Author Topic: 12V lead acid battery question...  (Read 901 times)

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Offline PwrElectronicsTopic starter

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12V lead acid battery question...
« on: May 13, 2024, 06:33:53 pm »
Spring weather finally arrives in my area.  :) So, break out the mower.  :-\ Turn key, and its dead of course...  >:(

I got my old time charger (the sort with a transformer, rectifier, circuit breaker, and ammeter w/o anything else or smarts, etc).

Connect it up.  No current is initially drawn.  Then, slowly the current rises, and rises, and rises!  Eventually pegs the ammeter and then the circuit breaker trips.  It has an auto-reset breaker so it came back on and did the same thing.  Let it go a few times before I disconnected it.

I then checked the battery voltage with my DMM and it was something like 2-3V.

I went and got a current limited DC bench supply from my home lab and set that for about 1-2A.  It did not take too long before the supply switched from CC to CV (supply set at 13V).  Took off the supply and checked the battery voltage.  Now at something like 10-11V.  So, I put the bench supply back on and left it for about 30 minutes.  I then removed it and put the battery charger back on.  Charger is now sourcing ~5A with applied voltage about 15V.  Left that on for another 20min or so.

Removed charger and tried to start the mower.  Success!  I ended up mowing for a while before other problems cropped up (failing belt) but was able to restart it a couple of times OK.

I guess I will find out in a week or 2 but wondering if this battery is EOL ?  Years ago, remember a battery in my winter car (that sat all summer) was dead and took no charging current.  But, for fun I left the charger on it for a few hours and when I checked it later it was taking a charge.  That battery went on to last a couple of years longer.
 

Offline Benta

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Re: 12V lead acid battery question...
« Reply #1 on: May 13, 2024, 08:32:40 pm »
And the question is?
 

Offline Stray Electron

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Re: 12V lead acid battery question...
« Reply #2 on: May 13, 2024, 09:23:41 pm »
     OP  That sounds like a nice problem to have. The OP must be somewhere in the northern US where they don't use their mowers for months on end.  Here we mow at least every other week, even in the winter. By the end of summer, we mow twice per week.

     Get a Battery Tender or some other small regulated 12 voltage power supply and leave it connected to your battery over the winter. Problem solved. 

    You're lucky that your battery recovered and you didn't have to buy another one! 
 
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Offline PwrElectronicsTopic starter

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Re: 12V lead acid battery question...
« Reply #3 on: May 13, 2024, 11:53:12 pm »
Quote
The OP must be somewhere in the northern US where they don't use their mowers for months on end.

Yes, upper midwest/west abt 270km south of the US-Canada border.  Mowing season runs from usually mid May to mid October.

For sure hoping to not need a new battery just yet.  Cost of even small batteries has gone up considerably the past few years.

I was just surprised at the behavior here as I have not seen this before.  The more modern chargers would not even attempt to charge this as they shut down if the target battery is "too dead".
 

Offline David Hess

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Re: 12V lead acid battery question...
« Reply #4 on: May 14, 2024, 12:58:14 am »
When a lead-acid battery is discharged, the lead and lead-oxide is converted to amorphous lead sulfate.  If left for too long without recharging, the amorphous lead sulfate crystalizes and becomes high impedance.  This is what happened to your battery.

A battery in this state may start charging after a while, however it will remain severely damaged and have a short remaining operating life.  Plan on replacing it soon.
 
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Offline floobydust

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Re: 12V lead acid battery question...
« Reply #5 on: May 15, 2024, 04:23:24 am »
Why do all your products float charge at 14.6V?  This is not good, it should go down when current falls below say 500mA so the battery does not boil dry.
Do you use CapXon junk electrolytic capacitors?
 

Offline Refrigerator

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Re: 12V lead acid battery question...
« Reply #6 on: May 16, 2024, 06:16:30 am »
Meanwhile i leave my mower in the open under the rain and snow during winter and when the time comes to mow grass it starts right up with a couple pulls. No pesky batteries needed here.
And it does it on the same old gasoline. Also i've never changed the oil once in that engine over the past however many years that we've had it.
If it ain't broke don't fix it  ;D
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Offline Bicurico

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Re: 12V lead acid battery question...
« Reply #7 on: May 16, 2024, 09:55:17 am »
@Refrigerator:
That is bad advice. OP has an auto-start mower with battery. Unmantained, the battery will deteriorate and die.
But there are other things to consider:

1) Old gasoline will deteriorate and decompose. It will create some sort of nasty thick stuff that will block your carburetor, so you will need to disassemble and clean it.
2) Not changing oil might cause no noticable issue, until it is too late. You will deteriorate the combustion chamber and all movable parts.
3) Leaving the mower in the sun, rain, snow will ensure all plastic and rubber parts deteriorate. All metal parts will suffer unnecessary oxidation.

But it is true:

I have two mowers, one with an MTD motor (old mower), the other with a Briggs&Stratton 500E (new mower).

The old one was replaced due to many broken parts (wheels, handle, etc.). It was stored for more than a year in a humid shed. Never replaced the oil and never gave it any special treatment.

The new one has been maintained by the book. Yet, I had to clean the carburetor (tip: you get a replacement one at AliExpress for a ridiculous price).

When this happend (wouldn't start anymore), I finished the lawn with the old one: put some gasoline in it and pulled the cord: started at the first attempt! Quite impressive, actually.
 
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Offline Refrigerator

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Re: 12V lead acid battery question...
« Reply #8 on: May 16, 2024, 10:37:22 am »
Our mower has been in a fire and the plastic bits are all melted. The fuel tank is full of grit and looks like a swamp.
The thing is over 10 years old and has been stored this way ever since we bought it.
We had to replace some parts, sure. For example the blade broke in half when i pushed it over a stump. Carb was replaced maybe 5 years ago. Pull cord broke and was replaced with whatever string we had laying around.
It just keeps on going, which i find quite impressive. Funny how sometimes my relatives won't be able to start it no matter how hard they try, but then i come and it seems like the mere fact of me touching the mower makes it fire right up.

I added a pic from google of what looks like almost the exact AL-KO model we have. Just in case anyone wanted to know.
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Offline BrokenYugo

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Re: 12V lead acid battery question...
« Reply #9 on: May 16, 2024, 02:02:26 pm »
It doesn't take much to start a mower, such small engines have an automatic compression release for easy hand starting and a fairly low power starter to match. The U1 in my trashy mower is about 6 years old and has needed a good cooking on the dumb charger (DANGER, HYDROGEN, NO SMOKING) the last 3 springs, then it works, but with low capacity. You get about 2 start attempts from it now, maybe 3 on a hot day, but that's good enough unless something goes wrong.

Seems they last a little longer on the engines with a voltage regulator vs the cruder charging systems found on some cheaper engines, said trashy mower floats the battery to like 16 volts.
 

Offline tautech

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Re: 12V lead acid battery question...
« Reply #10 on: May 17, 2024, 10:05:26 am »
I was just surprised at the behavior here as I have not seen this before.  The more modern chargers would not even attempt to charge this as they shut down if the target battery is "too dead".
Normal.
Unless there is some charge remaining the modern smart charger will not initiate a charge.
Typically some 6-10V.

However they can be bluffed by momentarily connecting another sound battery in parallel to the dead one which will kick off the charger and the good battery can then be removed.

But as David Hess correctly points out, unused batteries will sulphate and deteriorate, much shortening their life.

For the ordinary LA battery I have a practice of freshening their charge when not in use every 4 weeks with an overnight charge from a smart charger.
YMMV
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