Author Topic: Do I need a diode using a bench power supply for charging battery ?  (Read 5849 times)

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Offline haryTopic starter

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Hi

Here is my quetsion :
Do I need a diode using a bench power supply for charging battery ? Is it risky to charge battery with bench power supply without adding a diode in the circuit to avoid current flowing back from battery to the supply in some situation ?
« Last Edit: July 02, 2020, 12:56:56 pm by hary »
 

Offline Ian.M

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Re: Do I need a diode using a bench power supply for charging battery ?
« Reply #1 on: July 02, 2020, 01:33:58 pm »
Maybe!

Unless you are 100% certain your bench PSU is by design protected against damage from applying a voltage source to its output when its switched off or otherwise has its input power disconnected, and wont draw too much current from the battery if switched off or otherwise powered down, you need a diode.  However adding a non-ideal diode brings its own set of problems if you need to get close to 100% charge into the battery.
 
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Offline ArthurDent

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Re: Do I need a diode using a bench power supply for charging battery ?
« Reply #2 on: July 02, 2020, 04:39:44 pm »
At one job I had at a weather station on top of a mountain they had a data logger that was powered by a 12 volt car battery that was always on charge from a Astron power supply. After they had 2 of the power supplies burn up in a short period of time I was asked to find out why. The data logger was quite a distance from the battery and power supply and thunder storms were common on the summit and mains power could be somewhat iffy so they needed the battery for backup.

What was happening was that transients were induced in the long wires connecting the battery to the data logger and the power supply connected to the battery had a protective circuit (an SCR 'crowbar') to protect any device connected to the supply from overvoltage. These spikes caused the SCR to fire shorting the supply output but with the battery connected directly to the output, something had to give, and that was the runs on the circuit board which were vaporized. The solution was to put a diode in series with the new supply output to prevent any voltage being fed back into the supply. Now you could use a mosfet connected as an extremely low forward drop diode and not have to worry so much about full charge.

The Riden RD6006 has a battery charge function which can be helpful
 
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Offline haryTopic starter

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Re: Do I need a diode using a bench power supply for charging battery ?
« Reply #3 on: July 02, 2020, 05:18:26 pm »
Thanks for the response.

But How can I know about a specific power supply model.

For my personal use, I use some little Riden DP5005 or so, and they have this very useful feature for me as I often have to deal with battery.

But at my work, I don't think they would order from AliExpress.

And they'll like something that look more "professionnal".

I was maybe thinking something like this
https://www.welectron.com/Siglent-SPD1305X-Benchtop-Power-Supply
or this
https://www.reichelt.com/fr/fr/laboratory-power-supply-0-60-v-0-6-a-2x-usb-peaktech-6227-p270048.html?PROVID=2788&gclid=CjwKCAjwi_b3BRAGEiwAemPNU3jmylTXhFwN-azHtSvFDLBJhhei0Lr3m4e5iULOHdrZjmwRreJ-oRoCS0UQAvD_BwE&&r=1

I absolutely need the battery charging protection feature.
Otherwise, I'm pretty sure, it won't last, it will be burn after a month or so by one of my colleague or even me by mistake.

But that feature is't cleary advertised !
 

Offline wizard69

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Re: Do I need a diode using a bench power supply for charging battery ?
« Reply #4 on: July 02, 2020, 06:37:48 pm »
Well to n extent it depends upon the supply.    However since most power supplies are not designed to be battery chargers there is a (very) high risk of blowing out the supply!   This actually happened in the tech classes I took many moons ago, somebody wanted to charge a battery and turned off the power supply before disconnection.   zap.   So yeah it does happen and can lead to significant damage.

Hi

Here is my quetsion :
Do I need a diode using a bench power supply for charging battery ? Is it risky to charge battery with bench power supply without adding a diode in the circuit to avoid current flowing back from battery to the supply in some situation ?
 
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Offline haryTopic starter

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Re: Do I need a diode using a bench power supply for charging battery ?
« Reply #5 on: July 02, 2020, 06:57:25 pm »
So I'll insist with my company to get a Riden RD6006, even if it's sold as a kit !
 

Offline David Hess

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Re: Do I need a diode using a bench power supply for charging battery ?
« Reply #6 on: July 03, 2020, 08:35:27 pm »
But How can I know about a specific power supply model.

Check the schematic included in the documentation.  You selected your power supply because it came will full documentation including a schematic, right?  RIGHT?
 

Offline wizard69

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Re: Do I need a diode using a bench power supply for charging battery ?
« Reply #7 on: July 03, 2020, 08:45:07 pm »
Not at all.   If this is for a commercial operation force them to buy a batter charger designed for the job at hand.   I can imagine any company being in a position where they can't buy a proper battery charger.   Beyond that there are liability issues to consider.   This isn't a situation where a hobbyist is working at his bench.

So I'll insist with my company to get a Riden RD6006, even if it's sold as a kit !
 

Offline janoc

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Re: Do I need a diode using a bench power supply for charging battery ?
« Reply #8 on: July 03, 2020, 09:18:20 pm »
So I'll insist with my company to get a Riden RD6006, even if it's sold as a kit !

Why not get an actual, proper charger for your battery? Which actually includes also various safety features against overcharging the battery, charging a damaged battery, overheating and starting a fire?

Buying a bench power supply to charge batteries is a very dumb (and potentially really expensive!) idea.
 

Offline ledtester

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Re: Do I need a diode using a bench power supply for charging battery ?
« Reply #9 on: July 04, 2020, 12:35:04 am »
... However adding a non-ideal diode brings its own set of problems if you need to get close to 100% charge into the battery.

Would a power supply with remote sensing solve this problem - i.e. when using it as a charger, add the  diode (say at the positive terminal) and sense at the cathode of the diode?
 

Offline ArthurDent

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Re: Do I need a diode using a bench power supply for charging battery ?
« Reply #10 on: July 04, 2020, 02:48:30 am »
... However adding a non-ideal diode brings its own set of problems if you need to get close to 100% charge into the battery.

Would a power supply with remote sensing solve this problem - i.e. when using it as a charger, add the  diode (say at the positive terminal) and sense at the cathode of the diode?

Generally there is a limit to the voltage difference between the output terminal and the sense terminal for that output terminal, generally less than 1 volt. Exceeding that value could damage the sense circuitry in the supply and this limit could be exceeded if the battery was feeding voltage into the supply through the sense leads while the output terminals were isolated by a diode. It would be safer to compensate for the fraction of a volt diode drop from a mosfet connected as a near ideal diode.

https://www.edn.com/power-supply-remote-sense-mistakes-remedies/
« Last Edit: July 04, 2020, 02:50:11 am by ArthurDent »
 
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Online JustMeHere

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Re: Do I need a diode using a bench power supply for charging battery ?
« Reply #11 on: July 04, 2020, 03:11:33 am »
It's not a bad idea.  If you see a spark when you hook it up, you probably should.

I've done this with a TP3005.  I had a spark w/o the diode. 
 

Offline Gregg

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Re: Do I need a diode using a bench power supply for charging battery ?
« Reply #12 on: July 04, 2020, 04:02:02 pm »
From a comparison chart copied from Banggood's website it appears that the Riden DPS5005 is rated to charge batteries.
I have a Riden DPS3012 set up to float 4 large flooded lead acid spare cells on a friend's off grid setup; this little power supply has been in use for three years constantly without issue.  The input is 24V nominal and the output is 9.06V; I have 10A automotive style fuses on both the input and output.
 

Offline haryTopic starter

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Re: Do I need a diode using a bench power supply for charging battery ?
« Reply #13 on: July 04, 2020, 05:24:32 pm »
Actually, the main purpose for that power supply isn't for charging battery.

It's meant to test an embedded system that works on battery.

When it's plugged to the main, the charger will charge the battery. When unplugged, the system will run on its own battery.

But as I need to test the charging "algorithm" and the battery management depending on voltage level (lead acid battery), I need some kind of way of  simulating the battery voltage changing and see if the system switch off as expected when the voltage is too low, or allow the system to start if the battery is ok.

So if I power the system from the bench power supply, when plugged in the main, in case of simulating a dead battery, the main supply will inject power back to the bench power supply.

That's the reason I wanted a bench power supply  that can charge battery without any problem.

 

Offline Trader

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Re: Do I need a diode using a bench power supply for charging battery ?
« Reply #14 on: February 04, 2023, 03:45:35 am »
I'm using a PSU to charge a 6V VRLA battery and, since I don't know if my PSU has backfeeding protection, I'm using a 1N5822 (Schottky diode with low drop-voltage).

But I found that using an Ideal Diode (2 MOSFETs with a control circuit around them) could be better.

Any opinions?
 
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Offline shapirus

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Re: Do I need a diode using a bench power supply for charging battery ?
« Reply #15 on: February 04, 2023, 12:06:56 pm »
as a side note, FWIW, I have yet to see a PSU (at least of the CC/CV capable ones) that would be damaged by backfeeding from the battery. I have, however, seen ones drawing significant current, for example, 50 mA. The lowest I have seen was 2 mA, and a typical DC/DC buck module from Aliexpress will draw about 14..20 mA.

(all current values were measured with ~12-13V batteries)

I'm using a PSU to charge a 6V VRLA battery and, since I don't know if my PSU has backfeeding protection, I'm using a 1N5822 (Schottky diode with low drop-voltage).
This works and gets rid of the guesswork concerning the possible PSU damage or the parasitic battery drain, but, however low the diode voltage drop is, it is still non-zero. It wouldn't be much of a problem if it was only non-zero (just crank up the CV setting, and you're fine, right?), but it's also not constant and depends on current, thus making it impossible to set a precise final voltage, unless the PSU has a dedicated set of wires to sense it right at the battery terminals.

But I found that using an Ideal Diode (2 MOSFETs with a control circuit around them) could be better.
It will definitely be better. Please share the circuit you have in mind (or maybe even tested?). I would be interested to try one myself.
« Last Edit: February 04, 2023, 12:40:29 pm by shapirus »
 
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Offline blackdog

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Re: Do I need a diode using a bench power supply for charging battery ?
« Reply #16 on: February 04, 2023, 02:01:39 pm »
Hi,

Yes always include and diode in series for your safetyy!
Modern batteries get more and more energy and many quickly forget this and how dangerous it can be.
People are walking away from the installation that charges the batteries etc.

Of course I am aware, that some power supplies can stand it if you reverse the + and -, but there are not many of them, especially in the hobby circuit.
Even if you would not reverse the polarity of the battery to be charged, it can still go well wrong.

If the power supply is turned off power transistor can get a reverse voltage, not every power supply has a diode built in for this.
Another example, the battery is 24V and the power supply is set to 5V, BANG! if you don't use a diode.
And I know of other situations that can cause battery charging to go wrong....

Charge batteries with chargers made for that!

Still use a Power Supply, then include a suitable diode!
Charge Li-Ion? use a suitable charger!

I know many who disregard this advice, on a Dutch forum the same discussion, and then find it strange that their Power Supply burns out....
Comments like this then come along, if I include a diode I can no longer charge exactly to 4.25V,
that's what I mean, take a suitable charger and not your Power Supply.

But, do what you yourself find suitable, I choose safety, this to keep my measuring equipment in one piece and then my LAB does not burn down.

And now let's wait for the first one to come forward with the comment that he has been doing it for years without a diode
and has never had any problems, good for you!  :-DD

Kind regards,
Bram
Necessity is not an established fact, but an interpretation.
 
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Offline shapirus

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Re: Do I need a diode using a bench power supply for charging battery ?
« Reply #17 on: February 04, 2023, 02:16:02 pm »
Using equipment not exactly designed for the job is not inherently unsafe. It only puts additional responsibilities on the user to keep the process safe, most important of which is a full understanding of exactly what processes take place and what constraints have to be met to stay in the safe operating area. When charging a lithium battery, for example, there are not many of them, pretty much limited at:

- do not exceed max allowed voltage per cell (and min voltage for discharge);
- do not exceed max allowed current, both charge and discharge;
- make sure that the temperature stays within the allowed range and that the battery charged at a low ambient temperature is not then stored at a much higher temperature being still fully charged.

As long as these conditions are met, the battery does not care if it is being charged with a designated charger. It's up to the user to make sure that they are met, either by utilizing his (her?) own knowledge and experience, or by relying on those of the charger manufacturer's.
« Last Edit: February 04, 2023, 02:17:48 pm by shapirus »
 

Offline blackdog

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Re: Do I need a diode using a bench power supply for charging battery ?
« Reply #18 on: February 04, 2023, 03:14:33 pm »
Hi shapirus,

The issue is not whether the battery is aware of how it is being charged.
The issue is that the person connecting a battery to a Power Supply is aware of what dangers it can pose if he or she does not think about what they are doing.

Much of humanity is pretty lazy, I'll do it this way, oh well for that one time it can be done the quick way, etc.

And YES!
- do not exceed max allowed voltage per cell (and min voltage for discharge);
- do not exceed max allowed current, both charge and discharge;
- make sure that the temperature stays within the allowed range and that the battery charged at a low ambient temperature is not then stored at a much higher temperature being still fully charged.


Just look at the many youtube videos that will make your neck hairs stand up.
Most people often become aware of the consequences when confronted with them.

This question is in the beginners section and I think it is good to point out to beginners, what the safe practice is for charging batteries.

Kind regards,
Bram
Necessity is not an established fact, but an interpretation.
 
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Offline Siwastaja

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Re: Do I need a diode using a bench power supply for charging battery ?
« Reply #19 on: February 04, 2023, 03:20:25 pm »
In my opinion, definitely no diode needed.

But there are some total and utter crap "bench power supplies" that die on a battery load, or pre-biased capacitive load. But even if you use the diode, these con devices will die from any other random cause anyway, so the sooner they self-destruct, the better, so you can claim for money back and learn the lesson what to buy.

Yes always include and diode in series for your safetyy!
Modern batteries get more and more energy and many quickly forget this and how dangerous it can be.

Dangerous "advice." DIODE IS NOT A SAFETY DEVICE. A diode easily fails as a short circuit. If in doubt about the quality of bench supply, use a fuse (in addition to / instead of a diode), which is an actual safety device. With a battery that can source a lot of current, a fuse with high interrupt rating is recommended; a sand-filled type for example (always read the datasheet).

Of course, one can not leave a bench power supply charge a li-ion cell without monitoring.

Charging batteries with lab supplies is their normal intended use, but you need to know exactly what you are doing, and monitor the battery pack, acting as a battery management system yourself.
« Last Edit: February 04, 2023, 03:22:26 pm by Siwastaja »
 
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Offline shapirus

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Re: Do I need a diode using a bench power supply for charging battery ?
« Reply #20 on: February 04, 2023, 03:22:02 pm »
The issue is that the person connecting a battery to a Power Supply is aware of what dangers it can pose if he or she does not think about what they are doing.
Yes, this is precisely what I meant referring to the knowledge of the processes that are taking place. Another issue here is that the user must not only think that he/she has the knowledge, but actually have this knowledge.

OTOH, it's not rocket science. Know what to avoid, know what to do, know what to measure and how to measure properly, know the Ohm's law, ideally have a fire-proof metal case handy (if you're playing with Li-ion/LiPo stuff), make sure you know what you're doing and you'll be good to go. How do you get experience if you don't do anything?
 

Offline blackdog

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Re: Do I need a diode using a bench power supply for charging battery ?
« Reply #21 on: February 04, 2023, 03:52:39 pm »
Siwastaja

You are the first!  :-DD

In my opinion, definitely no diode needed, That's nice advice, did you really think before typing it here?

Dangerous "advice." DIODE IS NOT A SAFETY DEVICE.,
Another comment that hasn't really been thought about I think,
A 1N4148 is not a part you are going to use e.g. for a charging current of say 4-Ampere, for that you use a diode that can handle well over the charging current needed and also the difference voltage between the battery and the power Supply.
Include an extra fuse for safety, my blessing you have, basically a good idea.


Who told you this: Charging batteries with lab supplies is their normal intended use
Just a small peace from een KeySight power supply, with only one possibility of what could go wrong ...

Reverse Current Loading
Active loads connected to the power supply may actually
deliver a reverse current to the power supply during a portion
of its operating cycle. An external source can not be allowed
to pump current into the supply without loss of regulation and
possible damage to the output capacitor. To avoid these
effects, it is necessary to preload the supply with a dummy
load resistor so that the power supply delivers current through
the entire operating cycle of the load devices.


And a little more general info on this topic from KeySight:
https://edadocs.software.keysight.com/kkbopen/what-can-cause-a-power-supply-output-voltage-to-exceed-its-setting-583423316.html

Kind regards,
Bram
Necessity is not an established fact, but an interpretation.
 

Offline Siwastaja

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Re: Do I need a diode using a bench power supply for charging battery ?
« Reply #22 on: February 04, 2023, 04:48:51 pm »
"possible damage to the output capacitor" just means they have a capacitor at output, which is obvious, and if you apply a battery voltage which exceeds the voltage rating of that capacitor, it might get damaged. Quite obviously, the battery voltage must be within the range of the supply.

Also one can claim that the inrush current of suddenly connecting a battery could damage the output capacitor, but the current is exactly the same when just shorting the output of the supply.

The difference is here:
Bullcrap power supplies blow up when you connect a battery, and the manual probably says nothing about it (if there is a manual at all).
Keysight supply will definitely not blow up, but they nevertheless cover their bases in their manual. Instead of having to specify stuff like "external battery voltage must be between xx - yy V", they just say don't do it.

And loss of regulation? No shit Sherlock, that's obviously what happens, unless it's a two-quadrant supply. Loss of regulation does not mean damage.

Some lab supplies have a configurable OVP with possibly some hard limit beyond the maximum output voltage. Know your equipment.
« Last Edit: February 04, 2023, 04:54:43 pm by Siwastaja »
 

Offline Siwastaja

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Re: Do I need a diode using a bench power supply for charging battery ?
« Reply #23 on: February 04, 2023, 04:56:24 pm »
Who told you this: Charging batteries with lab supplies is their normal intended use

I told you. Some of us do this professionally instead of passive aggressive shitposting. Uses of lab supplies are various. They are pretty useless if you have to construct special circuits for every basic need. Prebiased loads are completely normal and not limited to batteries. Just any normal DUT can have tens of thousands of uF of input capacitance.
 

Offline Siwastaja

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Re: Do I need a diode using a bench power supply for charging battery ?
« Reply #24 on: February 04, 2023, 04:58:22 pm »
And a little more general info on this topic from KeySight:
https://edadocs.software.keysight.com/kkbopen/what-can-cause-a-power-supply-output-voltage-to-exceed-its-setting-583423316.html

It would be nice if you read your own links...

It is possible for an external source of power (such as a battery, charged capacitor, inductor with changing current, or another power supply) to cause the voltage to go above the setting. The OVP will respond to this condition as outlined above. If the external power source can provide more current than the rating of the power supply and an SCR circuit is used in the power supply, it is prudent to put a fuse in series with the external source of power to prevent damage to the power supply SCR and/or output circuit from excessive current.

TLDR: nothing about diode. Use a FUSE.

Another question for you, what do you think the current will be when the output capacitor with ESR=X and voltage=Y is connected to a battery with ESR=Z and voltage=Å? Hint: the fact that you set the current limit at 4A is meaningless. Question: what do you think happens to your 4A rated diode? Do you know how to interpret SOA curves?
« Last Edit: February 04, 2023, 05:00:49 pm by Siwastaja »
 


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