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Renogy 12v DC-DC Chargers in Series?

jsmit209

jsmit209

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Nov 24, 2022
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I had originally planned to go with a 12v system in my van. After some feedback, I'm now thinking about stepping up to 24v to safely use my 3000W inverter.

I have 4x Ampere Time 12v 200ah batteries with 100a BMS on each. I also have a Victron 100/50 MPPT solar charge controller and two Renogy 12v 40a DC-DC chargers.

If I'm thinking about this correctly, I could wire the batteries in 2s2p for a 24v battery bank. The Victron can handle 24v output. My concern is charging from the alternator.

Can I wire the two Renogy 12v DC-DC chargers in series to output 40a at 24v? If so, how? Also, my alternator in the Promaster is 180a. Would this be too much draw for the alternator to handle?

Thanks!
 
No. First, it's just a bad idea.

Second, if you look at the wiring diagrams, the (-) on both sides are bonded to the chassis. You can't do this with the charger with (-) connected to the middle of the bank.

Why not get a 12/24 DC-DC charger? Victron makes a couple.
 
sunshine_eggo said:
No. First, it's just a bad idea.

Second, if you look at the wiring diagrams, the (-) on both sides are bonded to the chassis. You can't do this with the charger with (-) connected to the middle of the bank.

Why not get a 12/24 DC-DC charger? Victron makes a couple.
Click to expand...
I think he has 2 of the isolated version.
Agree its a bad idea though
 
TomC4306 said:
What did he say that makes you think that?
Click to expand...
The 40 dc2dc charger is isolated.
I think he has 2 of these.
www.renogy.com

12V 20A/40A/60A DC to DC On-Board Battery Charger

Charge your secondary batteries on-the-go with Renogy's 12V 40A DC-DC On-Board Battery Charger. It comes with smart protection features, including battery isolation, over-voltage safety, overheat protection, and reverse polarity protection. Order yours today.
www.renogy.com www.renogy.com
 
Last edited:
John Frum said:
The 40 dc2dc charger is isolated.
I think he has 2 of these.
www.renogy.com

12V 20A/40A/60A DC to DC On-Board Battery Charger

Charge your secondary batteries on-the-go with Renogy's 12V 40A DC-DC On-Board Battery Charger. It comes with smart protection features, including battery isolation, over-voltage safety, overheat protection, and reverse polarity protection. Order yours today.
www.renogy.com www.renogy.com
Click to expand...
That is correct
 
jsmit209 said:
Any particular reason?
Click to expand...

Some reasons:

Chargers that aren't designed to charge as part of a series string don't tend to work reliably. There are dedicated chargers common in marine applications where 24, 36 and 48V banks are solely charged by chargers intended to charge 2, 3 and 4 12V in series. They are generally not charged by any other source due to the next issue.

With the potential to charge at different rates, they may imbalance the bank. As a result, any 24V charger may take one of the 12V elements out of range.

There's a risk that they'll outright damage each other. Since they're isolated, it's not likely, but I'd hesitate to run the risk.
 
For me the same reason that some 12 volt batteries are impermissible in series. Ie. renogy batteries. The electronic stuff inside is not rated to take the higher voltage. If it were I think renogy would probably sell those chargers as 12/24 volt DC to DC chargers
 
Consider that tuition. Maybe you can get back some $ on eBay.

Or, if you insist, make sure you take pictures and share them here.
 
If they are fully isolated they will be fine if charging half the 24v bank each, in fact we have been doing this in the marine boating world for a long time, I'm not talking about connecting the charger's + to - to make 24v combined charger, but connecting one charger to one 12v battery, the battery series connection will not affect the two separate chargers from working as long as they have isolated imports from outputs, this is why they have stated it is an isolated charger.
 
Hardergamer1 said:
If they are fully isolated they will be fine if charging half the 24v bank each, in fact we have been doing this in the marine boating world for a long time, I'm not talking about connecting the charger's + to - to make 24v combined charger, but connecting one charger to one 12v battery, the battery series connection will not affect the two separate chargers from working as long as they have isolated imports from outputs, this is why they have stated it is an isolated charger.
Click to expand...
Not sure I follow... Wire one DC-DC charger to each parallel pair of batteries?
 
Last edited:
Hardergamer1 said:
If they are fully isolated they will be fine if charging half the 24v bank each, in fact we have been doing this in the marine boating world for a long time, I'm not talking about connecting the charger's + to - to make 24v combined charger, but connecting one charger to one 12v battery, the battery series connection will not affect the two separate chargers from working as long as they have isolated imports from outputs, this is why they have stated it is an isolated charger.
Click to expand...
Hmm.
Okay, not where my head was at.
I would worry though about the series pair getting out of balance over time from slight differences in the two chargers.
Seems like a kludge to me.
 
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