Jim you said "What I did was hold the rocker switch on just until I heard it the big relay click, then turned on the ignition (but not try to start) I could then release the switch and the contactor remained latched in until I turned off the ignition.". Jim and Mike H Can you check this? If you just get in the coach and turn the ignition key until the idot lights light up in the dash cluster, and check and see if the relay is closed. I did it just a second ago by having my wife turn the ignition switch while I just held my hand on the relay. I believe you are going to find that the relay closes. i don't believe there is any latching relay in the circuit, its possible PC changed something but don't see why they would add it to the wiring when its not needed.
Jim I believe this relay closes to charge the house batteries while traveling. Some older RV's were not wired this way and the only way to get the batteries charged was either solar or to plug in/generator and use the converter. Instead of using the white switch on the dash you could simply turn the ignition switch to the position where the idot lights light and do the same thing as the switch. The only down side is that you power up items like the ECM and other electrical components that are just using power which is defeating what you are trying to accomplish ( raising the chassis battery voltage using the house batteries). It looks like the wire size is about a 6AWG going to the relay on the load side. This tells me that it isn't sufficient enough to carry much of a load from the starter, thats why there is a automatic reseting circuit breaker on the load side of the relay from the house batteries. If your chassis battery is weak, you will most benefit by holding the rocker switch to close the relay and wait. You need to give it some time for the house batteries to discharge and bring up the voltage of the chassis battery ( batteries are actually trying to equalize voltage between them). That is why some people on here have installed a toggle switch, so they can simply flip the switch give it 5 minutes or so then start the engine. It should be noted that this wiring scheme only will work if the battery is low on charge, if the battery is sulfated and shorted across the plates it won't help, it will just start draining your house batteries.
OK, Lance. Since I was already working on a post to another message in this string when your above message hit---I'll just add a couple of comments to your thoughts. To preface, I'm
not the expert on this issue. Several years training and work as an electronics technician (many, many years ago), give me a pretty good understanding of these type systems, but my comments are opinions only.
First, you're correct, the primary purpose of this relay is to provide a way to connect/disconnect the house batteries to the Ford 12-volt system to allow the alternator to charge them. Older systems used isolator diode units to do this, but everything later transitioned to relays. You're also correct that this is not a "latching" relay. It is simply activated by the key switch--it's open (disconnecting the house batteries from the Ford circuit) when the key switch is off, and engages (connecting the house batteries to the Ford 12-volt system) when the switch is turned on
What Phoenix did with the "white switch" (as I mentioned in an earlier post), is just provide a second way to engage the relay from the house batteries. If the chassis battery is fairly dead, there won't be enough voltage to pull in the relay by turning on the key switch. But you can activate the "white switch and feed 12 volts from the house batteries through that switch to the relay coil to pull in the relay, connecting the house and chassis batteries. This effectively allows the house battery charging circuit to be used in reverse to flow current from hot house batteries into a dead (or low) Ford chassis battery.
You're right that you can't provide "cranking current" through it--the 40-amp circuit breaker in the relay circuit limits current to that amount--and you also can't overcome a chassis battery that is shorted or open internally, but a good hot house battery bank can provide a pretty good boost to the Ford system over a period of time. Info in the (very limited) Phoenix Owner's Manual that I received in my package recommends activating the "white switch" and then waiting "about an hour" before cranking the Ford. That amount of time would pretty much allow a dead but decent chassis battery to fully equalize with the house batteries--likely enough to start the Ford.
Lastly---the question of whether to hold in the (momentary) white switch, or exactly how to do it. If the chassis battery is not too low (say barely cranking, but not enough to start), one might hold in the momentary switch for a while and get enough help in there from the house batteries to allow it to crank off. However to follow Phoenix's suggestion to allow an hour---well, that's a long time to hold in a momentary switch. For a really dead battery, probably the best bet with the momentary switch would be to hold it in long enough to let the house batteries get the chassis system voltage up to the point that the relay will hold in from the key switch feed--then just the key switch being on will keep the relay in. You're right that that approach means that the other systems that come on with the key pull some of the power you're putting in from the house batteries, but probably won't pull enough to defeat the process. That's where the option of the toggle-type switch recommended by John (Keelhauler) comes in. The toggle switch eliminates having to hold in the momentary switch (and/or) then use the key switch for long periods. The only concern that may come with that method is the possibility of the switch being left on or turned on when it shouldn't be--with any negatives that accrue from that.
Sorry that the "couple of comments" got more long-winded than intended (and some are repetitious), but as Jim said there's no charge for them.
Mike
