My experience of this group is that there's usually someone who can give an answer to really any query.
I'm too not sure if I'll get that service with this one, but I'm sure some sort of help will be available, even if a re-direction to somewhere else on the net.
I've been asked to repair an early 1980's yacht autopilot. I haven't seen the kit yet but at the moment I'm adding the owner's report to the informat ion I'm finding via Mr Google and consider it likely that the relays that d rive the operating motor have burnt out their contacts. Apparantly the rela ys click but nothing else happens. Relays and inductive current at 12v dc d on't really go together.
As I said I haven't seen the kit so this is my starting point. If the long
-range diagnosis is correct, I am wondering if there's an electronic replac ement for the relays. I've no idea at the moment what the motor current is - maybe half a dozen amps ?
I would agree wwth your long distance diagnosis. The relays will be constantly cycling, so will wear out quite rapidly I would imagine. SCR's would be the modern way to switch DC on and off.
If you can get to the contacts, shoving a female* nail emery board between works wonders. Did that on my XJS once.
yers. or the motor has cone short and fsked them. Or the wires to the motor are OC. Start by isolating the motor to see if it runs. I'd guess te relays are reversing it in an H bridge.
You can build an H bridge pref. with popower FETS.
BUT what you want is a model car reversing controller... they handle up to 30A + at 12v - maybe more. All the power fets are there, and the drive circuitry. You can even make it throttle :-)
The challenge is to go from whatever drives the relays to the 5v 0.5 -
1.5ms pulse you need to drive the car controller. PRF around 20Hz is pretty standard on a model radio setup
controller will have a 5v regulator on board
Ah. this looks even better. Dimension engineering are the bees bloody knees
25A (50A peak) up to 24V reversing motor controller with various operational modes.
designed for robots. And what is a yacht but a frigging great robot?
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if you cant pick up the relay coil signals and adapt to one of its analogue modes, you aint a DIYer.
You might need to replace patch in a simple bit of something to do the voltage level/logic adaptation.
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It all depends on how the autopilot actually works. If its actually taking its input from a pot then you can ditch the guts totally and hook this lot up to the pot.
If its a gyro..well you can buy model helicopter piezo gyros that will hook direct in and keep to a constant heading. All you keep is the case and the motor.
What we need to know is what the motor is and get a rough idea of the total guts and where the signal comes from.
Top whack cost £100+ labour id say. Given a case and the mechanicals and motor.
If you need 12v brushed motors of serious quality i've got a few spare Astro cobalts and the odd Mabuchi and Sagami ferrite, surplus.
If the relays have lasted 30 years but are now the problem, I'd just replace them with the same (decent quality) ones. Electronic relays ain't 100% reliable.
Nothing much more inductive and high current at 12v than a car starter motor - yet the contacts for that seem to survive ok.
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