AGM Battery Voltages

[MikeT6]

Morning all!

I’ve recently installed a CTEK D250SE with 120ah AGM battery in my van.

I’ve also hooked up a BM2 monitor to track the voltage etc.

It would seem that I’m charging at just under 15v, from what I’ve read this is normal.....

After turning the van off this obviously drops and after around 3/4hrs it drops to a level of about 12.45v...... is this acceptable?

From what I’ve read this seems a little low but am I over thinking this?

The BM2 suggests that the battery is sitting at about 73%.

Mike

 

[mmi]

Hmmm... as long as you see with D250SE charging voltage to be approx. 15 Volts it just means the battery is still gladly accepting charge which means it's not fully charged. Generally the threshold between absorption and float charging states is targeted to be at approx. 80% of full capacity.


EDIT: need to self correct a bit - after reading the footnotes of the graph.

STEP 2 BULK - Charging with maximum current until approximately 80% battery capacity.​

STEP 3 ABSORPTION - Charging with declining current to maximize up to 100% battery capacity.​

Anyways, seeing approx. 15 Volts means only that battery is still charging.

 

[Dieseldonkey]

I've got a similar concern with my Ablemail. The BM2 shows a typical day for me. Webasto starts up hence voltage drop at 0430hrs. But when I start the van up, I'm showing a charge voltage of only 13.7 volts from the DC DC charger. My understanding was 14.4 to 14.7 volts for an AGM was optimal. Yet when I plug the van into the mains and the Victron charger starts, its sitting at 14.95v. Resting voltage also drops down to 12.45v over the course of the day. Albeit the ambient temperature is around zero degrees. Anyone else with an Ablemail able (pardon the pun) to concur that their unit behaves the same way. Ta

 

[Taylorm]

Where did you connect the negative terminal for the BM2? I read that the negative shouldn't be connected to the battery, but should be to the chassis ground. The wire of the BM2 isn't that long. Interested to see how you've connected this. Cheers

 

[Higgidav]

I've got a similar concern with my Ablemail. The BM2 shows a typical day for me. Webasto starts up hence voltage drop at 0430hrs. But when I start the van up, I'm showing a charge voltage of only 13.7 volts from the DC DC charger.

I have an Ablemail and it’s exactly the same as yours sitting around 13.7v

 

[MikeT6]

Where did you connect the negative terminal for the BM2? I read that the negative shouldn't be connected to the battery, but should be to the chassis ground. The wire of the BM2 isn't that long. Interested to see how you've connected this. Cheers

My BM2 I sure showed to connect at the battery. But because I’ve used some fancy terminal covers I had to cut theplugs off and strip the ends back slightly. But yes seems to work fine with both + and - on the battery.