Voltage but no current

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roaringgirl

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I'm pretty sure my AGM house bank is nearly dead. It has been showing some very low voltages recently despite getting plenty of charge. However, after 24 hrs of motoring (and therefore charging) plus a couple of sunny windy days, it now shows as fully charged (12.9V at rest - judged by the BMV).

Is it possible that although it is sitting at 12.9V it still lacks the current to spin the anchor windlass? I'm seeing some very strange behaviour, and have just confirmed that the windlass motor is good by rigging it up on a friend's boat...
 
Yes quite possible the battery can show decent voltage but completely fail in supplying power. However you would usually get a bit of a grunt or attempt at moving the winch before it dies completely. The effect you have is perhaps more likely coming from a really poor connection in the circuit. If you can put a volt meter (multimeter) across the battery it self (actual terminals) and check when you try to operate the winch if the battery voltage there does dive down you have a dud battery. if the battery voltage holds up you have a bad connection. Start with the actual battery terminals then any switches or fuses in circuit then check actual wire. Do this by moving your volt meter down stream to see how far volts get under load. I have had a failure of wire itself where it some how got the insulation punctured and corrosion got in to destroy the conductor but the corrosion would carry enough current op operate a volt meter. good luck ol;'will
 
I tried removing wiring from the equation by doing it at the battery and got the same result, so although it seemed like wiring, I don't think it is.

When I tried it just now, the solenoid clicked once when I pressed the button, but then wouldn't click again on subsequent attempts. The same happened with my tests with the solenoid at the battery itself, even though there wasn't much discernible voltage drop under load.
 
Seems like time for a battery replacement.

If interested, battery load testers are not too expensive and will immediately show how batteries hold up when working.

I'm using this type. No digitals, no internal battery. Rugged and simple:
54c8893bce290_-_battery-testing-0907-de.jpg
 
I have seen similar and it sounds like you need a new battery. What happens to the battery voltage when you apply an electrical load?
The only other possibility is battery isolator switch faulty.
 
MartynG said:
I have seen similar and it sounds like you need a new battery. What happens to the battery voltage when you apply an electrical load?
The only other possibility is battery isolator switch faulty.
Click to expand...

Battery voltage doesn't noticeably drop, but they're very large batteries (2 × 270Ah) being supplied with 20-30A from wind and solar and also supplying power for liveaboard requirements for a family of 4. I have already eliminated the isolator switch.

I have come to the conclusion that the batteries are fubarred, and there are new ones arriving in a few days.
 
roaringgirl said:
I tried removing wiring from the equation by doing it at the battery and got the same result, so although it seemed like wiring, I don't think it is.

When I tried it just now, the solenoid clicked once when I pressed the button, but then wouldn't click again on subsequent attempts. The same happened with my tests with the solenoid at the battery itself, even though there wasn't much discernible voltage drop under load.
Click to expand...

Have you tried connecting it direct to rule out possible solenoid problem?
 
Graham376 said:
Have you tried connecting it direct to rule out possible solenoid problem?
Click to expand...


I wonder if he realises what you are asking. IE connect the battery to the terminal on the solonoid where the starter motor wire is connected. Not the usual battery terminal on the solonoid. Maybe this is what was done on the other boat. Beware that doing this the motor will spin without the solonoid operating so watch fingers.

If this works then the solonoid could be faulty and a new one obtained from a good motor factor. Take youor old one with you.
 
Bilgediver said:
I wonder if he realises what you are asking. IE connect the battery to the terminal on the solonoid where the starter motor wire is connected. Not the usual battery terminal on the solonoid. Maybe this is what was done on the other boat. Beware that doing this the motor will spin without the solonoid operating so watch fingers.

If this works then the solonoid could be faulty and a new one obtained from a good motor factor. Take youor old one with you.
Click to expand...
See above
 
roaringgirl said:
When I tried it just now, the solenoid clicked once when I pressed the button, but then wouldn't click again on subsequent attempts. The same happened with my tests with the solenoid at the battery itself, even though there wasn't much discernible voltage drop under load.
Click to expand...
Does the battery supply any other lower drain devices?
If so, are they working ok?
Your problem sounds to me like a high resistance connection.
Have you removed and cleaned (wire wool) the battery terminal connections and any other connections in the path to the 'high drain' devices?
 
In the past batteries use to slowly die , now, one can give good readings but have no capacity. think would start a car perfectly, but turn off and have another go, no chance, yet plenty of apparent voltage. It seems the effective area of active plates is the size of a postage stamp.
 
If your battery voltage isn't dropping when a substantial load is applied then it's likely that the load isn't being properly connected to the batteries, as you should see a drop. So a poor connection seems likely or as others have said a fault with the winch, however I'm not familiar with anchor winches so can't really comment on them.

Try connecting an alternative load, the bigger the better within reason, and see what happens to the battery voltage; both the initial volt drop and then voltage drop over time. That should give a reasonable idea of how healthy your batteries are and if your winch/winch circuit are the cause of the issue.
 
I c
Medway Matt said:
If your battery voltage isn't dropping when a substantial load is applied then it's likely that the load isn't being properly connected to the batteries, as you should see a drop. So a poor connection seems likely or as others have said a fault with the winch, however I'm not familiar with anchor winches so can't really comment on them.

Try connecting an alternative load, the bigger the better within reason, and see what happens to the battery voltage; both the initial volt drop and then voltage drop over time. That should give a reasonable idea of how healthy your batteries are and if your winch/winch circuit are the cause of the issue.
Click to expand...

I took the motor out of the windlass and tested it on someone else's boat - it worked fine, so the windlass is not the problem.

I tried a new solenoid on my boat and it exhibited the same behaviour - it clicks, but the motor doesn't turn. Repeated attempts result in the solenoid no longer clicking.

I wired the solenoid directly at the battery and did the tests again, to eliminate most of the wiring to the bow... same behaviour.
 
roaringgirl said:
I c

I took the motor out of the windlass and tested it on someone else's boat - it worked fine, so the windlass is not the problem.
Click to expand...
Presumably you have considered that the windlass may be seized up in gearbox. If it will not move the motor will draw large current but not turn. OK if you remove the motor. ol'will
 
Hi. On these, there is a huge current draw, as you’ve mentioned. But I’d be tempted to put a meter across the huge in line fuse and solonoid to see what’s happening. Or even run a battery direct onto the windlass side of any switch, fuse or solonoid gear.
 
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