Float voltage of 2 golf cart battery in series???

[gambit1982]

Hi there, I recently purchased two golf cart batteries at costco. I would like to series them to make 12 volt. I have a BZ MPPT charge controller and about 250 watts of solar panels. My question is, what should I set the float voltage to to charge the series batteries? Any help would be greatly appreciated.

Steven

[altosack]

The BZ MPPT should have a setting for flooded lead acid batteries, which is what you want. If you want to set the actual number, shoot for 14.4V absorb, 13.4V float.

If you don't know the difference between absorb and float, ask, but too often I explain more than necessary so I won't explain unless you ask !

Best Regards,

Dave

[gambit1982]

Hey, thanks for the reply. Sure, I'll take any advice you can give me. So what's the difference between the two? I play around with the float on the mppt charge controller and i set it to 14.6volt, but this was on my walmart 12volt deep cycle marine battery. Is that too high? Because I noticed when you start up a car, the voltage reaches over 14 volts, so I thought that was normal, taht's why I set it to that point. But I just want to stay on the safe side now since I got new golf cart batteries. Thanks again for the info.

Steven

[AbyssUnderground]

Absorb is the period where the battery takes a lower current but slightly higher voltage to fully charge to 100%. A bulk charge will bring it up to around 90%. Absorbsion gets it to 100%.

Float is the voltage you should continue trickle charging at when it is fully charged.

Absorbsion - 14.0-14.4v for (in my case) 3 hours

Float - 13.4-13.8v continuously when charged

[altosack]

I might add that there are 3 stages to good LA battery charging (ignoring equalization):

1. Bulk charging when you take as much current as possible from the charging source; this will get you up to around 70-90% charged depending on the charge rate.
   
2. When the voltage reaches the absorption cut-off, the charge controller starts tapering off the current to maintain the voltage. There are two ways to end this stage; the cheaper controllers time it to be about 2-4 hours, depending, the good ones allow you to put in a cut-off current that when it tapers below that, you're done. Actually, I don't know of any that do this (I think some of them, like the Outback and my TriStar, try to figure out what it should be instead of letting you put it in); when I build my own, I'll put that little feature in.
   
3. Float, as described previously.
   
   

Dave

[altosack]

I just looked up the MPPT250, and it only has 2-stage charging ! And it has no equalize stage !

Both of these are just unacceptable for a charger that costs this much. People, be aware and stay away; there are much better chargers available for that price. MPPT is not worth the money if your batteries don't last as long. Sorry Steven, but maybe others can learn from your misfortune.

Considering that you are charging at about 250W/14V/~220A-hrs = C/13, I would set your float rather high, at about 13.8-14.0V (the charger default is 14.1, which is OK). You will have to check your water level more often, but they will charge more fully this way.

If you want your batteries to last, find a way to equalize them and float them properly. Maybe check Ebay for a C35/C40 ?

Dave