Boost start switch

[Chuck Seidel]

I have a 99 Tripical on a Ford F53 chassie. My start boost switch does not energize the solenoid that connects the two batteries together. Their is a relay on the 12volt distribution panel that I think should be closing when I depress the boost switch and then closing the solenoid. If anyone knows how this system works or has a wireing diagram of this system I could sure use some help.

Thanks Chuck

[Chuck Seidel]

I have a 99 Tripical on a Ford F53 chassie. My start boost switch does not energize the solenoid that connects the two batteries together. Their is a relay on the 12volt distribution panel that I think should be closing when I depress the boost switch and then closing the solenoid. If anyone knows how this system works or has a wireing diagram of this system I could sure use some help.

Thanks Chuck

[Richard S.]

Chuck
You may want to disconect all power and your battries and check and clean the wires and cables on the solenoid and the battries.

[Mike Canter]

If that is like mt Dolphin that Battery Boost rocker switch sends 12 volts directly to a Ford type starter solenoid that is located in the battery compartment. To energize this solenoid requires very little power so I doubt that there is a second relay in the circuit. Also if the batteries ran down you may not be able to energize a second relay. I would do as previously posted on cleaning the connections and making sure they are tight. Have a partner hit that switch a couple of times with your head in the battery compartment and see if you can hear it clicking. If all else fails go to your NAPA parts store and buy a part number ST-85 solenoid (maybe ST-80) and replace it.

[Capt. Flipper]

Chuck,
The circuit to energize the boost function is more complex on a National coach than you might imagine. Yes, pressing the button applies 12V to solenoid circuit... no relay involved. But, the solenoid is activated by other conditions as well. If you are connected to shore power, gen is running or the engine is running, the solenoid will probably already be engaged. Simply placing your hand on it will tell you if it is. It will be warm. There is a circuit that monitors chassis vs coach battery voltage and turns off the solenoid if either drops by a preset amount. This prevents running down both batteries. If the cahssis battery is below the preset, pressing the boost switch will connect the coach batteries to assist in starting. That is about the only condition where you can be sure to hear a click with button press.

Having said all that, the most common failure is oxidizing of the contacts in the solenoid. The easiest thing is just replace it. If you are qualified electrically, measure the voltage across the 2 large posts on the solenoid. If it is zero, the solenoid is engaged and probably OK. If it is more than .1V, and solenoid is warm, it is bad.

Hope that helps

[DarrylGF]

RV Custom Products in Santa Fe Springs makes the 12v distribution board. Their # is
562-921-8353. You may not get the gentleman as he is busy but leave your # and he will call you back. You can order the relay by itself and install it if that is the problem. The whole board cost right around $300. A RV repair shop told me it would cost $425.00 but didn't say how much it would cost to install. Just take a photo of the board so you know where all the wires go back. RV Custom Products has drawings also to help you trace the wiring.
DarrylGF
99 Nat Tradewinds 7370

[DarrylGF]

Oh by the way, I see Mike Canter said the relay is like a Ford starter relay. I was informed by RV Custom Products this relay is a continuous duty relay and the Ford starter relay is intermitten duty. If you try to replace the relay with a car starter relay it will burn up in a short time.
DarrylGF
99 National Tradewinds 7370
No Toad yet

[TropiCal-Tex]

Chuck, I also have a 99 Tropical on the F53 frame. Last only time my boost switch has failed to work for me was when I lost a cell in one of my coach batteries. The voltage was too low, so the solenoid didn't even click.

I was able to start the generator (barely) and then the converter put enough juice into the system to allow the Boost switch to work, and start the engine.

So bad batteries or dirty battery connections are where I would start.

[garym114]

In parts terms it is an isolator relay. They typically come in 100 and 200 amp varities.
The 100 amp continuous duty relay you need is Intellitec part number 77-90000-100, $38. http://www.slesolar.com/items/item2055.htm
On my 2000 Sea Breezei t closes when either chassis batteries or coach batteries get above 13.2 volts (chassis charging or engine running). Can't remember the opening voltage but it does open when either battery starts to discharge to prevent the other from discharging. And, the boost switch will close it.

[Flagelpater]

Just wondering! Is the power for the relay coming from the chassis battery or the house battery? I would expect it to be coming from the house battery. That is normally the system that is going to do the helping. As stated above, the relay worked after the GenSet was fired up, makes me think the relay power is coming from the dead battery system! Also, I have experience using this type system in aircraft, and after selecting the Boost Relay ON, we were instructed to hold it closed for 1 minute to help the batteries stabilize a bit before engaging the starter, FWIW. Flagelpater

[garym114]

The power for the relay comes from the circuit on the 12v board which is connected to both batteries. The voltage going to the relay is not equal to the voltage of either battery set. It makes no difference in the voltage if you have just one battery set hooked up. The voltage is still there to operate it. I had mine out to try to see how it operated.