Installing DC-DC Charger - Want to be able to combine batteries

[abarrow]

I'm in the process of installing a Renogy DCC50S. These DC-DC chargers allow solar input as well as charging from alternator/shore power.

In my case, and per the installation instructions, I have the alternator/shore charger output going to my engine start battery, with the output of that going to the Renogy, which in turn charges the house batteries.

All well and good, but... The problem is I still want to be able to connect my engine and house banks temporarily on that rare occasion that my engine battery doesn't get charged sufficiently to start the engine.

I certainly don't want to connect the input to the output of the Renogy - that might let the smoke out!

So, at this point, the best I can figure is installing a high current SPDT switch in the output of the Renogy that connects normally to the house bank in one position, but connects the house battery to the engine battery in the other. This would leave the output of the Renogy open.

Does anyone know if these devices care if the output is disconnected for a short time while I'm combining batteries to start my engine, or can you think of another way of doing this?

[coopec43]

I blew up the MPPT controller when I connected the positive solar panel cable to the controller. I should have read the installation instructions shouldn't I and connected the battery first.

I've now bought a couple of cheap switches so I can isolate the panels when I might want to disconnect the battery. (They were about $A6 each)



Here is a link to a thread which may help.

https://www.solarpaneltalk.com/forum...-to-controller


Wiring for MPPT solar controller with battery charger ...

https://forum.solar-electric.com › discussion › wiring-fo...
5 Oct 2019 — My first crack at a wiring diagram looks like (ignoring fuses/breakers & grounds for ... MPPT controller and battery charger + leads connected [somehow, pending ... When the fridge wants to run, the inverter wakes up to run it.7 posts · With two batteries often at different states of charge, I'd likely use a separate controller ...

Battery wires to MPPT controller — northernarizona ... 12 posts 17 June 2017

How to best wire multiple charge controllers to batteries ...24 posts 15 Mar 2018

Howto disconnect battery bank — northernarizona ...13 posts 4 Sept 2011

Two MPPT controllers serving one battery bank ...25 posts 30 Apr 2015

[abarrow]

Well darn. I guess I better start thinking about another way of doing this - or just set them up so I can't combine them. I hate that, but I also hate smoking equipment...

[tkeithlu]

For that very occasional situation of needing to use batteries from another bank to start the main engine, I use jumper cables. Low tech, indeed, but it leaves open options of combining any combination of the house, engine, and genset batteries without having to scratch my bald head over wiring.

[abarrow]

There's a lot to be said for KISS! I think the challenge remains to ensure the solar charge controller / DC-DC charger is disconnected so that it isn't damaged by alternate connections.

Perhaps I'm overthinking this. If I frequently have to combine batteries to start the engine, perhaps I need to look at the root cause of that issue!

[Culwatty]

Originally Posted by abarrow

I'm in the process of installing a Renogy DCC50S. These DC-DC chargers allow solar input as well as charging from alternator/shore power.

In my case, and per the installation instructions, I have the alternator/shore charger output going to my engine start battery, with the output of that going to the Renogy, which in turn charges the house batteries.

All well and good, but... The problem is I still want to be able to connect my engine and house banks temporarily on that rare occasion that my engine battery doesn't get charged sufficiently to start the engine.

I certainly don't want to connect the input to the output of the Renogy - that might let the smoke out!

So, at this point, the best I can figure is installing a high current SPDT switch in the output of the Renogy that connects normally to the house bank in one position, but connects the house battery to the engine battery in the other. This would leave the output of the Renogy open.

Does anyone know if these devices care if the output is disconnected for a short time while I'm combining batteries to start my engine, or can you think of another way of doing this?

I may be wrong,

But I am sure that specific B2B prioritises the start battery with the solar, so unless excessive cranking was required you should be fine.

As an option a backup you could simply have a changeover switch that feeds the power to the starter from start battery or house bank.. just make sure the power from the alternator stays separate. (This is if the renology switches the live not the negative)

[Stu Jackson]

Originally Posted by abarrow

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but... The problem is I still want to be able to connect my engine and house banks temporarily on that rare occasion that my engine battery doesn't get charged sufficiently to start the engine.................
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Why would you ever want to do that? The worst thing you can do is to combine a good bank with a dead one. Besides, start banks rarely get drawn down because starting an engine, even with glow plugs, only uses 1 or 2 ah.


If you simply switch banks completely it appears you have no issue.

[Thumbs Up]

A 1-2-both battery switch with make before break feature.https://www.amazon.com/BATTERY-SWITC.../dp/B005FD2PR8