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**Bernd Felsche[_2_]** · October 29th 17, 02:36 AM posted to rec.autos.makers.vw.watercooled

wrote:

>I want to modify the circuit to add another relay to power the
>solenoid thus lessen the load, to energize relay it takes around
>150mA.

>Supply taken directly from battery.

Solenoid current draw is around 30A. The starter solenoid performs
two tasks; to switch the very much larger starter motor current
(300+ amps) AND to engage the starter motor's drive pinion.

A solid state relay (SSR) will switch faster than a mechanical relay
but is more expensive, especially when allowing for engine
compartment temperatures. When shopping for one, make sure it's a DC
SSR and rated for at least 105 degrees C operating temperature. You
can tuck it in near the battery so that it's not exposed to the
hottest parts of the engine.

If you're good with electronics, you have the option of making your
own solid-state relay around a high-side MOSFET with "logic level"
control. There are lots of them made by e.g. Infineon designed for
engine-compartment (automotive 125 degrees C) temperatures. They can
switch up to hundreds of amps, depending on type.
--
/"\ Bernd Felsche - Somewhere in Western Australia
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