Battery maintenance: Lab power supply == best 6-volt charger?

benthere

TLDR: Looking for a manual 6-volt battery charger?  Consider a bench-top power supply.

We got snow followed by uncharacteristically cold weather while on vacation for Christmas and the new year...

I had to break down and ask some friends from work to clean our solar panels and start the generator but it was too little, too late.  We arrived home to find that our battery bank had a frozen cell.  Once thawed the SG read 1.05 on that cell.  I wrote the battery off as dead and raced to another state to get the closest replacement.

Before I got a chance to install the replacement battery the SG started to come back on the previously-frozen cell.  The rest of bank was in pretty good shape and so began my search for a good 6-volt battery charger.  I found nearly nothing.  Most chargers available are low-amperage and "smart" chargers.  A very helpful tech at Battery systems indicated that I needed a manual charger capable of charging 10% of C20 and suggested a manual "roll around" charger like auto shops used in the days of yore.  That seems like the kind of thing that you should be able to buy at a yard sale for $20 but try to find one on demand!  Associated Equipment still offers manual chargers that can do 6-volts but those things are expensive!  They are also very large and don't charge at the voltage an EQ cycle calls for.

Thankfully, in my search for a 6-volt charger, I ran across a Battery University article about using a lab power supply as a manual battery charger!  I then found and bought a variable power supply rated for 0-15V at 0-40A.  I haven't had that power supply for 24-hours yet and have effectively used it to restore my problematic battery without having to cook the other batteries in the bank!  This worked beautifully; I was able to charge one battery in my string while powering the charger from my inverter running off the same string!

There is one caveat that is not mentioned in the Battery University article;  it seems that some lab power supplies can be damaged if a battery is connected to the output terminals while the power supply is off.  I powered up the power supply and set my voltage before connecting my battery.  It appears that a diode can be installed to address that issue while also reducing voltage slightly making it necessary to set the charge voltage with a voltmeter at the battery.  I intend to make that modification in the future.

I am posting this because the information was hard to find and I am very happy with the results.  I now realize that a good 6-volt charger should have been part of my off-grid setup all along.

jonr

Others should keep in mind "manual".   So unlike most modern chargers, you need to keep an eye on current and dial down the voltage  before it overcharges.

BB.

Sounds like a good solution for saving individual batteries.

-Bill

mike95490

 It appears that a diode can be installed to address that issue while also reducing voltage slightly making it necessary to set the charge voltage with a voltmeter at the battery.  I intend to make that modification in the future.

Be sure you size the diode and heat sink properly.   I'd suggest a Schottky diode and calculating .5V @ 40A  is 20 watts of heat, which may even need a fan on a heat sink

jonr

I'd put a resistor in series and then test if your power supply draws any current from a battery.

If so, I'd use an ideal diode (far less heat):

https://www.analog.com/media/en/news-marketing-collateral/solutions-bulletins-brochures/IDP-web.pdf

benthere

Thanks for the protection circuit suggestions.

I contacted the power supply manufacturer who claims that there is an over-current protection circuit that will prevent damage to the power supply if a battery is connected while powered off or if power fails while connected.