Autopilots destroyed by spikes?

I have had 3 Raymarine Type 300 autopilots electronics destroyed in 3 years. With the help of Raymarine I have determined thatit is possible that the electronics are being destroyed by spikes or surges on the 12 volt supply. These spikes/surges may be caused by the bow thruster and windlass being wired to the same battery bank (400ah) as the autopilot, or there may be some other cause - fridge bilge pump etc.

How can I protect the next new (and expensive) autopilot computer from destruction? The autopilot is fused at 40 amps

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Sep 08, 2007
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More Autopilot Solutions
by: Bill

I forgot to fully mention you can Use MOVs (MetalOxide Varistors) instead of a power resistor! just talk to the store rep about getting ones made for Low voltage uses (Or current) I am somewhat rusty in this section as it's been so long since I really had to deal with high current surges.

The best methode by far is having a dedicated instrumentation batery bank that's powered via a good quality cyclic charge controller, that way you are isolated from the main system and the voltages are tightly clamped down providing clean reliable power to the most important items on your boat!

It is always better to spend the extra money on a well designed and implemented system then to save money and find yourself swimming! I personally prefer to have highly modular systems each isolated from each other, far more expensive but I can't really say I've every had a problem with any thing other then the engine! not even a blown fuse!

Basicly with the MOVs we're making a Surge arrester akin to the AC surge bars, Only instead it is DC surges we are arresting, the capacitor will stabilize the current and provide excelant on demand current when it is most needed (when turning it on, or doing an intensive computation) and will arrest any ripple and filter out frequancy pollution, The resistor or MOV how ever will burn off any over currents by resistively shunting them to ground, there by not blowing the fuse yet dumping the over current situation! and since we have a cap in circuit it will stabilize every thing! so the device dosn't see any of the action and only gets a clean healthy supply current!

Sep 08, 2007
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Autopilot Solution
by: Bill

Have you tried a electrolytic capacitor and a resistor in paralel to the DC input?
----- + ---+AutoPilot
| |
| -
x ___ 100uF 50V
| |
---------- -AutoPilot

x = a resister slightly higher then the circuit of the AutoPilot, The capaciter resister combo aut to absorb the insurge and drop surg equaly. only problem is you need to make shure the resister is switched off with the unit, and or can be switched off when running only on bateries, not the worlds most sophisticated method but has worked for me in the past

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