All these electrical posts have stirred me to ask you guys about something I've been ignoring. The White Rodgers (P/N 586-105111-3) Battery disconnect relay has failed (open circuit-no power) twice in my coach within 2 years. I almost never utilized the option to disconnect the batteries using the convenient shutoff switch by the door but instead would plug the coach in to 110A while parked next to my house. When I finally did use the disconnect, the relay failed and left the circuit in an "OPEN" status. I also should mention this relay always seemed abnormally HOT to the touch. After this relay failed a second time, I removed the relay from the circuit completely and wired the two heavy 12V battery to house cables directly together..I've been planning to find the suitable replacement but I've been procrastinating....This link is for the White Rodgers product that keeps failing. I currently have (2) 6V house batteries ..Waaatayathink?

http://www.white-rodgers.com/pdfs/catalog/cat_page_130.pdf#search='white%20rogers'


http://www.intellitec.com/pdfs/BATTERY_web/5300507.000.pdf

A latching relay is always the better option for this application - however, it'll require a new switch (single pole, double throw) and - maybe - a bit of rewiring.

A normal relay (like the White-Rogers to which you linked) requires constant current to keep it in one position, and none in the other. A latching relay requires only momentary current to change its position; once changed, there's no power required.

I'm surprised that your coach came with a normal relay - I suspect someone changed it along the way.

There are two types of constant duty relays. You have a latching relay and a powered relay

The differences are the power draw when being used. Follow me on this.

The latching relay get a brief shot of power and draws down the solenoid - after it gets down it latches and holds allowing current to pass thru. To release this latch you send power to the other side of the relay. This would be done with a (liftgate switch) momentary on - off - momentary on switch. This type of relay draws no power after you switch it on or off

I suspect that the reason you feel it hot is that your momentary switch was replaced with a regular toggle switch that stays on all of the time.

When the relay goes to the other side and bridges the batteries it is done and no more power should go to that relay. The reason the relay is hot is the coil is still trying to pull the plunger down. Latching relay needs is a momentary switch.

If you throw the switch and the relay latches and power goes thru you're done. Sending power to hold a coil down is wasted and is just burning out the magnetic coil. That is why it is still hot.

The owner of the coach before you could have changed the latching relay over to a regular constant duty relay - he could have changed out the switch. Maybe both. Without looking I'm going to guess that the switch is always on when you throw it. You could keep that switch (not recommended) but remember that after you throw it place it back into the center so there is no more power going to the solenoid.

If it doesn't have it already, install the latching relay. If you want to draw out what it looks like and send it to me I'll try to draw up something for you to replace it with. This should really be a straight out latching relay swap and an understanding not to leave the switch with power going to it. After it latches or unlatches it's done, no more power is needed, no more hot to the touch relay.

hummm,

Rusty, you only beat me cause I was typing a long response! I want a recount!

Got to go to work ABF has a broken down truck - time to make the "dough" nuts

I think it was only because I'm sitting here at 70 F and your trying to type with numb fingers...

Rusty stated that it is a single pole double throw.

I think it's a double pole double throw.

Either way the switch is still:
Momentary on - off - momentary on

It could be either but while heading out on that ABF call a thought hit me.

If the latching relay needed power to draw down both sides (or release the latch) then it must need ground to both sides.

It's a little like a window motor in your car. Operate the switch one way and the window goes down - the other way and up it goes. They do this thru a special switch that just reverses the ground and hot.

In this crude example I drew out how this would work. After you hit the switch one way the hot and ground goes to each side. Hit the switch the other way and it reverses the electrical current. This explains how the latching relay knows which way to go.

If the current goes to one side hot then the coil would draw down the plunger. Reverse the hot and ground and the coil goes in the other direction. It makes a lot of sense from a manufacturing standpoint: why put in two coils when you could get one to do the same by reversing the polarity.

You can make a regular 6 terminal momentary switch do this by running jumper wires across the center from each outer post like in the picture. X pattern.

This is the same way a car window knows if it should go up or down. Reverse polarity.



Which way it's wired in depends on the "latching solenoid". I think the last owner didn't have a clue with the electrical and instead of finding out he ran it like a regular relay would. This would explain just about everything you posted.

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Addition to post editing

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Latching relay/solenoid



they come in a normally open, normally closed, single latching or a double latching configuration.

Would need to know how yours is wired in, it would help with the actual solenoid/relay for your application.

These relays/solenoids are also found in a lighter duty setup for other applications like solar power chargers.

A normally open relay allows no power/current to cross the heavier main terminals without activation. It is "open"

A normally closed relay would allow power/current to cross the heavier main terminals without activation. It is "closed"

Which way is up to the application but because it is a latching design it is not that critical.

Now if it requires a regular style switch like Rusty's post (it could be, depends on relay/solenoid) then it is wired in like this

I should have been more specific - Bill's details on the switch are correct.

In any event, a NO or NC relay isn't the correct type - a double latching relay is what's called for, regardless of what's in there now. The relay installed isn't designed for continuous duty, and that's why it failed - but it shouldn't have been there...

Wow, thanks you guys for your help. I have done some troubleshooting in the past and I think the switch at the doorway (wired to relay) is an on-off SPST switch. I'm not positive but I think that Rusty described my circuit when he said I have "continuous power" to the relay causing it to get hot and fail. I'll go home at lunch and give another report this afternoon..

Some latching relays are designed to disengage even if the switch is not momentary (the coil is disconnected when the relay's throw is complete).

In that case, you'll have a single pole, double throw (SPDT), but it will operate mechanically no differently than a single pole, single throw (SPST) - an on-off switch.

To determine, remove the switch and see how many connectors are on the back. A SPDT will have three, like Bill N Y's diagram, but can be used as a simple on-off switch by not using one connection. A SPST will have two.

If you have a SPDT, then most likely, the wiring is there, and only the relay needs replacing with the correct type, although you're going to get to play Electron Detective to trace those wires....

We are both on the right track. Electro detective work would tell a lot more than trying to guess at all of the different configurations that could be wired into something like this.

That's why I like the "big switch." I think it works better and people can wrap their head around the diagnosing without having their eyes glaze over. Less problems with more benefits.

Imagine this: No isolator - no double latching solenoids - no SPST DPDT SPDT blah blah blah.

We've been discussing the major electrical challenges on the modern motorhome. If there was no isolator and no disconnect latching solenoid anyone would be able to trace out the starting/charging/battery draining problems. Very simple to set up and diagnose.


This was discussed at greater length on this post.

Totally agree on the battery switch. If there is room, a Green Knob disconnect on each bank is even simpler. I use them for isolation, paralleling, bank management, etc. Good for anti theft, too, if the knob is somewhere else. Good for shutting off toad batteries, too, both for anti theft and drain reasons.

Disclaimer: I have no financial interest in the Green Knob company.

Well gentleman this is what I found tonight. The remote switch at the entry way is a SPST switch. One terminal of the switch is HOT-12VDC. The other side goes to one of two small posts on the relay in the rear engine compartment. When the SPST switch is in the "ON" position, I measure 12vdc at that same post on the relay in the rear engine compartment. The other small post on the relay goes to ground... I tested this by isolating this wire and tested continuity to the engine block. SOooooo, whaattayou think? I've had the battery cutoff knob style in my previous coach but really don't want to start running heavy battery cables and drilling holes in the Barth.

I suspect the 100A here is enough (you don't need the pair as shown in the brochure) - it won't break the bank at $53. or here at <$40

It's also rated at 500 A for 30 seconds, plenty of margin for an emergency start (although the emergency start should connect directly to the house batteries, by passing the relay! That's normally disconnected, so there's no drain).

You would be best also getting the Intellitec switch and wires, as I don't know how finickey they are on warranty. Their switch should fit into your bezel (which from the 200A relay is DPDT momentary)- You will have to run a pair of (or 3) wires, but you already have the existing wire to use as a messenger. Besides, one of the joys of owning a motorhome is grubbing around underneath it...

The heart of the system is a unique latching relay developed specifically for this purpose. While this relay is capable of carrying heavy coach currents, it requires NO power to stay open or closed. It only draws power during activation. The relay is sealed against the environments and designed to withstand the shock and vibration experienced in the most severe RV or boat applications.

The Battery Disconnect Relay is a mechanically latching switch that operates by the momentary application of battery voltage to the coil terminals in one direction for latching (closed) or the other direction for unlatching (open).

The way I read this is you would need to use the top diagram with the 6 terminals to run the wires for this style latching relay.

It states that voltage is applied one way to latch and another way to disengage. The DPDT (momentary on - off - momentary on) would be the only way to operate this. There is no need for any type of a control panel just the correct switch and the relay.

Intellitec Battery Disconnect Relay
Cat No: MT01-00055-000 $53.00

The only difference between the latching relay pictured (MT01-00055-002) above and the one that you linked to MT01-00055-000 is an extra fuse.

It also looks like it is a single latching relay and not a double latch, I can't be to sure but the description only indicates one latch and return spring. This relay is a normally open latching relay that requires reversing polarity to engage and disengage.

quote:

Originally posted by hilarlee:
The remote switch at the entry way is a SPST switch.

Is this a toggle or rocker style switch? Do you have a control panel or is it just a switch.

Somewhere, someone on the web, said that the switch reverses polarity to throw the relay the opposite direction; I'm skeptical about that claim, but if it's true, then you're absolutely right, it's a single.

But I think it's a double, and my welding machine is bigger than yours...