12v to 24v Split charge relay

[hollyb96]

Hi, just looking for a bit of advice. I have a portable power station battery. I have 3 100w solar panels but in winter, it's not producing the power I need so I want to fit a voltage sensitive split charge relay to my van to power the van as I drive. The best way to do this I have found is to install a 12v to 24v step up converter along with the split charge relay as it needs to trick my power station into thinking 24v solar panels have been attached otherwise it will only delivery 12v to my solar input and less wattage. My power station is 2000w and accepts 500w, 11.5-50v and 20a through the solar input. My van battery will be changed soon to a 70ah and my alternator is 140a. Would this system work:

This split charge relay kit which uses 7awg cables, 60a fuses and split charge relay is 140a: https://www.amazon.co.uk/gp/product/B0D17CL4RS/?tag=mhf04-21

This is the 12v to 24v step up converter: https://www.amazon.co.uk/gp/product/B09F3J45FW/?tag=mhf04-21

After the 12v to 24v converter, add one of these 60a fuses to the cable: https://www.amazon.co.uk/gp/product/B0BSGC8CKC/?tag=mhf04-21

And then this 10awg cable to go from the fuse holder after the 12v to 24v converter to then plug into my battery: https://www.amazon.co.uk/gp/product/B0CZ68Z8GG/?tag=mhf04-21

Would that all work or should I change some things? I have attached a photo of the system. Thanks

 

[autorouter]

As you say, there are various methods to achieve charging of the power bank from the alternator. If you are doing it this way, then it should work OK. The fuse in the wire from the DC-DC converter to the power bank should be a lot less than 60A. The maximum current expected along that wire is 20A at 24V, so a 25A or 30A fuse is fine. The maximum current on the 12V side is 40A, so a 50A fuse would be OK. near the leisure battery. The fuse between the split charge relay and the DC-DC converter is not necessary, in my opinion.

 

[hollyb96]

As you say, there are various methods to achieve charging of the power bank from the alternator. If you are doing it this way, then it should work OK. The fuse in the wire from the DC-DC converter to the power bank should be a lot less than 60A. The maximum current expected along that wire is 20A at 24V, so a 25A or 30A fuse is fine. The maximum current on the 12V side is 40A, so a 50A fuse would be OK. near the leisure battery. The fuse between the split charge relay and the DC-DC converter is not necessary, in my opinion.

This is the updated one after speaking to someone on a different forum. I was using chatgpt for some of it and it said 60a. With this new system with the charger instead of step up converter. Do you still think 50a fuse would be better?

 

[autorouter]

A 60A fuse should be fine, less chance of blowing if there's a startup surge. I think the wire thickness on the 5m 12V 40A wire is a bit minimal, I would go at least one step up - 25mm2 would not be unreasonable. High amps 12V circuits need thick heavy wires, that's why anything bigger than a light van has 24V electrics. If you're sticking with 12V electrics then you have to shell out for the appropriate wires.

The idea is to keep the total voltage drop to about 3% or less. There is a voltage drop calculator here

Voltage Drop Calculator | 12 Volt Planet Cable Calculator

Use our Voltage Drop Calculator to select the correct Cable for your campervan, motorhome or boat wiring application. Cable Calculator for Auto and Marine Electrical Components from 12 Volt Planet - Cable Size Calculator

www.12voltplanet.co.uk

so you can play with the figures to give you the total voltage drop.

There is also an AWG to square millimetres conversion table on the same web site.

 

[hollyb96]

I just have a vw caddy maxi so not a big van. Its saying with 16mm2 cables, 12v, 15a current draw and 5m one way circuit length its drop is 1.57%. Would you say that it should be a smaller drop than that?

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[autorouter]

I just have a vw caddy maxi so not a big van. Its saying with 16mm2 cables, 12v, 15a current draw and 5m one way circuit length its drop is 1.57%. Would you say that it should be a smaller drop than that?

I was thinking the 12V current would be 30A, if the 24V output is 15A. That gives a voltage drop of 3.15%. That would just be OK if it was the only voltage drop but there are other bits of cable, so worth thinking about stepping up the thickness.

However if the chassis returns are good and solid then you'll probably be OK. The voltage drop along the chassis return path is usually quite low. So the total voltage drop won't be simply double the drops along the wire, as the calculator assumes.

 

[hollyb96]

The 12/24v charger is 15a so that means the current draw is 15a? Or am I wrong? I'm totally new to this haha
It will deliver 360w to my power station. When I put all that info into the the voltage drop calculator, it says 1.57% drop, unless I am doing something wrong