Charging a 120V DC battery bank

Saipro · January 2016

I know, it's a quite unpopular topic and so much has been written on it. This however is my version.

So a friend approaches me to help with his own inverter system. He's got one of those funny 120V DC inverters looking like a safe powered by a 120V 200Ah bank (pun intended). He wants to go green and opted for solar. I have been trying to use a single CC but seems I might fail in that quest as I can't lay my hands on a capable CC of repute. I have considered using two Midnites and the "follow-me" feature. I can't import Midnites in time to meet the project deadline. My options are restricted to the EP Solar iTracer 60A, MorningStar 60A and (reluctantly), the Outback FM 80. I won't use more than two CC and would rather avoid the FM 80. I did see a Fangpuson 80 (FM 80 clone) too.

Saipro · February 2016

I'm yet to solve the problem and I haven't been able to lay my hands on a Midnite Classic 250 KS. Prpject has been suspended but might be reviewed at any time. I want a simple solution, that's all.

Raj174 · February 2016

Midnite Solar may have one available, here's the contact email address. garagesale@midnitesolar.com

MarkC · February 2016

Saipro said:

I know, it's a quite unpopular topic and so much has been written on it. This however is my version.

So a friend approaches me to help with his own inverter system. He's got one of those funny 120V DC inverters looking like a safe powered by a 120V 200Ah bank (pun intended). He wants to go green and opted for solar. I have been trying to use a single CC but seems I might fail in that quest as I can't lay my hands on a capable CC of repute. I have considered using two Midnites and the "follow-me" feature. I can't import Midnites in time to meet the project deadline. My options are restricted to the EP Solar iTracer 60A, MorningStar 60A and (reluctantly), the Outback FM 80. I won't use more than two CC and would rather avoid the FM 80. I did see a Fangpuson 80 (FM 80 clone) too.

Similar quest with similar results - could not find a Midnite KS250, which is likely OK as apparently they were not reliable. I'm not about to stack MPPT CC's either. Moving on.

boB · February 2016

Midnite 250KS's aren't available anymore and I would advise against it. Actually there are still a lot of them working just fine, but...

Using two (2) MPPT charge controllers, one on each 1/2 or 60V part of the 120V battery bank does work nicely though. HOWEVER, you can't tie the two negatives together. The top half, 60V to 120V CC will have to be separate. Also, you won't need any Follow-Me connection because the two battery halves are independent and will not necessarily be the same state of charge to go from Absorb to Float together. This 2 CC method should actually be much better for your batteries anyway because they will stand a much better chance at not becoming unbalanced.

Common negative RS232 communications is not as easy for the two halves of the CC's either unless you had an isolator for that BUT if you were to use Classic CC's, they have an Ethernet connection which is already isolated via internal transformers in the RJ45 jacks.

Each controller would need its own PV array as well. IT would be advisable also to disconnect the internal MOV surge protectors from the top controller. This would be true for not only the Classic controller but the Outback and probably others as well. This is because the MOV can conduct from PV+ to chassis ground on the top controller and usually the castings/chassis of both controllers might be connected together. Also, the internal ground fault protection will not be usable on the top controller.

BUT, two CC's can do a good job of handling a 120V battery bank. I have seen it done many times, usually with the Outback controller, many years ago. A lower voltage charge controller will usually be rated for more current than a single CC like the KS that worked at 120V battery.

boB

Saipro · February 2016

Thanks Bob. Sounds like a headache. I love challenges but ..... Just like MarkC, I think I'll pass on this one - until sucha time as I encounter a scenario I can't evade.

Charging a 120V DC battery bank

Comments

Categories