Dual battery relay issues

Evening all. Got the second battery wired up today, but got some issues if any one can shed some light. All seems fine, both batteries seem to be charging, but I have 2 problems. 1) The engine management light has come on, 2) The split charge relay starts to click when you rev the engine. Any one had this before?
Cheers


www.clsdoncaster.com/my-blog

Hi Lambert, I'm at work so can't do much, however, on this link there is a diagram (at the bottom of the page when you open it)
www.clsdoncaster.com/post/jimny-with-a-c...ing-a-second-battery
This is how I've wired it. Charges fine on tick over, but you can hear the relay going nuts when you apply revs.
Cheers

Hello,

I used a Victron Energy Cyrix Relais to avoid this. They have a time lag for connecting or disconnecting the batteries based on the voltage and there is a D+ connection To the Cyrix to make sure that the alternator charges before the batteries are connected.

In my case, I connected a 40Ah LiFePo4 as primary battery and the lead acid as second battery. This works with the Cyrix-Li-ct.

I attach some pictures, including the plug where I got the D+.

This is not too expensive and works nicely. Hopefully this might help you.

Thanks RainerK, don't want to be buying new bits if I can help it. This build is new parts only when I need to, rest is stuff out my garage! This was a relatively cheap (and I assumed simple) kit, just need to know if it is normal behavior or if I have done something stupid (again!)
Cheers

Ok, then I cannot help you with hands on experience.

What I think happens is:

Something makes your relay close at under certain conditions - from what you write I would expect that this is based on the voltage of the main battery.

If the voltage gets over e.g., 14V the second battery is connected.

As soon as the second battery is connected, the Second battery starts charging and voltage drops below 14V because the second battery is not full.

The voltage drop makes the relais open again.

Then there is another round.

To prevent this the controlling of the relay would have to be adapted in either of 2 possibilities:
Either a time lag so that there is some time before the connection is opened again after closing this gives the second battery some time to charge. If this time lag would be 60 seconds, then the relay might switch on and off 20 times until the second battery is charged again. Or a bigger difference between the voltages that close and open the relay, e.g., close at 14V and open at 12.5V. In this case you would have to measure the actual voltages of your car with an empty second battery.

Or you do it manually with some switch. As soon as the main battery is charged you connect the second battery and disconnect it again after it is fully charged. This might be the easiest and cheapest solution - just do forget to disconnect when you turn off you car and run the fridge connected to the second battery over night.

Generally, make sure that the ampere rating of your battery connection relay is somewhat higher than the maximum ampere of the alternator because After connections the second battery there is not only the Energy of the alternator but also some from the main battery.

I hope this helps you a little.

Thanks, will have to look at some sort of delay if I can, don't want to go down the route of manual switching, I'll forget. The relay is 200amp, so should be more than sufficient for this purpose.
Cheers

Hi - quick update. Finished work and turned Little Jim on and let it sit on tick over for half an hour. Went to check on it, and it now there are no clicks from the relay. Can rev it gently, of harshly, and there is no noise. So my theory is, the batteries have now equalized, or the 2nd battery has stopped charging!! Still doesn't explain the EML being on. Unfortunate coincidence?