Some New Battery Questions

[GallenH]

I’m trying to get some understanding of the electrical system in my 1997 PW. They have a schematic of what they call the main 12v system in the very skimpy manual. So, here are several observations/questions:

1. The engine alternator (there’s only one) goes to an isolator which sends one out to the chassis battery and the other through a 40A/12v breaker to the cabin battery positive. So it charges both the chassis and cabin battery. But there doesn’t appear to be anything controlling the amount of charge. Can the cabin battery overcharge?

2. A second wire connected to the battery positive goes through a 30A/12v breaker to what is labeled the controller and appears to be both the 12v power distribution center and the convertor for incoming 120v shore power. It must be that it not only receives power from the battery (for distribution to lights, etc.) but also can send 12v power back to the battery from the convertor to charge the battery. Given its age is it safe to assume that it’s a fairly primitive charger and not a 3-stage? I’ve squeezed a 100AH LifeLine AGM into the (single) battery box and, given previous advice you’ve given me, want to make sure it’s being charged as well as possible.

3. A third wire connected to the battery positive goes through a 15A/12v breaker directly to the Dometic fridge. Since it’s an old fridge it does not have any circuit board (or auto light, etc.) so I’m assuming that this is only for the 12v heater element when the fridge is on 12v. There is a 120v outlet in the fridge compartment where the 120v line from the Dometic is plugged into.

4. I’d like to do 2 things with the cabin battery and I’m trying to figure out the best way to do them. First, the battery has no disconnect. I’ve been taking off the (multiple) negative leads to the battery when I put the RV in storage. Second, I’d like to add a better battery monitor. I’ve been looking at the Victron. Given the nonexistent room in my battery compartment, I’ll probably have to mount the shunt somewhere outside the box along with the switch. So the route would be: cable from battery negative —> shunt; cable from shunt —> CO switch; cable from CO switch —> multiple negative leads (probably with a terminal bar in the battery compartment. Does this appear ok? It does have the issue of leaving the Victron shunt active, even in storage. Another alternative would be to have the CO switch pre-shunt in the circuit.

Thanks in advance for any advice/comments!

Glenn

[Sehc]

I use bus bars. that would reduces the connections on the battery terminal to one cable. The disconnect switch could be on the positive. battery pos to switch to pos bus bar. Then the negative could be battery negative to shunt to neg bus bar. If you don't get a switch, you can disconnect one negative at the battery.
I don't trust RV converters. I much prefer separate 120 volt charger. My choice are ProNauticP by ProMariner.
I have the bus bar 3 feet from the battery, so battery positive terminal 300 amp fuse and smaller fuses on the bus bar for the charger and inverter, as well as a fuse panel for smaller loads, such as fridge and water pump.

[Knit]

On question 1, it is likely that the house battery is charged to the same voltage as the chassis battery. So you are probably not overcharging.

On question 2, I recommend that you find a make and model number and then do some internet searches to figure out what you have. Maybe an earlier owner upgraded it. But if not you should for sure get a converter that has a setting for AGM batteries.

On question 4, I installed a Victron as well. I put the cut out switch on the battery terminal. Then went from the switch to the shunt. Then shunt to to chassis ground. Shunt is not powered when battery is disconnected. The cables to and from the shunt are the same size as the original cables and about 1ft long. I mounted the shunt inside the firewall because it is not weatherproof. My firewall luckily had an opening for other cables at just the right spot. Victron Bluetooth phone app is well done.

[GallenH]

Sehc and Knit: Thanks for your responses. I did check and my control center is original and doesn't vary charging voltage. Now looking at possible replacements. Best.glenn

[markopolo]

The Promariner ProNautic / Sterling Pro Charge look to have a nice feature set and temperature compensation but seems to completely lack advanced control or user control of ending amps / exit amps for the transition from absorption to float - just my opinion.

This complaint - ProNautic / Sterling 1240P Charger issue - Cruisers & Sailing Forums - says it exits very high, sometime at 20 or 22 amps! The battery is nowhere near charged. That's almost 10 times higher than what Lifeline recommends for example. (460Ah battery bank x 0.5% = 2.3A)

That causes the the end user to physically have to monitor the charge process and restart it etc.

The fix suggested here - ProNautic / Sterling 1240P Charger issue - Cruisers & Sailing Forums - again means that the end user is very much involved in the process and has to watch the current flow and stop the unit and reprogram when they're satisfied that the battery is charged.

The Lifeline battery manual recommends exit absorb when the current has dropped to 0.5% of the battery's capacity. That is 1/2 an amp on a 100Ah battery (0.5A).

Hopefully Sehc will share the charger capacity, battery capacity and ending amps or exit amps and he's observed if relying on automatic charging. Maybe there's a way match battery bank size with charger size to get the Promariner ProNautic / Sterling Pro Charge to exit the absorption stage at the current the battery manufacturer recommends.

[booster]

I agree with Marko, the Promariner/Sterling has some nice things including custom voltage ability, etc, but is missing one very big thing, controlling charge by amps.


I think all the Sterlings use their "super secret super accurate" algorithm that uses a variable absorption time based on measurements it takes during the bulk stage. I don't think it even uses battery bank amp hours as I didn't see a place to enter it with a quick look at the instructions.


The charging accuracy of algorithms can go anywhere from horrible to not so bad, depending on all kinds of external things like battery bank size, depth of discharge, loads on in the van, solar contributions, etc. They are locked in, so you get what you get, and the only way to tell how well it did is from a standalone battery monitor.