Split Charge Relay Questions

[wagohn]

Hello,
So I picked up a 200amp relay to help boost my solar house batteries on my 76 bus. Basically, the pictured relay connects the '+' terminals on my engine battery and house battery. The idea being that when the ignition is ON, the relay activates and the house battery is then being charged by the engines battery, which is being charged by the alternator. When OFF, the house battery is then isolated from the engine battery. However I had the following thoughts
* If I camp and completely kill the house batteries (a bank of two), when I go to start the engine, and the relay activates, could my engine not be able to turn over because the dead battery is now sucking in all the power from the charged engine battery?
* Wont I have to use "starter-thickness" cables to the relay because when starting the engine, and the relay activates, the starter is going to draw from the house battery too?
Thanks all, dont want to fry my bus

[ImAddicted]

Wire it off the oil pressure switch or the trigger wire for the alternator, that way they don't connect until the engine is running.

As for wire gauge, it isn't going to be drawing the huge, immediate amps that are required for starting, it is going to be pulling whatever amps are left over after the engine uses what it needs, your alt is either 55 or 70a, not the 500+ amps available for starter. I'm using 4ga on mine, but I've seen as small as 10ga used without issues. Just make sure you fuse both sides close to each respective batteries.
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1979 Transporter (sold)
KC1MUR

[wagohn]

[skills@eurocarsplus]

what gauge battery cables (or wires) are linking the main and the aux battery together?

from the factory if equipped with an aux battery the wires were light..like 12 or 14 ga iirc.

in the factory set up, the alt wire would close the relay once the bus started, therefore isolating the 2 batteries.

if you do it simply with a key on and the wires are not battery cables, you'll smoke the light gauge wires if one battery is dead.

you would be best to tap into the load reduction side of the ignition switch. that would eliminate any chance of the 2 batteries connecting during starter operation.
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[wagohn]

[ImAddicted]

[wagohn]

[busdaddy]

[wagohn]

[busdaddy]

[wagohn]

[zerothehero]

I prefer to use a voltage sensing relay to switch the bigger relay that connects the 2 batteries.

These switch when the car battery reaches 13V
They also have some handy switched & permanent connections.

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I like caves..
Caves are cool
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1979 Devon Moonraker 1600 twin port
1978 Oz Microbus 2000 FI Auto

[wagohn]

So I decided to go with 6 gauge wire after all, but a thought came to mind. 6 gauge is a thick wire, and it's recommended to fit inline fuses, how do I do that? Ive obviously worked with "regular" inline fuses for when youre fitting a stereo etc, but how do you fit a fuse to thick 6 gauge wire, and what amp?
Thanks all.

[BUSBOSS]

Have you seen the great product line from Blue Sea?

If not, check them out.

Here is a great thread. If you have questions, reach out as I just finished mine.https://www.thesamba.com/vw/forum/viewtopic.php?t=567016&highlight=blue+sea

Here are the type of fuses connections I recommend especially for engine compartment use where there is fuel/oil and spark:


https://www.bluesea.com/products/7720/AMI___MIDI_Safety_Fuse_Block
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All the redemption I can offer, girl, is beneath this dirty hood
1976 Westfalia
1970 Karmann Ghia Convertible (sold - but not forgotten)

[ImAddicted]

I used these, then the gauge wire isn't a factor.

https://www.amazon.com/gp/product/B06Y3QHPWB/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

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1979 Transporter (sold)
KC1MUR

[wagohn]

Thanks guys - just what I needed.