Leisure batteries not charging off alternator - maybe

[SimonM]

Alongside my 220w solar panels to charge my leisure batteries I have a Victron Energy Cyrix-CT relay unit that is supposed to send a lot more amps from the alternator when the engine is running.

Today I noticed that it doesn’t appear to be working, but I don’t know quite how to prove it. I think I also noticed it not working last time we were away for weeks on end, but I forget.

Previously, when my leisure batteries have been low, next morning after a lot of TV useage, I could easily see 25 -30 amps or so making their way into the LB’s and fully charged in a few short hours.

Today, the LB’s were showing 80% charge just as we were about to return home after a day out and a few hours watching F1, the display had been 100%. I turned on the engine and saw nothing going in other than the 2a showing from the solar panels.

By the time we got home 40 miles later my display showed only 81%.

So, if there is perhaps a fault in the relay how do I prove it?

 

[colinm]

Have you checked the actual voltage of your batteries? If you % meter is one of those which monitors input/output it may be that the relay is bypassing it.

 

[SimonM]

My BM-2 monitor means I can see both LB and Starter batteries individually. They’re at 13.8v now as there is a solar charge going in of about 2a as it’s nice and sunny at home & now showing 84% charged.

I can go and have a better look tomorrow at home, but if there is no charge from the alternator apparent then I’d just like an idea what to check out - multimeter in hand.

 

[SimonM]

With everything switched off the relay feels warm to the touch.

First thing this morning it’s overcast and the solar is putting out very little. I removed the inline fuse from the controller so no solar power was now going through the system.

I started the engine and there was no great amperage showing on the battery monitor, maybe a couple of amps. Both leisure and starter batteries were then showing 14.4v and being charged by the alternator. But how much I wonder?

So the next question is whether the alternator is working correctly or is it the relay at fault? No idea, suggestions?

 

[Thistle]

The BM2 is a great little gadget, I have lots of them!
If you are seeing 14.4v at the chassis battery with the engine running then allowing for a bit of volt drop you should see similar at the leisure battery end as well. You should also see a clear step in the bm2 graphs as the voltage increases when you start the engine.

If you suspect the relay measure the volt drop across the input and output terminals if it’s getting hot due to internal resistance there would have to be a noticeable volt drop on the terminals