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VW dual battery use survey

Hello,

The theme here is the use of dual batteries in the VWs. I assume the bulk of responders will have a bus with two batteries.

If you do have two batteries, do you have a switch to enable the second (appliance) battery to be charged by the motor?

If you do have a switch, is it manual?

If you do have a switch, is it automatic?

If automatic is a diode pair used to "steer" the current?

If automatic is a relay used?

If a relay is used, is it energized by the key power? or another point of control?

If you don't have any switch, would you be interested in an easy to install, automatic electronic controlled, relay switch?

How much is the function of automatic battery control switch worth to you?

___________________________________________________________________

Thanks for your participation!

I have a dual battery in a bus. The PO had used an undersized relay and energized it from the key switch. This un switches the (second) battery from the main whenever the key power is turn off.

However, when you key up, and begin to start the second battery wilbe switched in, a bit early for my liking as the starter 100 amps will proportionately flow! a delayed start or something smarter is needed.

The diode switch insures that your second battery is not use during a start and only receives power to charge from the motor. However it does this at a voltage loss of about 1 volt. So power is wasted.

Proposed in an electronically switched relay, the electronics will monitor the points, and when the engine reaches idle speed > 500 rpm then it energizes a healthy switch. This may be the best solution amongst them all!

Marco

Reply to
Marc H.Popek
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I had installed dual battery starter booster relays in some of the kit cars in the past. The relay would allow 24 volts to the starter only to provide enough power to crank over Corvair engines in VW kit cars. Then the relay would revert back to 12 volts when the vehicle was running or off. I will assume that this is not the information that you truly wanted! But it is about dual battery usage! ;-)

later, dave Reminder........ Before you criticize someone, you should walk a mile in their shoes. That way, when you criticize them, you are a mile away from them, and you have their shoes. Frieda Norris

Reply to
dave

The stock (Westfalia) system uses a pair of relays since the voltage drop across a diode prevents the second battery from reaching full charge.

The pilot relay is picked or selected by the output of the dynamo, typically by being wired in parallel with the charge warning lamp. This ensures the main relay will not be latched to the 12v buss until the engine has started and the dynamo is charging.

A thermal fuse is installed in the secondary buss to prevent the sudden discharge of the main battery when a depleated auxillary battery is latched to the main 12v buss. The thermal fuse, which opens and closes automatically, also serves to protect the dynamo, since charging a high-capacity auxiliary battery will usually exceed the service rating of an automotive dynamo (ie, typically rated at 25% or less [that is, the maximum output of the dynamo can only be drawn for one minute out of four without exceeding the normal operating temperature]).

The components for such a system are commonly available for ten dollars or less from numerous sources.

The dual relay circuit is the preferred arrangement and is found on cars, boats and airplanes fitted with auxiliary batteries. Owners of VW buses who have converted them to campers have used this arrangement for years. It is also commonly used by ham radio operators who have installed mobile shortwave transmitters in their bugs & buses. You can find more information on dual battery installations by searching the archives of the various bus-specific newsgroups & mailing lists

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-Bob Hoover

-(KA6HZF)

Reply to
Veeduber

Excellent insight and you are right I did not anticipate this application. For the inverter , converting DC battery to 120 vac for appliances there is significant advantage by using the 24 volt "stand-up" relay in a base 12 volt battery system... Higher voltage lower current for the same delivered power..

Thanks

Reply to
Marc H.Popek

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