DC to DC charging toggle switch?

[tselliott]

I currently have a Renogy 20A DC-DC charger to recharge my dual (12v) battery setup. Is it possible to install a toggle to switch it from charging the existing second battery to a new third one? I recognize that if at all possible, it would be better to wire the 2nd/3rd batteries in parallel and just have one battery bank that the Renogy charges. So at this point the question is more is this possible and not is it recommended.

Thanks!

 

[0truck0]

Your reasons are your own and no one here will question why you need something, but will try to help you get there... lol, well, we will try to help anyway...

Sure you can. Do you want to do this switch manually or remotely (from a dash toggle switch)?

Look up solenoid switches. With these you can use a little dinky dash mounted toggle switch to power a bigger high amperage switch that carries your charging current.
There may be what you are looking for, but if not, you can get a toggle switch and two 20+amp relay switches. I know the smaller relays have Normally Open (off) and Normally Closed (on) options, but not sure about the big solenoid switches. It will say NO for Normally Open, NC for closed.
You wire it to NO or NC depending how you want the relay to work.
NO means that when the little toggle is not giving it 12v power that the solenoid is off and not letting current run. Wire each differently and when little toggle is off for NC version then power will flow through the big relay. So, wire both big relays to the one toggle. When toggle sends power, one big relay will be off and one on, because when one gets power it lets current flow but does NOT let power flow when it loses power.
Opposite for the other way, when it does not get power it lets current flow, but when it gets power it stops current from flowing.
So, if you have one of each set-up then you can send power to both and one will work, one will not, Stop power and one will not work, one will work.
This way only one set of batteries is connected to your charger. This happens on the positive wire side only of course.

Now, this is exactly how relays work, and relays are all over your vehicle and just look up how to wire them online rather than me butcher it.
Maybe you can get a relay that will take your 20 amps, or maybe you need get a big solenoid to do the 20 amps.
I just have not played with or know of a big solenoid that has options for Normally open/closed, but relays do have this...

Big solenoid ones:


Little Relay switches:

Actually, the middle bottom one looks like exactly what you need, already set up and described in picture for you. I got these pics off internet search results.

 

[mikefitz]

Is it possible to install a toggle to switch it from charging the existing second battery to a new third one? I recognize that if at all possible, it would be better to wire the 2nd/3rd batteries in parallel and just have one battery bank that the Renogy charges. So at this point the question is more is this possible and not is it recommended.

Whilst charging seperate is possible, if you intend to use the batteries in parallel as a single battery bank to power loads, then its advised to charge as one 'big' battery. Ensure the batteries are near the same voltage before connecting in parallel.

 

[0truck0]

No, most do not recommend wiring old batteries to new batteries, or any dissimilar batteries ,together in parallel. The bad one will draw from the good one and both will only be as good as the bad. However, you can do this if willing to accept the issues, I would not myself.
In series is different.

 

[cdoubleday]

Not sure if you got this sorted but to make it really simple. Think of it as a dual battery setup for your solar charger only downside would be they would have to be like batteries eg all lithium or all lead acid because the charge profile and arranged in same voltage configurations.
Hope this helps

I just re-ead your post and interpreted it differently.
Do you mean dual as in 2 batteries in parallel being charged from the controller?

I have the 50A variant setup in a 4x4 which runs a dual battery system off the alternator when both batteries are charged it switches to the solar charger alternator input and charges a lithium battery whilst continuing to charge from solar.
If the lithium battery is full it trickle charges the vehicles dual batteries.

In my example above meaning you could have two separate 12v lithium systems by running a dual battery setup off the solar charger.

wouldn't recommend it tho much better ways to design a system. For example halve your panels and get a second dc-dc charger.
pros - charge both systems at once, works independently, can have different battery combinations and voltages
cons - sacrifice charge power/time