amperage to increase by
now. Maybe the voltage is not low enough yet?

12.7volts is not right though is it?  Dumb charger should be putting out 13.8v (ish) until it maxes out
at its 6amp output?

No seeing the voltage spikes that i was getting last time we used it, maybe the 0.6 amp is all its going to
output?

[tautech]

Yeah, it doesn't look right. 

Which charger are we looking at ATM ? 

Can you trust your DMM ?

[jitter]

I don't really trust that charge curve.
Normally, a lead acid battery needs a constant voltage charge and the current drawn mainly depends on the state of charge of the battery.
A really flat battery will try to charge at a higher current than the charger can deliver, so voltage will be lower than the nominal charge voltage until the current tapers off.

I have more experience with SLA and SLI batteries than deep cycle batteries, but maybe you need to discharge that battery somewhat deeper and see if the charge current increases. If it charges all the time at ~350 mA, even with a flat battery and a charger rated at 6 A, I think it's pretty sure it's not working like it should.

[Delta]

That is NOT a charger, it's an UNREGULATED power supply!  The voltage will wander all over the shop depending on load.

My guess would be that the big electrolytic cap has gone bad and has rather high leakage, draining your battery when connected.

Connect a battery to the "charger" without the mains connected and measure any current drawn from the battery.

You should be able to remove the cap entirely and that thing will still charge a battery.

[tautech]

You should be able to remove the cap entirely and that thing will still charge a battery.

Quite true 
That's how old dumb chargers were made, NO smoothing cap.

[jitter]

That is NOT a charger, it's an UNREGULATED power supply!  The voltage will wander all over the shop depending on load.

You would be inclined to think so, but actually, no, it is mainly determined by state of charge of the connected battery, it is by far the strongest of the two (read: lowest internal impedance). And since the output is a mere 5% of the input a few V mains wandering doesn't really do that much on the secondary side.
And yes, a flat battery will pull the voltage of the charger way down at first, but that happens to regulated chargers a well.

My guess would be that the big electrolytic cap has gone bad and has rather high leakage, draining your battery when connected.

Connect a battery to the "charger" without the mains connected and measure any current drawn from the battery.

Good tip.

You should be able to remove the cap entirely and that thing will still charge a battery.

Indeed. I have a 12 V, 6 A charger from Absaar which doesn't even have a cap on the output, and car batteries don't mind this at all. I know it wouldn't be too wise on SLAs which seem a bit more sensitive to ripple. Don't know for sure about deep cycle batteries, though.

I think I would prefer a more modern uP controlled charger that can keep the battery charged without risk of overcharging.

[Another Dave]

OK whats the punishment for making a STUPID!!! mistake?   

Test meter is one of those cheapo yellow things, running across the 10Amp unfused side. I expected it
to go bad so didnt risk my better meter which you may think is crap also 

I used some test leads with small croc clips on them, and when connecting 2 other old style chargers the
amperage never rose above 0.75A.
Silly me for using CRAP!!!  leads....

I even ran the battery down to 11v and the inverter started to beep with no increase in current from the
chargers. Connected with the proper leads and 4amps + was seen. Guessing the leads for that are also
not upto the job.

I knew i should have used my 60A wattmeter but too lazy to go and find the correct terminals i fitted to it.

Battery on charge again, connected directly and start again tomorrow or friday.

Whats my punishment???   



(Sheepish)   Thanks.

[tautech]

A good whipping with those shitty DMM leads. 

Most of us have been caught out like that. 

[jitter]

OK whats the punishment for making a STUPID!!! mistake?   

Test meter is one of those cheapo yellow things, running across the 10Amp unfused side. I expected it
to go bad so didnt risk my better meter which you may think is crap also 

I used some test leads with small croc clips on them, and when connecting 2 other old style chargers the
amperage never rose above 0.75A.
Silly me for using CRAP!!!  leads....

I even ran the battery down to 11v and the inverter started to beep with no increase in current from the
chargers. Connected with the proper leads and 4amps + was seen. Guessing the leads for that are also
not upto the job.

I knew i should have used my 60A wattmeter but too lazy to go and find the correct terminals i fitted to it.

Battery on charge again, connected directly and start again tomorrow or friday.

Whats my punishment???   



(Sheepish)   Thanks.

Well, seems like you learned this lesson the hard way:



At least you had the sense to try a different meter before condemning a possibly correctly working charger.

When you know a thing or two more tomorrow, I'm interested to know what the voltage is that this charger tops out on when the battery is full. Also if it's sized properly to maintain a trickle charge, or if this is one of those things - like my Absaar - that you just don't leave connected indefinitely.

Does your battery come with charging data (possibly printed on the side)?

[Another Dave]

No charging data on the battery, i think im fighting a loser here..  Comparing the charger to a 6amp and 8amp
chargers that are probably as old as the caravan charger.

I used a 100A watt meter and 14awg cable thats approx 18" long.  Dropped the battery down to 12.1 volts under
a 3.8 amp load.  Connected the caravan charger and its barely over 1amp and drops quite quickly, but the voltage is
only around 13.3v.

I connected the 8amp charger and the amperage went over 4amps on the watt meter but the chargers LEDs showed
a max 8amps charge. (but its probably 20 years old and a similar design to the caravan charger. Voltage held at
slightly over 14v with the 8A charger though.

Pride says i want to fix it, but my pocket says give up and buy a new charger.

Thanks to Dave and this site i have fixed several TV's and now the readout on my lathe   

That feeling of i fixed something is great.  No sob story but my health has suffered and i cannot do a lot
of stuff that i used to  (lorry driver / mechanic).   

Thanks 

[tautech]

Just wondering if the old charger was well matched BUT you have low voltage mains supply. 

That might explain the low charging rates.

Do you have a light gauge supply to the caravan and/or have low mains voltages locally.
Do you feel comfortable checking the mains voltages?

[jitter]

Maybe the caravan charger isn't faulty after all.

From SLAs (Sealed Lead Acid) batteries I know that there are two sorts of usage. One is standby usage in which a charger is always maintaining the charge level to keep the battery ready for action (think e.g. of a UPS). The other is cycle use in which a large chunk of the charge is used up before charging takes place.
The former uses a lower level, say 13.8 V than the latter, which may be 14.4 V.

It may just be that the caravan charger is the standby type which charges at a lower max voltage that won't harm the battery when it stays connected for long periods of time.

Perhaps you can charge it as far as possible with the caravan charger and then have it tested by a pro. They should have a device that can assess the condition of the battery.

I'm also thinking about the mains voltage. If this is an old caravan that was made in the time when the UK (officially) still had 240 V mains, then maybe if your mains has been harmonized to the rest of Europe (i.e. dropped to 230 V), its output might be a little too low now (about 0.5 V).
I know that the UK may not actually have dropped from 240 V to 230 V as 240 V is still within tolerances, but who knows. We really did go from 220 V to 230 V.

[Delta]

I'm also thinking about the mains voltage. If this is an old caravan that was made in the time when the UK (officially) still had 240 V mains, then maybe if your mains has been harmonized to the rest of Europe (i.e. dropped to 230 V), its output might be a little too low now (about 0.5 V).
I know that the UK may not actually have dropped from 240 V to 230 V as 240 V is still within tolerances, but who knows. We really did go from 220 V to 230 V.

We didn't change anything!  Not a single transformer tap or voltage regulator was changed, we are still 240V!  (It was a political masterstroke - yeah yeah, we'll go to 230, but we want asymmetric tolerances.  So instead of 240 +/- 6% we "changed" to 230 -6 / +10% Do the maths...    I think some 220 countries also "changed" to 230 -10 / +6% )

Dave, please can you be a bit clearer in your posts, where exactly are you measuring these currents and voltages you are mentioning? 

[Another Dave]

Battery is 100% fine. I can run it for over 4 hours with a 100w load and it still held 12.2 volts.

Just had a week away with the van and the small CTEK 3600 charger (3.6 amps max) No issues at
all.  The charger was left switched off most of the time.  The charger was also using the solar connection
point which has a 20ft length of cable to that battery.  I have a twin battery setup when using panels.
This doesnt affect the issue with the original charger, unrelated.

The charger would get a bit warm with several lights on at the same time, but it didnt take long
for the full battery light to come on after switching the lights off.  So even with several lights on
for a few hours its probably pulling about 4 amps in the caravan. During the day nothing will
be drawn from the battery.


Delta, sorry if i confused matters. But i do seem to have had a good tinker.

At home i have the charger connected to a leisure battery. To drain the battery i connect a 240v 60w bulb
through a 600w inverter and measuring the voltage at the battery terminals and the current drawn by the inverter.
Inverter is actually pulling around 100w with the single bulb.  Inverter is only my home test setup to drain/put a load
on the battery Not used in the caravan.

I used a watt meter or clamp meter to test the power drawn by the inverter.

The original chargers voltage is tested right at the charger and at the battery terminal also. But i seem to have an issue
with the el.cheapo leads with croc clips. Either my old chargers are showing themselves as putting out 6 and 8 amps but
really only putting out 3 amps or my leads are total crap? 

I need to repeat the tests with decent and very short cables. I may have done that before we left but i  have forgotten....

So the battery is fine and the caravan is fine. I have a meter that shows the mains voltage and current consumption of
a mains powered item also.

[GEuser]

Sounds all good Another Dave , what is those (i assume a deep cycle) battery's worth over there , they can be expensive over here .

Those 12v Fluoro bar lights lights are good and put out a decent light and consume a miserable amount (like 150ma) , one can get 1 or 2 bar (tube) and from 6" to a foot long , very economical .

See when you mention a Leisure battery any battery can be that , it would be better to categorize the type ie> gel , deep cycle , calcium , acid excetera .

I ran a thick lead via a 100a relay from the alternator through a plug to the battery in the van for the Fridge , a switch and voltage meter on the Dash , in gas mode sitting on 120k or more for hours used to blow the pilot light on the fridge out so i rigged up so the Fridge for 12v when in motion (it was a 3 way fridge) , as 500k or more during the day out bush is quite normal out here .

[jitter]

I ran a thick lead via a 100a relay from the alternator through a plug to the battery in the van for the Fridge , a switch and voltage meter on the Dash , in gas mode sitting on 120k or more for hours used to blow the pilot light on the fridge out

What looks like a pilot light in an absorption type cooler actually is the (whole) burner. It's all that's needed to get the circulation in the cooling system going.

so i rigged up so the Fridge for 12v when in motion (it was a 3 way fridge) , as 500k or more during the day out bush is quite normal out here .

What do you mean with "120k" and "500k"?

[GEuser]

What do you mean with "120k" and "500k"?

Look at the speedo and then look at the tripmeter .

[Delta]

What do you mean with "120k" and "500k"?

Look at the speedo and then look at the tripmeter .

So your first use of "k" mean km/h, and your second use of the exact same thing means km?  Of course!

[GEuser]

What do you mean with "120k" and "500k"?

Look at the speedo and then look at the tripmeter .

So your first use of "k" mean km/h, and your second use of the exact same thing means km?  Of course!

What are you getting picky about?

Its all in the reading , can't you be careful how you read , as if i was sitting on 120k does that mean i'm sitting there on a 120k strip of bitumen , and 500k during the day means 500k hours in 1 day , come on now bored at home with nothing better too do 100000000000000000000009k .

[Delta]

Because this is an engineering forum, and correct use of units is important.

[jitter]

Agreed.

I kinda understood the meaning of 120k because the blowing out of the flame of the cooler hinted at motion. And then 500k per day hinted at distance travelled.
But the usage of just a multiplier (k = kilo = 10³) is confusing because over here, in daily speech, the word "kilo" used on its own exclusively means kilogram (kg). A speed of 120 km/h is either "120" or "120 kilometres per hour". Distance is "kilometres" only (well actually, "kilometre" as we tend to keep (monetary) units single).
And then the accountants like to say "500k" when they mean 500,000... So in non engineering circles it would have been all the more confusing.

On a more general note, often small and capital letters in the SI are used incorrectly. I often see (e.g.) 200 v when it should be 200 V. In that case it doesn't really lead to confusion, but wait until you mix up m (milli = 10^-3) and M (mega = 10⁶)...

And as an aside, all standard SI units are without multiplier with the exception of the kg.

[Another Dave]

Yeah a deep cycle battery, probably a car battery really with a label saying leisure. I have my
doubts as to whether the internals are any different.

2005 ish i paid about £40 for a 110Ah battery, prices increased quite a bit over the next few years
until the same budget battery was approx £110.  Prices have dropped again over the last year
or two. You can pickup a budget 110Ah battery for around £60.

What can this charger teach me, and nope i dont want to plug it in and lick my fingers and
have a poke around it 

What tests can i do and what silly mistakes can i make where the results do not match the theory?

Thanks.

[GEuser]

Us mechanics/lorry bods can talk in our own language aye! Another Dave .

Those prices mentioned are going back a bit , when lead went up worldwide a few years ago battery's went up the next day practically and "Shot" up .

Also that's the trouble with buy on budget items sometimes at least when i have too i look for specifications or stickers on items and then also go by practicability , like for instance the weight of a battery .

I just looked about for a real 200A DCB and are they "Up" there still , a real arm and a leg job btw .

Personally i'd go with whats working atm , and find something else to learn from as the variables are too great (like the type/real size/ fake or not battery , i't be far more of a concern if the battery was a £200 or more real one , one could spend some time and money fitting up low consumption lights? or a vibrating bed? or chook band radio's? see you ha ha ha ...

Happy Vanning .

[Another Dave]

Low consumption lights already done,  vibrating bed is self powered from my snoring or worse

Radio is mains powered.  I never did get around to installing a 12v unit.

Thats why i had a feeling the charger was at fault initially, battery good and no excessive loads
so it left nothing else really.

My last trip confirmed that a ikkle 3.6A charger had no issues with keeping the battery topped up
and it was switched off at night and during the day. Only on whilst the lights were on at night
4- 5 hours or so. and a short burst in the morning after using the waterpump for washing etc.

What to replace it with though?  "proper" caravan chargers are silly money.

Thanks

[Delta]

12v smart chargers can be had cheaply - I got mine for £13 from Aldi (or was it Lidl...?).  Essentially the same as this one.

Benefits; they will charge at their max rate (probably only about 5A on mine) until the battery is full, then switch to a nice gentle float charge, so you can leave it connected.

Not sure how they will react to the loads being connected as it tries to charge, but it sounds like you could just charge overnight.

[Another Dave]

Thats what worried me with the CTEK charger it only gave out 3.6Amps max.

With the lights on at night the charger got quite warm. Fighting a losing battle but only just
i think.  It didnt take long after switching the lights off for the charger to show the green
battery full light.

I thought the ALDI/LIDL one was 3.6Amp also?   The voltage also goes a little high and over time
i think it may cause the battery to gas.

Budget option for a charger and to keep the voltage down to 13.8 max?

Thanks

[Delta]

What about a generic 15V SMPS, with a solar charge controller to look after the battery and power the loads?

Solar dudes - would this work?  Would the controller just stop drawing current from the PSU when the battery is full?

[Another Dave]

I was just about to type i have charge controllers for the solar, but do not use the solar and mains
charger at the same time. Solar packed when we are off grid.

But i re-read your post and i think you mean use that as a charge controller?  Instead of the solar
panel connected, connect a 13v supply to that side and then onto the battery as normal?

Even though it states 20A i have read reviews where they are identical to the 10A ones with no additional
features to handle 20A. Most reviews state they are dountful whether it will handle 10A.

I think i have that one, but its only used with a 25w panel.

[Delta]

But i re-read your post and i think you mean use that as a charge controller?  Instead of the solar
panel connected, connect a 13v supply to that side and then onto the battery as normal?

Yeah, that's what I was getting it, should have been clearer!

You may need more that 13v to give it enough headroom to float the battery at 13.8v.

Maybe start a new thread in the renewables section to see if any of the solar experts can advise.... 

[Another Dave]

They say 13.8v floating, but does it really need to be that high?  I think 12.8v - 13v would suffice in
my situation.   The battery doesnt really get run down and a 6amp charger should keep it
close to fully charged anyway.

As long as it can keep the 13v under load.

Or am i missing something?

[tautech]

They say 13.8v floating, but does it really need to be that high?  I think 12.8v - 13v would suffice in
my situation.   The battery doesnt really get run down and a 6amp charger should keep it
close to fully charged anyway.

As long as it can keep the 13v under load.

Or am i missing something?

You are.

https://en.wikipedia.org/wiki/Lead%E2%80%93acid_battery
<snipped>
Open-circuit (quiescent) at full charge: 2.10 V
Open-circuit at full discharge: 1.95 V
Loaded at full discharge: 1.75 V
Continuous-preservation (float) charging: 2.23 V for gelled electrolyte; 2.25 V for absorbed glass mat (AGM) and 2.32 V for flooded cells. Float voltage recommendations vary among manufacturers due to different lead acid concentration and positive plate grid alloy. Precise float voltage (±0.05 V) is critical to longevity; insufficient voltage (causes sulfation) is almost as detrimental as excessive voltage (causes positive plate corrosion, expansion and electrolyte loss.)
Typical (daily) charging: 2.37–2.4 V (depending on temperature and manufacturer's recommendation)


2.32 x 6 = 13.92V....close to the middle of the old and generally accepted 13.8 -14.2V


http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery


You've asked about chargers.....I say again, stick with your CTEK or get a larger CTEK, they're good stuff.

[Another Dave]

My CTEK got really warm though.  Although it is only rated at 3.6A. This was not far off keeping the battery
close to fully charged.

Would a larger one run cooler or would you recommend additional heatsinking?   The unit is fitted
directly beneath a bed so fans cannot be used unless 100% silent.

No issues with openeing one up and adding additional heat spreaders if that will help it last longer
and no risks of overheating.

[tautech]

My CTEK got really warm though.  Although it is only rated at 3.6A. This was not far off keeping the battery
close to fully charged.

Would a larger one run cooler or would you recommend additional heatsinking?   The unit is fitted
directly beneath a bed so fans cannot be used unless 100% silent.

No issues with opening one up and adding additional heat spreaders if that will help it last longer
and no risks of overheating.

If it's connected all the time it's not likely to run hot unless there's been a period of high draw off as the charger will supply some of the load too but then still needs to top the battery off.
Once the battery is close to fully charged and the draw on the charger low it should run quite cool....leave it connected for some time then check the draw which if more than a few hundy mA indicates the battery is tired.
Not saying it is  but the more you play with these things the more feel you have for what's normal.

Trust the CTEK will not hurt your battery, just monitor it's behaviour for your own piece of mind. 

[jitter]

My CTEK got really warm though.  Although it is only rated at 3.6A. This was not far off keeping the battery
close to fully charged.

Really warm or downright hot? Warm is OK, blazingly hot isn't.

Would a larger one run cooler or would you recommend additional heatsinking?   The unit is fitted
directly beneath a bed so fans cannot be used unless 100% silent.

It looks like you keep the CTEK charger connected and switched on when you're using lights, etc. I don't think that you're supposed to use it that way because of its processor controlled nature.

I looked at the manual, and though it doesn't specifically state that it cannot be used to charge and supply power to a load at the same time, it does state that it should only be used what it's intended for, and that's as a charger. To me this implies that charging AND using stuff like lights must never be done simultaneously, not with this particular charger.

It doesn't look like it destroys the charger, but it will most likely be the reason why it's running hot despite having a fully charged battery. But that's to be expected. With two power sources in parallel, the one with the highest voltage (and that will always be the charger) will supply all the current up to the point that it's capable. Only then will the remaining current come from the battery. So while drawing 10 A, the charger will supply its full 3.6 A all the time with the battery supplying the rest. That's why the charger runs hot.

This is a processor controlled charger that goes through different charging phases to end up with a nicely charged battery. Once you start switching loads in and out, you will upset this programme. This might lead to the charger breaking off a phase and going back to the start, or jump right to the end when the load is switched off. So, the behaviour of the LED going green after switching off the load is not surprising at all IMHO.

Now, the original charger/power supply you started this topic with will basically not behave differently, but it is a non regulated device and it would have been designed with powering the caravan and charging the battery at the same time in mind. With this too, the current drawn will divide between PSU and battery depending on the voltages, but now there's no charging programme to be interrupted. In this setup, everything is determined by the currents drawn by the battery and the load.

No issues with openeing one up and adding additional heat spreaders if that will help it last longer
and no risks of overheating.

This won't be necessary when used as intended. Besides, that CTEK charger will most likely have protection against mishaps, among which should be overheating.

[Another Dave]

Subjective warm/hot.  I could pick it up without getting burnt, but it was hotter than i would have liked
and think it will likely reduce its lifespan quite considerably.

I did contact CTEK and they said it should be OK but would offer no guarantee that it will
work as required. But they did say it should protect itself. Too hot for my liking though.

I think the CTEK is the wrong charger for my application, ideally i want it on 24/7 with no noise and
no heat. Although the caravan chargers are silly money and it seems some have their
own reliability issues and possibly wont last as long as the original one.

After checking some reviews, I wouldnt opt for a used unit because it maybe half dead already.


Thanks

[tautech]

Subjective warm/hot.  I could pick it up without getting burnt, but it was hotter than i would have liked
and think it will likely reduce its lifespan quite considerably.

I did contact CTEK and they said it should be OK but would offer no guarantee that it will
work as required. But they did say it should protect itself. Too hot for my liking though.

I think the CTEK is the wrong charger for my application,

The 3.6A unit, quite possibly.
A bigger unit should run much cooler.

[Another Dave]

I think the problem is im pulling approx the same amperage as the charger can put out and its fighting to keep
it fully charged. I wonder is a smaller fixed amperage charger would work better? 

Need something to just put out a steady charge and stay cool.

[jitter]

Yeah a deep cycle battery, probably a car battery really with a label saying leisure. I have my
doubts as to whether the internals are any different.

Actually, they are quite different.
The car battery, designated SLI for Starting, Lighting and Ignition, is a relatively light construction in which the electrodes are thin and with a large surface area.
This large area facilitates the high current that cranking a cold engine needs. According to this tutorial they are designed to be drained as little as 5% before needing recharging to keep the internals in good condition. Deep cycling will destroy them quickly. Deep cycle/leisure batteries are of heavier construction and can take discharging down to 20% capacity repeatedly.

I think the problem is im pulling approx the same amperage as the charger can put out and its fighting to keep
it fully charged. I wonder is a smaller fixed amperage charger would work better? 

Need something to just put out a steady charge and stay cool.

By the looks of things, your CTEK charger seems to be one of the more popular and proven chargers for use in caravans. I can't help but think that it's quite up to the job, despite my former doubts. As I wrote before, if you're running anything off the battery+charger, the charger will supply everything up to 3.6 A. Anything over will come from the battery.
This means that at more than 3.6 A, you will not be charging but draining the battery, albeit at a lower rate than without charger. As soon as the load drops below 3.6 A will some of the output charge the battery. If the load is disconnected completely, the battery has the full 3.6 A charge available, which it will only take when its charge level is low enough.

IMHO, you can get away with using the CTEK as is. Even if its lifespan is limited by the heat a little, that may still mean you can expect many years of service from it in camping type of use (i.e. a couple of weeks a year).