Why solenoid?

[AH_AK]

Why do the majority of RV manufacturers use a latching solenoid for the battery disconnect (storage) as opposed to a mechanical battery disconnect switch?

Is there some other function that the solenoid is performing that an appropriately sized manual SPST switch would not?

There has to be a reason for the added complexity and cost.

[wa8yxm]

I have had to bypass my solenoid.. ONCE.

YOu can install a bypass switch for emergency use. Easy to do.

[pianotuna]

2112 wrote:
PT, I'm surprised you didn't replace the continuous current draw disconnect relay with a latching type. You seem to be very efficiency minded.

Hi 2112,

I had to replace the oem solenoid--the contacts were pitted and burned. While I was at it, added a 2nd charging path, from the battery. This was an attempt to increase "house" battery charging. The replacements I used were rated at 200 amps continuous. I also added manual control for each solenoid. Both circuits are protected by an automatic 50 amp circuit breaker.

Each solenoid draws 0.88 amps.

To be fair, I was not aware of latching relays at the time--or I might have gone that way.

[AH_AK]

I had assumed they were all the magnetic latching solenoids. If I am not mistaken, permanent magnets hold the position open or closed (latching action) as opposed to a seal-in circuit. Any relay requiring continuous holding current would seem like a really bad idea for RV applications.

One of the reasons I am barking up this tree is because occasionally when my batteries get super cold and low on charge they can’t switch the solenoid. This means I can’t charge the batteries either. I can bypass the solenoid in order to charge the battery but this is inconvenient. A switch on a solenoid bypass circuit is probably the best route for solving this occasional issue. Also, I probably need new coach batteries, but that is a different post.

dougrainer wrote:
AS other have mentioned, There are 2 types. LATCHING relay(soelnoid) takes current to engage and disengage, but once either is done it requires NO current to keep closed or open. Yes, this type system is more expensive, which you usually only see it on Motorized due to access to the battery banks. The other requires continuous 12 volts to keep engaged. These types are cheap because all you need is a simple ON/OFF switch. Also these type solenoids also build up heat when you have a load and constant power to them to keep closed.
COST? Well, when you factor in the cost of most Motorized and the fact that RVer's want bells and whistles, they make it standard. Now, the drawbacks to Latching type. Some OEM's do NOT run all Coach 12 volt loads thru the disconnect. Some, wire the CO and LP detectors direct to the batteries for liability reasons. So, with Batteries OFF, they can still be drained in 2 to 4 weeks. Inverter/Chargers are NEVER wired thru a Latching disconnect and are wired direct to the Coach batteries. Doug

[AH_AK]

As I said in my comment above, for my truck camper the distance is not an issue due to the location of the battery compartment. Maybe an extra 3 ft of 8 AWG required to install a switch. At least for me, a switch would likely be cheaper. For a large RV with extra wire runs and a higher rated current, the solenoid makes total sense.

wa8yxm wrote:
The Solenoid, basiclly a big and I mean BIG relay. can easily pass 100 amps or more. The wires that run a great distance to the switch. just a couple amps.
You are asking why they use a fairly low cost remote switch with low cost 20-22 ga wires instead of oh say 50 feet of something between 4ga and 00ga.

Way cheaper. and way better electrically as well. (less voltage loss in the line).

[dougrainer]

AS other have mentioned, There are 2 types. LATCHING relay(soelnoid) takes current to engage and disengage, but once either is done it requires NO current to keep closed or open. Yes, this type system is more expensive, which you usually only see it on Motorized due to access to the battery banks. The other requires continuous 12 volts to keep engaged. These types are cheap because all you need is a simple ON/OFF switch. Also these type solenoids also build up heat when you have a load and constant power to them to keep closed.
COST? Well, when you factor in the cost of most Motorized and the fact that RVer's want bells and whistles, they make it standard. Now, the drawbacks to Latching type. Some OEM's do NOT run all Coach 12 volt loads thru the disconnect. Some, wire the CO and LP detectors direct to the batteries for liability reasons. So, with Batteries OFF, they can still be drained in 2 to 4 weeks. Inverter/Chargers are NEVER wired thru a Latching disconnect and are wired direct to the Coach batteries. Doug

[wa8yxm]

The Solenoid, basiclly a big and I mean BIG relay. can easily pass 100 amps or more. The wires that run a great distance to the switch. just a couple amps.
You are asking why they use a fairly low cost remote switch with low cost 20-22 ga wires instead of oh say 50 feet of something between 4ga and 00ga.

Way cheaper. and way better electrically as well. (less voltage loss in the line).

[2112]

PT, I'm surprised you didn't replace the continuous current draw disconnect relay with a latching type. You seem to be very efficiency minded.

[pianotuna]

The solenoid for mine is not a latching relay. It is a continuous use design.

[AH_AK]

That makes a lot of sense. I have a truck camper and the solenoid and switch are right over the battery compartment/generator. So for me, it’d be easy to use a switch, but for larger RV’s I can see the advantage.
Thanks for the info!

[2112]

And you can install multiple convenience switches throughout the rig. Similar to one pump switch in the kitchen and another in the restroom.

[enblethen]

It is actually a Latching Relay!
As others said it is for ease of installation.

[Bobbo]

LittleBill wrote:
because the switch can be placed in a much better place then a mechanical.

This ^^^^^^^^^^^^.

With a manual disconnect switch, you have to place it between the battery and the electrical panel, making it very inconvenient to access. Using the solenoid lets you place it anywhere, and place its switch right by the door, where it is extremely convenient.

[LittleBill]

because the switch can be placed in a much better place then a mechanical.

[SAR_Tracker]

Convenience for the non-mechanically/electrically inclined. It's like why have an auto-switchover for propane?