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Renogy DC to DC Hack

RedneckRickem

New Member
Joined
Nov 25, 2021
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Just a little hack I figured I'd share with owners of the 50A DC DC charge controller. My current system consists of 3 175W panels, 2000W PSW inverter and the controller. I was a little bummed on how we're limited to 4-600W of solar for charging without running an engine to draw extra from the alternator. So what I am doing is adding a separate charge controller with 2-300W of solar to the starting batteries so when the engine is off the DC to DC controller will draw the excess from the start batteries thinking it is the alternater charging. I like to sit at anchor on my boat for extended periods of time so this will be a perfect way to add extra solar because Renogy controllers dont communicate with each other to add directly to the batteries.
 
Why not put the second controller on your house bank, and use the DCDC charger to keep the starting battery full.

Solar controllers do not need to communicate to do this. Having 2 solar controllers would be no different than one solar controller and a DCDC charger.
 
Why not put the second controller on your house bank, and use the DCDC charger to keep the starting battery full.

Solar controllers do not need to communicate to do this. Having 2 solar controllers would be no different than one solar controller and a DCDC charger.
DCDC controller is for house bank, second is for starting batteries. Engine off-controller charging start batteries will be adding to the DCDC controller. 2 separate systems. I dont think you know which DCDC controller I'm talking about. It takes charge from PV and Altenator. 2 controllers will not work with housebank cause without communication unlike the Victron, one will cancel out the other.
 
DCDC controller is for house bank, second is for starting batteries. Engine off-controller charging start batteries will be adding to the DCDC controller. 2 separate systems. I dont think you know which DCDC controller I'm talking about. It takes charge from PV and Altenator. 2 controllers will not work with housebank cause without communication unlike the Victron, one will cancel out the other.
Yes, i understand exactly. I've done it, and it works fine, even with solar controllers that don't communicate. Make sure then controllers are set up the same, and they will not cancel each other out. It is quite common to have multiple mppt controllers, even mixing brands.

As far as what each controller "sees" they can not tell if the other charger is solar, a dcdc, or an alternator. They are all chargers.

If they are set up very differently, they might not all change stages at the same time. But that is irregardless if 2 solar controllers or solar and dcdc. And makes only a small difference in charging.

I have done this using multiple brands of MPPT controllers, both generic, victron and generic, and both victron. Using Renogy dcdc charger, balmar duo charge, and even a simple combining relay to charge the start battery.

Its even quite common to have the alternator connected to the house bank so all charging goes there, with a dcdc charger or relay to keep the start battery charged.
 
sorry to post on old forum but just incase others stumble across this.

Not sure if the OP realizes that the 50A DC DC charger trickle charges the start battery through the alternator input.

As wholybee stated charges don't care about each other they only care about the battery voltage

Difference I see would be more power available to the start batteries initially until charged but then restricted to 25A, not to mention the dcdc on house batteries would be taking the full strain of the system, single fail point limited to 50A

Compared to trickle charge start batteries from the dcdc but allows for the alternator to input 25A which in doing so start batteries would be charged and you still get full charge from both solar chargers allowing 50A plus whatever your choice of A for 2nd charger if one fails the system will still charge
 
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I run two totally separate solar/MPPT systems into one battery. None of the smart parts care and the dumb part care even less. It all works.
I could not figure out what this guy was doing. Sounds like he is a boat guy, shoulda posted on the boat section.
Yes, he should just put the second solar system straight into his destination battery bank, and not try to mess with incorporating the DCDC charger which is hooked to the starting battery and alternator apparently.

Sometimes it is more fun to build a Rube Goldberg toy though.
 
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