Batter bank as a power source for solar charge controller

[riotbob]

Hi Everyone,

Need some recommendations/ advice.

I currently have a 12v 100ah power station with a renogy 40a mppt solar charge controller.

I would like to connect a 12v battery bank to my power station(PS) to extend compacity but they are not the same type of batteries as the PS. My thought is to connect the battery bank to the mppt as the power source to charge the PS. Will this work? If so, any concerns? The battery bank is a 12v 300ah, 3 x 100ah batteries connected in parallel. Thanks!

-RB

 

[cs1234]

Got any specs or model information on the power station?

 

[timselectric]

A 12v battery won't be a high enough voltage for a SCC to charge a 12v battery.

 

[riotbob]

Got any specs or model information on the power station?

What would you like to know? I built my power station, can't really provide model info. The battery is a 12v 100ah renogy battery.

 

[riotbob]

A 12v battery won't be a high enough voltage for a SCC to charge a 12v battery.

If I connect the 3 batteries in series to make it 36v, that should do it? Any concerns or considerations?

 

[timselectric]

If I connect the 3 batteries in series to make it 36v, that should do it? Any concerns or considerations?

That will work fine. As long as that voltage is in the range of the SCC.

 

[riotbob]

That will work fine. As long as that voltage is in the range of the SCC.

Got it. Thank you.

 

[sunshine_eggo]

If I connect the 3 batteries in series to make it 36v, that should do it? Any concerns or considerations?

Heck yes. The batteries can deliver ludicrous current. Definitely fuse the input to the MPPT.

You may also create a situation where the MPPT can operate at maximum power for an extended period of time. Most don't necessarily expect to deliver max rated power for several hours.

 

[riotbob]

Heck yes. The batteries can deliver ludicrous current. Definitely fuse the input to the MPPT.

You may also create a situation where the MPPT can operate at maximum power for an extended period of time. Most don't necessarily expect to deliver max rated power for several hours.

Cool!

About the max power, should I put some sort of resistance to keep it under?

 

[cs1234]

Be careful connecting batteries up to solar charge controllers, or anything really for that matter. I've found you want to connect it up initially with a pre charge resistor or you might blow something out in it.

 

[riotbob]

Be careful connecting batteries up to solar charge controllers, or anything really for that matter. I've found you want to connect it up initially with a pre charge resistor or you might blow something out in it.

Hmm, pre charged resistor. Ok, I'll have to check out how to do that. Thank you!

 

[sunshine_eggo]

Cool!

About the max power, should I put some sort of resistance to keep it under?

There's no practical way to do this.

Be careful connecting batteries up to solar charge controllers, or anything really for that matter. I've found you want to connect it up initially with a pre charge resistor or you might blow something out in it.

There are no caps charging on the PV side of the MPPT.

 

[riotbob]

There's no practical way to do this.



There are no caps charging on the PV side of the MPPT.

What if I put a dc to dc converter between the battery and pv side of the mppt?

 

[riotbob]

What if I put a dc to dc converter between the battery and pv side of the mppt?

Sorry, I meant dc to dc charger. Then again, if I am using a dc to dc charger do I really need the solar charge controller to be in the middle?

 

[timselectric]

What if I put a dc to dc converter between the battery and pv side of the mppt?

Now you're just making it more complicated. And adding failure points.
Just fuse everything properly and hook it up.

 

[timselectric]

Sorry, I meant dc to dc charger. Then again, if I am using a dc to dc charger do I really need the solar charge controller to be in the middle?

Nope

 

[cs1234]

There are no caps charging on the PV side of the MPPT.

I got a pretty nasty spark hooking up a 200amp 24v lifepo4 array to the DC/MPPT input side of a grid tied inverter with limiter. Left quite a nice little scorch mark too. Spark goes away if connecting it with a pre charge resistor.. so I just do it now with everything that I connect to a battery.

I figure it's an easy enough thing to do to everything DC to avoid any nonsense.

 

[timselectric]

I got a pretty nasty spark hooking up a 200amp 24v lifepo4 array to the DC/MPPT input side of a grid tied inverter with limiter. Left quite a nice little scorch mark too. Spark goes away if connecting it with a pre charge resistor.. so I just do it now with everything that I connect to a battery.

I figure it's an easy enough thing to do to everything DC to avoid any nonsense.

That's very odd, because the MPPT should perform a sweep (assessment) before it starts to draw any current.
(Unless it's already running from another input source)

 

[mikefitz]

Suggestion 1
Why not connect the 3 batteries in parallel to the existing power station battery ?
Suggestion 2
Your Renogy MPPT operating at full power for long duration may overheat.
Suggestion 3
If you have a 3 battery 12v bank, (presumably charged as a 12v bank), feeding the power station battery via a DC to DC battery to battery charger may be a more practical alternative.

Mike

 

[cs1234]

That's very odd, because the MPPT should perform a sweep (assessment) before it starts to draw any current.
(Unless it's already running from another input source)

I suspect it's because it was a grid tied with limiter inverter (GTIL). Even though it's an MPPT/battery input, no telling what it is doing with that DC once it gets it connected.

I actually had one of them blow a chip off the motherboard just recently after a power outage. I have it set on an AC circuit that stays off after a power outage until you manually restart the AC circuit, to avoid any possible feedback to the grid before I have loads running. The GTIL was off, but still connected to my battery array. As soon as I turned AC power back onto it's circuit, it went kapow and the magic smoke came out of it.

I don't think anything on it's AC side did it, but something on the DC side. I suspect it somehow shuts off the connection to the DC circuit when it loses AC power and upon reconnecting the AC it opened it back up having lost all charge in the caps. Since it was connected to DC with no type of pre charge taking place, it took everything the 200amp lifepo4 battery array was willing to give it. It tripped the 100 amp midnite DC breakers that are on each of the 2 paralleled 100amp 24v batteries when it did it.

To be safe, when I turn them back on after a power loss, I am now cutting off the main battery DC circuit first, turning AC back on so it powers up, precharging the GTIL DC circuit and then toggling the main battery connection back on. So far so good, but who knows.