Constant Duty Battery Solenoid Reference

[DaveVA78Chieftain]

Sent: 4/25/2006

Here is a reference to the Constant Duty Solenoid used to connect the chassis and house batteries together.  3 terminal is for a grounded mounting (used by almost all of the 70's era Winnies).  4 terminal is for mounting on wood or fiberglass.  There is a link on the page to a wiring diagram for each type.  This is the relay activated by the MOM switch.  For late 70's model winnies, you may also find one of these relays used for the dash heater.  The wire from the Dodge fuse box heater terminal is feed to the coil terminal of this type of relay.   These relays typically run less than 20$ at an RV store.


There are 3 terminal (shown) and 4 terminal Constant Duty Solenoids.  Winnebago typically used the 3 terminal version.  You have to search the net for a battery Isolator when searching for a new solenoid.
3 terminal types use the mounting brackets as the return path for the relay coil.
4 terminal types have both a positive and negative post for the relay coil.  Allows mounting to a wood or plastic surface.
You cannot use a starter relay like used on older model Fords.  The relay coils are not built to have constant current flowing through them.  You have to have a solenoid designed to be constantly energized.

Sources:
http://www.tomraperrvparts.com/parts/home.php?cat=207
http://www.tweetys.com/search.aspx?find=isolator

Be advised that this can be a very complex issue with several alternatives.

Constant Duty Solenoid (original classic Winnebago installation):  Used with MOM switch.
NORM - Batteries separated (no voltage to solinoid relay coil).
DUAL - Connects both batteries (chassis start/house) together when ignition key is in ON position.  Used to charge house battery with engine alternator
MOM (spring return) - Allows voltage/current from house battery to be used to start the engine.

Isolator Solenoid - smart isolator that only connects batteries together once alternator has charged start battery to 13.5 volts.  Because engine starting drops voltage below 13.5, this relay type does not support the MOM position.

Electronic Isolator (basic versions) - Allows battery charging (no MOM switch support).  Unfortunately, the voltage drop across the diodes typically do not allow a full charge to be applied to the house battery.

Smart battery isolators/regulators - Computer controlled.  Not unusual to be a 3 stage charge version using the alternator.  No MOM swtich support.

There is a world of options out there.
Here is a typical hookup for a constant duty solenoid version on a Winnebago with a Dodge chassis.  The solenoid is at the bottom right of the drawing.


Dave

[GulfCoastFighter0]

Great information, thanks!

[Froggy1936]

Another place for these relays and a lot of stuff  jamestowndistributors.com  relays priced from $26.00 to $60.00  Frank

[George-47]

Thanks for this information...It helps me greatly to not only read the description but to also see the wiring diagram...That was the best drawing I've seen in a while...very good..
George

[DaveVA78Chieftain]

George,
In principle the diagram is good however it is based on a 70's era Dodge motorhome chassis setup.
Your 80's era GM P30 with a 454 will be somewhat different for ignition, starting and charging circuitry.

Dave

[khantroll]

Would it be worthwhile to upgrade to one of the new isolators? If so, is this an example of the smart variety: http://tweetys.com/blue-sea-7611-batterylink-automatic-charging-relay---12v-24v-dc-120a.aspx ?

[DaveVA78Chieftain]

The Intellitec 00-01000-000 Bi-Directional Isolator Relay Delay ( BIRD ) GAS controller has been available for a very long time. 



It controls a standard 100 amp constant duty relay. Bi-directional means the alternator is automatically used to charge the engine and house batteries and the converter is used to automatically charge the engine and house batteries.

Manual


Ultimate DC system with all sorts of goodies: 

[Mikey3air]

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