charging batteries...

[VinceB]

Hey guys,

My setup here is two 60 A*h  and two 130 A*h batteries.

The heavy ones are always hooked up. I use the small ones to go fishing with a 40 lbs electric motor on a small boat.

On a typical day, when I get back from fishing the used battery is pretty much dead at 12 V.  I usually connect it directly to the battery bank which is anywhere between 12.8 and 14 V (depending on the charge coming in from solar and wind).

I am assuming this produces a high current rush into the small battery and it is definitely not the best way to recharge it. But what else could I do?? Any ideas? If it includes changing the basic setup I am also open.

Thank you!

Vincent

[electronbaby]

What time frame do you need the small batteries recharged in? The best way to go would be to pick up a small (10w - 20w) PV panel and a cheap PWM controller and have a separate charging system. OR you could charge off your permanent bank if you were  running an inverter (less efficient, but cheaper by far).

Or you could keep doing it the way you are doing it, and replace your bigger batteries sooner.

[electronbaby]

I suppose you could also use a PWM controller from the bigger bank (that always is charged) to charge the smaller bank. You would have to scout around and check the voltage specs to make sure they would work in your case. Make sure its programmable so you can change the voltage thresholds. You will need to lower them slightly for it to be feasible. Some controllers only charge when the input voltage is in the PV range (16 - 22 vdc for a 12v nominal controller), this would be unacceptable because you should not float your bank that high.

I would personally prefer a separate system if I were you.

[scottsAI]

As is unless your getting sparks like your spot welding then I would not worry about it.

With that said: Correct not good to parallel a charged with a discharged. Don't expect damage to the larger battery, the smaller could be damaged, hopefully over time.

Solution: Charge with a second controller, once near the same voltage then parallel them if you desire.

If the cost is too much, then parallel them with a a high wattage Lamp as part of the connection. The lamp will limit current or using 0.1 ohm resistor, long wire will do it also. Goal is to limit the current when they are put together.

Have fun,

Scott.

[VinceB]

I would say I have about 36 hours to recharge the small battery. I alternate days and use only one at a time.

Using the inverter seems like a practical solution, because I already have a 1000W Xantrex. Cool!

[VinceB]

Ok. The sparks are really small actually. But as rule of thumb, the charging current should be desired to be approx. 10% of the nominal amp-hours of the battery, right? I am thinking when I parallel them directly, the current is much higher, at least for the first minutes (or seconds) ? It's not like it's really charging, but more like it's equalizing voltages...

[scottsAI]

IF the sparks are less than when you jumper a car, then I would not worry about it.

The huge current is in the first seconds of connection.

If worried; use a long thin wire to connect, wait a hour and connect.

Have fun,

Scott.

[Bobbyb]

Assuming your solar/wind can charge the small battery in 36h, can't u just use one diode between the positive of the small to the big battery?

Solat/wind--small bat --diode(-->|-)--big batt.

[VinceB]

Hi!  Could you please briefly describe the purpose of such a configuration? I don't really understand how that would help in charging. The diode would prevent the current from going to the big battery bank to the small discharged one...But in order to recharge the big ones, the voltage of the small would have to be like 1.5 V higher than the big, which seems unlikely to happen...

[Bobbyb]

Hi,

I drew a little picture to make it clearer.





The one with one diode is what I was talking about. With this configuration the small battery will charge first on your system. And when the voltage in the small batt reaches the big batt voltage +0.6V the big will start charging.

Of course the voltage over the small batt will be to high. That's why u need a second diode like in the second picture, now both battery voltages will be the same.

Yes you'll need 0.6V more out of your solar/wind so hopefully that will not be a problem?

If it dose u can try a geranium diode with only 0.3V drop (or use the diodes in a geranium transistor).