Thank you for the detailed reply. Much appreciated.
I have this set up on a boat with lithium domestic bank and AGM start bank (both 24V nominal). The AGM batteries are old and need to be replaced (working on that). But I have a question about the ācurrent limitingā happening in the Multiplus. Iāve had a 10A fuse on the trickle charge circuit blow (twice). The fuse is good quality, the fuse holder is good quality and looks fine (no heat damage). Some experimenting has shown the trickle circuit to put out as much as 7A, immediately after the engine stops running. So Iām wondering what is actually doing the ācurrent limitingā in the MP? The manual says this current is limited to 4A (but my amp clamp meter says thatās a lie). So.. is -anything- actually limiting this? If the house battery is lithium, sitting at say 28.6V, and the start is AGM (in poor condition, sitting at say 25.6V)ā¦ is the MP going to try to push higher amperage over the trickle circuit?
Fantastic post, covers everything and told me all I needed to know. This should be included in the Multiplus docs. Thanks for making it!
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So with a multiplus 2 it is always on regardless of if you turn it completely off with the switch underneath?
On a side note if we leave our van in storage for a few weeks, would you turn it off by the switch underneath or just turn to off in the VRM?
Thanks
As far as I know the trickle charger is always live because it is powered direct from the incoming DC. The reason I can not categorically confirm this is covered in the second answer, I never use that switch and now I have lithium house batteries and no longer use the trickle charger, I have added a standalone trickle charger available in the UK from Ablemail which can be programmed for lithium house batteries.
My physical switch is left on and I use the Cerbo GX or VRM on my phone to switch it on and off.
Thanks for this excellent write-up, @pwfarnell! I used it when determining how best to set up my DIY Node-RED Multiplus Starter Trickle Charge controller.
I have a Multiplus 24V 3000VA unit. Use the 24V trickle charge for the Generator starter battery top up, but it easily blows a 5A and 10A fuse on Gen start up. 20A seems fine but seems a bit of an overkill for a 4A limited charge current? Wondering if a 5A or 10A slow-blow would work? Any ideas?
If the generator start battery terminal voltage dips very low then I can understand the much higher current. Do check that you have a good connection between the battery terminal and the battery lug because a poor connection here will result in a lower terminal voltage. Remove the terminal and clean it and retorque it to get a good connection. It may also be a symptom of a too small or too low CCA starter battery or a failing one. A slow blow fuse may well be beneficial.
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Many thanks for that pwfarnell - the battery is only a couple of years old and is well fitted, but has always had a slow discharge issue, so will be checking if there is a leakage current in case that is indicating some fault that might be affecting the issue - its the same when isolated but has a simarine monitor upstream. I will re-check the torque too.