Oddball question about combining agm bank and lead acid

[dwh]

I have my doubts about that 11.4v the scanguage is showing you.

First of all, again - when the batteries are tied it's just one big bank. There IS NO "engine side/house side".

So if the batteries are tied and you light up the glow plugs, it would be pulling the entire combined engine and house bank down to 11.4v. NOT just the starter battery.

If it really did pull all the batteries down to 11.4v and you let it run for >4 seconds, the ACR would disconnect.

You also have to keep in mind that what happens on this circuit over here does not tell you what is happening on that circuit over there.

The vehicle's electrical system (fusebox) is separate from the ACR circuit. The glow plugs and the scanguage are on the vehicle's electrical system. Pulling down the voltage of the vehicle's electrical system does not mean that the battery has been pulled down to that voltage - just that that particular circuit (tapped off the battery) has been pulled down.


You need to take better measurements. Use a multimeter and check the voltage across the battery terminals when the glow plugs are on. That voltage will almost certainly be higher than the voltage that the scanguage is reading off the fusebox.

 

[Bear in NM]

dwh,

I was back at wiring this evening, and did the check you noted. Using my Fluke, I connected to the 1/0 wires at the big plug which is wired directly to the starter batteries. So not on the posts, as dropping takes a great deal of time and energy. So this was at the end of about 3 feet of 1/0, wired correctly across both start batteries. This is the plug that I use to join the start bank at the fuse/breaker panel I am wiring, before the Blue Sea fused bus bar.

Yup, the meter went to 11.5v with the key turned to glow plug start. The house battery bank was manually disconnected via the switch you helped me wire.

I was figuring the Scanguage II was probably reading correctly, as it is connected via the OBDII. When doing this startup sequence with the Scangauge showing FICM voltage, it reads 48.0, same as when operational. It also picks up other fields correctly, like engine temp, trany temp etc.

The batteries are brand new Interstates. I originally charged them with my good charger when I installed, and they appeared to good. I also noted this 11.5 voltage on the original batteries which were of unknown age, and "AAA" brand. This voltage, and the fact that I had no knowledge at the time of the age nor brand is what prompted me to buy two new batteries, right out of the blocks. That and the fact the person I bought it from said it needed a trickle charge all the time.

I am clear that when tied, they are one bank. I am also clear that I have several different circuits doing their thing on the start side, and I really do not understand the van's electrical system yet. I'll do more testing when I have a good day, and a clear head. Not going to manually combine for start, until I have a better way to measure amps.

Thanks,

Craig