Hydraulic reversing pump popping fuses

[howardclark]

Got a Kobelt reversing pump. I think I may have had a problem for several years but not used the autopilot enough to see it.
System requires a 30amp fuse. That will blow quite quickly. A 40 amp fuse will last 30mins or so which is normally all I need .
I looked at the supply with a clamp on ammeter and could see the general current was low but with an occasional spike- presumably as the relays open and close.
decided to go further and put in a 50amp fuse! Was OK for 4 hours in a flat sea then blew! slow blow fuses seem to make no difference.
Think its time I sorted this- don’t really want to change the pump which involves a lot of extra work. Do the electrical/electronic experts on the forum think I am just lacking spike suppression or is this more serious? can I add a suppression circuit ? How can I analyse the problem further?

 

[William_H]

Fuses are often available in "Slow Blow" version. You do not say what style of fuse you have but slow blow I have seen are in the glass tube type. Not seen them in spade type.
Other wise suggest you dismantle the pump motor and check bearings etc. Also check pump for any unusual friction. ol'will

 

[roaringgirl]

I was going to suggest that you measure current under load, but you already know that it exceeds 50A, which seems a lot - is your cabling specced for that?

I don't know what your autopilot is trying to steer, but my ancient raymarine linear motor steers our 12T ketch in any conditions, never going over 20A (@12V), so 50A seems like a great deal. What is the spec of the motor with regard to current, surely it's not 50A?

If there's a bad connection somewhere, it might be driving up the current that the motor draws? I don't think it's safe to keep upping the fuse rating - better to find the problem...

 

[howardclark]

wiring is heavy duty enough- think as a first step I will rewire and take top off relay box to see if I can see any arcing

 

[pyrojames]

If your wiring is underspec, then that won't blow the fuse. The resistance in the circuit will be higher and currents lower. I suspect that the motor has failed or failing bearings, or you rams are overly stiff. Putting in bigger fuses is just likely to cause a fire. That's why it was speced with a 30 Amp fuse in the first place, to protect itself if there is a mechanical fault..