Charging batteries in series

[simplystressed]

Hello - I have two 12V batteries wired in series for my 24V trolling motor. I also use one of the batteries to run all the 12V accessories.

I have two 12V chargers....is it ok to charge the batteries while everything is connected? Or should I disconnect the series link and/or the accessories?

Also wondering if its safe to charge the batteries while on the boat, its open on the top of the compartment so venting isn't an issue, but they're both in wooden enclosure not sure if there's any concern there.

Thanks in advance!

SS

 

[Silvertip]

Re: Charging batteries in series

Using two separate chargers may present a problem and it involves grounding schemes within the chargers themselves. Moder dual bank smart chargers for example, have totally isolated +12 volt and ground pairs so there is no issue with charging series connected batteries. If there is any chance that the ground wire in either charger is electrically tied to the neutral or ground connection in the charger then yes, there is a problem and you will have sparks. Unless you know how to verify what I just mentioned, I would simply disconnect the series jumper and then it would be safe to use both chargers. To simplify this even more, add a heavy duty switch in that lead so you don't need to disconnect anything -- although that still requires that you remember to flip it before connecting the chargers.

 

[simplystressed]

Re: Charging batteries in series

Using two separate chargers may present a problem and it involves grounding schemes within the chargers themselves. Moder dual bank smart chargers for example, have totally isolated +12 volt and ground pairs so there is no issue with charging series connected batteries. If there is any chance that the ground wire in either charger is electrically tied to the neutral or ground connection in the charger then yes, there is a problem and you will have sparks. Unless you know how to verify what I just mentioned, I would simply disconnect the series jumper and then it would be safe to use both chargers. To simplify this even more, add a heavy duty switch in that lead so you don't need to disconnect anything -- although that still requires that you remember to flip it before connecting the chargers.

I've attached a rough diagram of my setup. I don't know what you mean by the ground though If you want I'd appreciate a PM on how to confirm this it doesn't sound like it should be tied to the other charger. I could contact the manufacturer to see if this is the case though?

 

[Silvertip]

Re: Charging batteries in series

I don't want to get into the basics of DC circuitry here but if you look at your setup and connect two separate chargers, you end up with the negative lead from the charger connected to the battery on the right, connected to the POSITIVE terminal of the battery on the left. That happens to occur because the jumper between the two batteries is there. If there is common connection between the two grounds on the two chargers you will get sparks. That connection can be through the power cord. In order to verify if you have a common ground, disconnect both chargers from the batteries and the wall outlet. Connect an ohm meter between the negative leads of both chargers. Now touch the two ground pins on the two power cords together (you won't get a shock). If you get a reading (any reading) you cannot use both chargers at one time unless you disconnect the jumper between the two batteries. If you don't have an ohm meter or know how to use one, then just disconnect the jumper and charge away.

 

[simplystressed]

Re: Charging batteries in series

I don't want to get into the basics of DC circuitry here but if you look at your setup and connect two separate chargers, you end up with the negative lead from the charger connected to the battery on the right, connected to the POSITIVE terminal of the battery on the left. That happens to occur because the jumper between the two batteries is there. If there is common connection between the two grounds on the two chargers you will get sparks. That connection can be through the power cord. In order to verify if you have a common ground, disconnect both chargers from the batteries and the wall outlet. Connect an ohm meter between the negative leads of both chargers. Now touch the two ground pins on the two power cords together (you won't get a shock). If you get a reading (any reading) you cannot use both chargers at one time unless you disconnect the jumper between the two batteries. If you don't have an ohm meter or know how to use one, then just disconnect the jumper and charge away.

Very interesting Silvertip thanks for letting me know. Either way I think I'd be more comfortable disconnecting the series link for this by the sounds of it. Again thanks for your expert input

 

[bruceb58]

Re: Charging batteries in series

Buy a 2 bank battery charger like Silvertip said. They are pretty much all set up for charging a 24V(2 in series) set up. You can download the manuals off the website of the charger manufacturers to be sure before you make your purchase.