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Rodeo Driver · 12-15-2020, 08:44 AM

We have a 2011 M2 chassis and I replaced the old Interstate brand house batteries with AGM V-Max to give us (considerably) more amp hours when dry camping. I noticed by looking at the Reolgy charge monitor that the house batteries aren't charging while the coach is running (charge monitor shows 80% or higher house battery charge) I did see a post (can't find it now, grr) Some time ago referencing a solenoid or something similar fastened close to the chassis batteries that monitors or directs charging to the house batteries when needed while driving. So I guess two questions; 1. Are the new house batteries with higher amp hours not yet at a low enough charge level while driving to allow this solenoid to engage and charge them? 2. Is there a solenoid or similar located close to the chassis batteries to check out?

kenwyatt · 12-15-2020, 09:28 AM

Can tell you how my 06 works. My system has a B.I.R.D relay and a Big Boy relay. It’s used to link both banks together to charge everything either off the alternator when driving or the charger when on shore power. Basically the B.I.R.D relay pulls in the Big Boy so you will see the same voltage on both banks. It’s almost how the boost works to start when your chassis batteries are low. What I found on mine 1 time when the chassis batteries went down was there is a 5 amp cb that sends sensing voltage to the relay that controls that. Reset the CB and all works now. All of that is located in the engine compartment in a large box with CAUTION signs all over it. Hope this helps.

twinboat · 12-15-2020, 04:02 PM

Most of the isolation/charging systems are voltage sensing now days. Like the BIRD in the last post.

The voltage sensing control looks for charging voltage from the alternator. If it sees 13.3+ volts, it sends a signal to the large solenoid to close it, connecting the battery banks together. They all charge.

Some my stop the charging after an hour if the house batteries are up to 13.3 volts, but that's not your case.

The large solenoid is often the cause of your problem. The internal contacts burn and don't conduct the charging current.

Test voltage on each side of the solenoids large posts. One side should be house battery volts and the other side should be chassis volts.
Start the engine, let it run 10 minutes, and test again. Both sides should be equal.

Bsipe01 · 12-15-2020, 06:01 PM

Using your DMM, measure DC volts across both of the large (battery connection) terminals on the charging relay. If it reads -0- volts, the relay is energized and has closed the circuit between the chassis battery and house battery. That it's reading -0- indicates that there's no potential between the two points, e.g. there is no voltage difference. If it reads 12V plus, then the relay is open, not energized, and not charging. Reading across a relay or any closed switch, breaker, contactor, etc. does double duty; it tells you if it's open or closed, and if it's closed, tells you if the contacts are impressing a voltage drop. -0- volts is a good connection, anything else indicates a closed relay but will indicate the amount of voltage drop across the relay. It's a troubleshooting shortcut that comes in handy.

FIRE UP · 12-17-2020, 10:42 AM

Quote:

Originally Posted by Rodeo Driver

We have a 2011 M2 chassis and I replaced the old Interstate brand house batteries with AGM V-Max to give us (considerably) more amp hours when dry camping. I noticed by looking at the Reolgy charge monitor that the house batteries aren't charging while the coach is running (charge monitor shows 80% or higher house battery charge) I did see a post (can't find it now, grr) Some time ago referencing a solenoid or something similar fastened close to the chassis batteries that monitors or directs charging to the house batteries when needed while driving. So I guess two questions; 1. Are the new house batteries with higher amp hours not yet at a low enough charge level while driving to allow this solenoid to engage and charge them? 2. Is there a solenoid or similar located close to the chassis batteries to check out?

Well Rodeo Driver,
I don't have a clue as to what an "M2" chassis is, who makes it, and what its details are. But, this is why I emphasize to either new coach owners or, new owners of older coaches, to try and learn as much about even some basics of their coach right after they get them. Now, not everyone is mechanically inclined and wants to learn about them. I can see that. But, having one of these rolling Kleenex boxes and not knowing even some basics, can, and often does, cause heart ache when even a minor break-down happens and you're away from home.

So, with all that garb being said, I'd find out, maybe from other "M2" owners or, a factory that puts out those "M2" chassis's or, maybe even some techincal literature that might be available on line, just what's involved in the charging of BOTH SETS of batteries on your coach. And that means BOTH charging systems. By both I mean, we all know an engine alternator charges the chassis batteries but, how does it link to the house batteries? And, how does your coach, when it's plugged into shore power, charge your house batteries and, if it does, how does it charge your chassis batteries?

Not all coaches are built the same. They all don't have the same components for charging. The end result is, you want ALL your batteries fully charged when you end up at a camp spot. But, how they get that way, can be quite different from coach to coach. Good luck on your endeavor to find out your issue.
Scott

jelag · 12-20-2020, 05:36 PM

One of the big problems with most Freightliner Chassis is that they use a Delco Alternator with an internal regulator... Not one controlled by the ECM...

Mine uses a 160 Amp Delco but the charging voltage is limited by the alternator to no more than 13.8 or so....

So if you get up the morning and your batteries are low... the charging system kicks in and brings the charge level up to 13.8.... as most of you have noticed that if your on shore power or on your gen set.... the inverter/converter usually starts the charge voltage at 14.2 or 14.3 and as the batteries take on a charge it drops to about 14 or so.... this higher charge voltage allows the batteries to charge faster...

If we drive down the road for 4 to 6 hours at 13.8 the chassis batteries are at maybe 80% the house batteries are at 65% to 70% and they won't get fully charged... this of course is because the lower charging voltage will only charge batteries to about 80 to 85%.... this is cool for a dump truck or a Semi with just 2 batteries but when you have a set of coach batteries that started the morning at a lower state of charge and you want to go into the night with a 90% or 95% state of charge, it's just not going to happen....

Even as we move into the newer vehicles and the ECM controls charging... the ECM has no clue there are some extra batteries that need to be charged... than add to this... the constant drain or lower voltage as the alternator tries to keep the inverter going and the lights on the Microwave, TV, and other stuff with remotes going..... that's usually 2 to 5 amps... 120VAC which is 20 to 50 amps DC....

It would be nice if you could adjust the regulator on the alternator or in the ECM and tell those devices we've got this whole other panel of batteries to charge .. up....

twinboat · 12-20-2020, 06:49 PM

Delco internal regulators are avalable in different voltages.

Check DB Electric, some are listed at 14.8 volts.

There are also 3 stage external regulators out there.

PS: You don't need to push 14.+ volts into a battery to fully charge it. It just takes longer at lower voltage. That and I don't draw my chassis battery down to 80% SOC.

DYNAMAX XL · 12-22-2020, 08:47 AM

I would not recommend mixing battery types .IE: Lead acid with AGM etc.
They have different charge rates and voltage characteristics

Rodeo Driver · 01-08-2021, 10:10 AM

Sooo, first or all, thanks for all the responses, they really helped me think thru this. I finally found the ambition to investigate in the cold. ( mine’s inside but not heated - that fix is coming) As it turns out, a loose, corroded cable was the culprit. I made a new cable and system charges as expected- thanks again for all the input.