Battery Boost Relay

Joe & Bonnie · 09-30-2010, 07:38 PM

Anyone notice this on their coach? When I'm plugged into shore power, the battery boost relay is energized somehow and that sucker gets HOT! enough to burn my hand.

How and why is that thing continously energized? I looked at Monaco's wiring diagrams and the only feed to that relay besides +12VDC is a switched ground from the batt boost switch on the dash. Two days later that think is still energized.

I once had an Ultra Trikl Start charger wired in but removed it when I noticed the boost relay on all the time. I think I've read some discussions before on this indicating that a BIRD (?) isolator/relay/whatever up in the front run compartment is involved.

I'm stumped. This doesn't seem normal. Can anyone clue me in on this?

bullydogs1 · 09-30-2010, 07:54 PM

That relay is what charges your chassis batteries when plugged into shore power and what charges your house batteries with the engine running...That mega tech board in the front compartment sends a signal for the solenoid to close. This happens when your batteries are at 13.2 volts and your other side is at 12.1 volts, the solenoid closes and the entire bank of batteries is supposed to charge until 12.2 v...You can call mega tech of oregon and they will tell you about it...There was an updated board used which may have some better software in it..It keeps the banks with usable batteries..although not at full charge.

Joe & Bonnie · 10-01-2010, 07:22 AM

Bullydogs1:
Thanks for the feedback. However, in looking at the wiring schematics I got (and had to pay for!) from Monaco, all I see is a switched ground from the boost switch. I opened the front compartment and I see the Mega Tech board but I don't see a connection to the relay in the battery compartment. So.. I'm still asking How does that relay get (and stay) energized?
If anyone has additional wiring diagrams for this area of interest, I would greatly appreciate a look at them.

Robi.1014 · 10-01-2010, 08:02 AM

In a plain-vanilla RV system the battery-boost relay is energized by applying full battery voltage across the BB-relay (in your case: switching one of its leads to ground) . Typically these BB-relays are like starter-solenoid relays: they are not designed to be continuously energized. Yours seems to be continuously energized (hence getting VERY hot), so it's time to find out how and why a "continuous ground" is occurring.

And some basics:
Once a 12v solenoid has been energized, keeping it energized (if that's what you want to do) requires substantially less voltage. So a more sophisticated approach is to apply the necessary 12VDC to energize the relay, then to electronically lower the DC voltage so that the relay energizing coil does not get hot (but stays energized). This approach not only uses less amperage, but it affords engineers the ability to make a non-continuous-duty solenoid into a continuous-duty solenoid. Ta Da.

But your Monaco documentation (similar to mine) shows no sign of this "sophistication" I mention above. But what I have observed is that even if I manually/continuously hold down the BB-relay-switch (at the dash), the relay will NOT stay continuously energized. I haven't bothered to look into this any further, but there must be some "electronics" in my circuit to override the simple push-to-energize BB dash switch.

So back at ya:
Find out where your "continuous, full-voltage ground" is coming from ... and I think you'll solve your problem....before it catches fire would be nice.

Diplomat Don · 10-01-2010, 12:00 PM

Joe and Bonnie......I have very little expertise in trouble shooting electrical systems and I may be full of baloney, but I think a simple test to see what is going on is to disconnect the Mega Tech board in the front bay and see if the relay still gets hot.

My coach didn't come with the Mega Tech board so I originally used a Trik-L-Start to charge my house batteries. It eventually went bad after about four years. I bought the Mega Tech board and a better quality solenoid (the one you're having issues with) because there were complaints that once you installed the Mega Tech board it ate up the older solenoids.

Once the system was installed, I felt unconfortable with the way it worked and how it was charging my batteries......issues like you're experiencing. I removed the Mega Tech board and went to a Xantrex Echo Charger to keep my house batteries up.

Again.....my electrical abillities are almost non-existent compared to others on this board, but I think "bullydogs1" gave you good info and the test would be to disconnect the Mega Tech board.

bullydogs1 · 10-01-2010, 04:39 PM

As a follow-up to this, I don't like the way the mega-tech board works right now...the positives go into it and there is a plug there..that plug is what tells the solenoid to close. Take the mega-tech plug out (you don't even have to remove the board ) and I bet the solenoid will stop closing.
Mega-Tech is supposed to come out with an updated software new board by sometime in December...I have spoken to Patti and someone else there about this....and I intend to swap my board for it when it is available. The people there are a pleasure to talk to and deal with.

Joe & Bonnie · 10-03-2010, 08:00 PM

Thank Ya, Stuart! I will follow up on this.

DonGott · 10-12-2010, 07:17 PM

Diplomat Don....... which solenoid did you turn too. My solenoids in the front compartment are hot to the touch also and I was wondering about an upgrade for them. Thanks.........