Community Forums

PJW73NH · 06-07-2019, 02:32 PM

Greetings,

I flew out to Idaho last week form the east coast and am embarking on a trip back east with a 1997 Damon Intruder. 359. I've spent the last 5 days going over all the systems and everything is a "go" except I can't get the chassis engine (275 hp Cat) to charge the house batteries.

The chassis batteries charge at about 14.2 volts at idle. The house batteries appear to be unaffected by the engine alternator. There are 12 switches on the dashboard. Two of them have to do with the batteries. One is a momentary double throw switch. Pushing left clicks on the house batteries supplying 12 volts to the coach. Pushing the switch right, disconnects 12v from the coach.

The second one is a single throw momentary that I believe is the "chassis battery boost." That is, if for some reason the chassis batteries get too low to start the rig, holding this switch down while cranking the engine will use the house batteries to "assist" the chassis battery in getting the rig started.

Neither of these switches appear to have any effect on the "ENGINE" charging the house batteries.

Two important points.

1. Shore power will charge the house batteries
2. Generator power will charge the house batteries.

I've checked all the fuses and cable connections I can find, and nothing is our of line. I have the owners manual and the schematics, but they are rather vague. They meant for SEVERAL different configurations of motorhome.

Any assistance welcome.

Thanks

Paul... NH via ID....

twinboat · 06-07-2019, 03:07 PM

Find the solenoid that that boost switch controls. It may well also be your charging/isolation solenoid.

They have a history of failing internally, although still sounding like they actavate.

Have someone push the boost switch on and off and listen for it. It will have a large battery cable from each battery on the 2 large terminals.

MSHappyCampers · 06-07-2019, 04:40 PM

I'm not a mechanic but I think there are motorhomes that the alternator only charges the chassis batteries.

Jim_HiTek · 06-07-2019, 07:27 PM

In a '97 I believe you're going to find a large BCC (battery control center) near the batteries. That's where those big relays should be. There is a circuit inside that box that measures the voltages of the batteries. IF the chassis batteries are weak (doesn't sound like it with the 14V figure you mentioned) it will continue to charge them until they reach a charged threshold. Then the circuit will close the relay that is also used as the AUX start. This can take forever with bad batteries but typically just a couple minutes. Those minutes are when you should relax and wait before taking a voltage reading on the house batts. Some of those BCC circuits will sense if the house batteries are bad (too low to charge), in which case it will never close that charging relay. My '94 did all that stuff.

You didn't tell us what the voltage measurements of the battery set for the house and chassis are at rest without the engine running...that would be useful info.

PJW73NH · 06-08-2019, 12:10 AM

Thanks to all who took the time to reply.

Here is some more data.

With engine off:
House 12.6 v
Chassis 12.4v

With engine on:
House 12.55v
Chassis 14.2v

See attached pics of the BCC and schematic from "owners manual".

There are three solenoid/relays in the BCC

Top is "ignition", middle is "jump start",bottom is "converter".

With engine running: (X designates a relay secondary terminal per diagram)

12.5v X 12.5v X
14.2v X 12.5v X
12.5v X 12.5v X

I am suspect of the middle (jump start) relay... It appears from the schematic (if I am reading it correctly), that it not only provides the "boost" function, but also the charge function from the chassis batteries (alternator) to the house batteries.

Does this help?

Thank you.

twinboat · 06-08-2019, 02:07 AM

Does the center solenoid get actavated when you push the boost switch or have the engine running ?

If it does, when actavated do the 2 large terminals equal the same voltage. If not it needs replacement.

PJW73NH · 06-08-2019, 08:37 AM

Twin,

Thanks for the help. It's very hard to tell WHICH relay is clicking when I press the jump start switch. All 3 are very close together. It could be either one of them or more than one of them. It sounds like only one of them. But even gripping each one with my fingers it's hard to tell which one is energizing.

I checked the primaries (coil windings) of the 3 relays for voltage.
For reference House voltage AT THE BATTERY is 12.75.

The top one (labeled ignition) on the diagram is a single post. It's got no voltage on it. Whether the jump switch is pressed or not (expected behavior)

The middle one (labeled Jump Start) has (12.3) on both posts when the jump switch is not pressed. It has 11.8v on both posts when the switch IS pressed. (Not expected behavior (per diagram)).

The bottom one (labeled Converter) has (12.3) on the both primary winding posts when the jump switch is NOT pressed. And then the top post drops to 10.7v and the bottom post drops to 1.20v (This bothers me).

I have a couple of observations:

1. Why do I have 12.75v at the house battery and 12.3v at the relays?

2. I suspect the 12.3v drops to 11.8v because the jump switch energizes AT LEAST one relay. So I am not too concerned about this.

3. I AM concerned about the bottom relay primary winding post voltages.

Any thoughts?

Thanks again for all the help.

Jim_HiTek · 06-08-2019, 08:46 AM

You know which winding of the coil goes to the battery (or you should). Take the wire off the other side of the coil and make a jumper wire that goes to ground. Than just tap the coil terminal. That way you can hear whether that coil is operational. You can also remove and insulate one of the large wires...then measure to the unconnected terminal when you ground your jumper wire. Should be withing 0.5 volts of the connected wires voltage when the relay is operated.

You can do all that without the engine running...but be careful to keep loose wires insulated.

Take care of one thing at a time...move to the converter issue after solving the charging issue.

PJW73NH · 06-08-2019, 09:20 AM

Hi Jim,

Regarding my comment about the bottom relay, I guess I was thinking that this may have had something to do with the issue at hand (charging) and I added it for a data point.

We are heading out for our return trip home in about an hour, so I don't think I will doing much more (mechanical) work on this until we are safely home back east. (Though I am happy to continue our discussion if I find new information) I don't want to take the chance of making things worse. We have a small Honda EU2000i as a back up to use as "shore power" to get the converter to charge the house batteries enough to start the big on-board genny if the house batteries get too low.

The coil wires on the relays (at least the ones I can see/follow) do not appear to go directly to the house battery +. It looks like they go to a little PCB mounted in/on the lower right side of the BCC box (take a look at the diagram) that has 3 - 1 ohm 5 watt ceramic resistors. I wonder what their purpose is. Pull-ups?

Thanks again for all the help. When we get home, I'll dig in a little further.

One other question. If it DOES turn out to be the relay, do you think, are there "generic" or alternative manufacturers/suppliers of the relay (see pic) that some electric supply houses might have in stock. IE would ANY 100 amp 12v relay do, or do I need the exact replacement.

Thanks Jim.

Paul.../NH via ID.

Jim_HiTek · 06-08-2019, 09:50 AM

Just before you leave, with the engine running, take your trusty rubber mallet and whack those relays.

Have a great trip!

Jim_HiTek · 06-08-2019, 10:53 AM

The relay you showed the picture of is the wrong one. Don't use it. It's not continuous duty. Use this one: https://www.amazon.com/TERMINAL-CONT...gateway&sr=8-3

You can use this one to sub for a 901 but not the other way round. And to answer your question, you can use ANY 12 Volt, 100 amp, continuous duty relay with 4 connections. Makes no difference what the brand is if you can fit it in the spaced available and it's rated the same. It's just much easier to use the exact replacement. And the price of $37 via Prime and 2 day shipping is easy to take for a relay with those ratings too.

Assuming I got those relay numbers correct. Best to just remove one of yours and see what the label p/n is.

I see those relays all have a connection to the House batteries via that buss. So there's 12 volt on one side of each relay coil. So you could remove the other lead and short that terminal to ground to verify that the relay operates.

The resistors are probably speed resistors for the heater fan.

PJW73NH · 06-10-2019, 01:05 AM

Hi Jim.

Two days out. No cell service. We've been out of contact. Yes, I had already tried the rubber mallet trick. No dice. This is becoming a pain. While driving we use house batteries for GPS, dash-cam and charging 3 cell phones. By the time we land for the evening, the house batts are pretty low. The first night we had enough juice to start the Kohler for a couple hours. We used the house batts that night and ran them out. The next morning, we had to use the Honda to "shore charge" the house batts enough to start the Kohler and make coffee.

Tomorrow (today), I hope to get a 4 ga battery cable that has a post connector on one side, and an "eye" on the other. I'll tie the "eye" side to the chassis side of the relay secondary, and then manually connect the post connector to an available + post on the house batts. I'll connect it in the morning just before we drive off, and disconnect at night when we land and are done driving for the day. Hopefully charging the house batts all day while driving. Essentially acting as a "manual" battery isolator. I'll have to cover/insulate the disconnected post connector overnight so it can't short out to anything.

Thanks for the correct info on the relay. I'll order one and replace when we get home.

Paul.../NH

Jim_HiTek · 06-10-2019, 07:03 AM

I'd recommend a change in your procedure...

Start the engine and charge up the chassis battery. Shut down the engine. Jumper the two battery sets. Restart the engine and drive off. The reason is that you do not want to strain the alternator. You're dead in the water if that blows from the excessive current required by two battery banks.

Some people in this situation use light duty jumper cables when needed. But usually not when driving. Easier to attach and detach.

PJW73NH · 06-10-2019, 07:46 AM

Thanks Jim, That's a good idea. I didn't think of that. We've been on shore power all night, so the house should be all topped off. But as we travel, each morning we'll start the engine and run it for a 10 mins or so before connecting the house batts. Does that sound OK ?

Do you think there is any reason to disconnect either of the primary wires to the relay?

Thanks.

Paul.../NH

PS. For whatever reason, when I am on my hotspot, the forum will NOT let me login. It accepts my username and password and says "thank you PJW73NH for logging in", but just brings me back to a login screen. if I use a public wifi (which I have at least for this AM) it lets me in fine. I mention this just in case you don't hear back from me for a while.