Safe DIY 12v charger for big SLA battery?

[nzo]

Hi all,

I was lucky enough to score an almost brand new 350AH SLA deep-cycle battery that was redundant in a big data center battery bank setup. So heavy I could hardly lift it.

I have a 50 watt solar panel I use to charge and top up the batteries in my ham shack, that power various bits of gear such as a Yaesu FT-1000MP 100 watt SSB rig.

The solar panels are controlled by a 10 amp charge controller. The transceiver runs off the big battery for a couple of hours but after that I can see the led display flickering as it's coping with lower amps.

My question has to do with what kind of 230vAC charger I can throw into the mix to help sustain the transceiver for a bit longer? At present I use a small car battery charger with selectable boost charging or automatic trickle.

I'm a little paranoid about damaging my big 350AH battery through not treating it well by using the wrong equipment to top it up.

Your advice and brilliance is highly appreciated, although I'm not any kind of expert. Throw it at me anyway - show no mercy

[Simon]

you can safely charge ar 10% capacity and I'd guess that if you regulate to the correct charging voltage (13.8-14.4) the current will take care of itself based on the battery spec.

[ConKbot]

I'd find a proper multi-stage charger as "proper" lead acid charging is rather indepth and DIY definitely wont be a cost saving venture. 

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

as you can see there is the general bulk/peak/float charge, but there is also an equalization charge (if its a flooded lead acid, or AGM with a catalyst to recombine gasses)  which should be applied periodically, along with desulphation as feature. 

Since you are using it for something cyclical, youre definitely gonna want a battery charger which does the peak charge,  slapping it on a current limited 13.8V power supply will work for a while, but the battery will eventually become sulphated from never getting a full charge.


something like http://www.batteryspace.com/leadacidsmartcharger10afor12vleadacidbatteryforworldwideuse.aspx would be a start *IF* the voltage match up with the manufacturers battery datasheet.  AGM batteries "float" at a different voltage then FLA batteries, generally lower, but if they manufacturer used something besides pure lead plates, the voltages change again. 

In short:  If you want the life quoted by the manufacturer, you have to follow whats in the datasheet.


Also, dont believe the concrete + battery wives tale you always hear.

[Balaur]

There are some solar panel charge controllers that can be had with not a lot of money. Or there are some bloody expensive ones, if you prefer it that way.

For a DIY approach, you will basically have to limit the solar panel voltage to a specified value. With some luck, there may be some maintenance or cycle voltage printed on the battery or in the datasheet. Most recommendations are for a maintenance voltage of 13.2-13.4V or a bit more (in any case less than the gassing voltage of 14.4V), with a limit of the maximum charge current to let's say C/10-C/5 (which is a lot in your case)

There is some good stuff here or all over the web.

[BravoV]

Another good reference on different treatements at different SLA types by battery charging methods, even though its more forgiving on charging voltage say compared to Li-Ion, to gain longer life, watch the charging voltages at different stage.

Link -> http://www.pacificpowerbatteries.com/aboutbatts/Deep%20Cycle%20Battery%20FAQ/dcfaq6.html

[nzo]

What a goldmine. Thank you guys!

[SeanB]

Also read through the papers at www.battcon.com as it has a lot of info about how to handle and use them.

[NiHaoMike]

Just use a switching power supply, with some way to limit the charge rate to less than C/10 or so. You can set it for 14.4V for a bulk charge or 13.8V for a float charge. You can also set it to 12.8V to maintain the charge.

BTW, the strategy I use for my PC backup battery is to leave the charger set to 12.8V most of the time (to maintain other loads connected to the battery), with a timer (integrated into the power control microcontroller) raise that up to 14.4V for about an hour every week, along with a 10 second test every month. If the battery voltage starts rising above 14.4V due to external causes (alternative energy source), the microcontroller commands the DC/DC converter to start using the excess current. If the battery voltage drops below 12.6V for any reason (power failure or just after a long duration test), it enters a state where it forces the charger on and then waits for the battery voltage to reach 14.4V (and hold for 2 hours) before returning to normal operation. An extended power failure or an internal fault in the system that causes the battery voltage to drop below 11.2V commands the host system to shut down (though it gives a 30 second grace period that the user can cancel if needed). (Note that I used 11.2V instead of 10.5V to leave some power left for critical loads.)

[nzo]

Ni Hao Ma Mike and thank you.

Just use a switching power supply...

Sheesh Mike - you're giving me more than will fit on my plate. I'm an unsophisticated newbie. I understand switch mode PS but you lost me with "microcontroller etc". I imagine this is not part of a store-bought SMPS.