Where is our 3 amps going?

[adarcy]

There appears to be a 3 amp drain in our boat with the batteries isolated, where is it going /being used ?

We have a Princess 45 onshore awaiting new side window frames (£££££!). When I came back to check on it, "someone" had left the domestic battery bank ( 4 x 12v 115 a/hr connected as 2 x 24v ) connected as they were flat, showing approx 3volt. The dehumid was running on the mains 240v and the battery charger
was switched off to prevent overcharging (unfortunately). I checked nothing was switched on and started the charger which only showed 4 amps with the engine start battrey bank (2 x 12v 115 a/hr in series) switched in or out. I left them switched out in case the charger is not clever enough to avoid overcharging.
Normally one would get the max charge of 40 amps which is its rating so I suspected the batteries were beyond help. On my return 48 hrs later, the stench (? hydrogen) was terrible and 2 batteries were hot and 2 warm. It was still charging at 10 amps, usually it settles to below 2 amps. Fearing they were all b*****d I disconnected them and returned 3 days later. The engine start batteries were fine 25.5v but the domestic bank only 20.5v i.e. 85% discharged. After discussion with co-owner, I charged them for another 90 mins
and then isolated them and took out the bridges between the batteries in the banks i.e. each 12v battery had an unconnected post. On return yesterday, the volts were 3.8 10.9 13.0 12.8. So we thought we had 2 good ones, 1 rather doubtful and 1 useless. So we put the 2 good ones in as a single 24v bank set the
charger 12 amps and went off to the pub. Later came back, charger off 10 minutes to settle and they showed 25.5v, we thought we'd try and live with half the normal battery capacity for next year ( the windows will be v expensive) and just monitor whether the 3rd battery continued to dischage or not.

When we connected up again, there was a BIG flash. As in the immortal words of our inimitable and sorely missed contributor matts " ooh er don't fancy that ". The multimeter showed there was a 9 amp drain - no wonder the original bank had gone flat! Investigation showed that this time it was my fault, I had left the
solenoid connected but "nothing" was switched on, no lights, the dehumid on the mains and the VHF had not been reconnected so we hunted for anything taking power. Disconnecting the alarm system made no difference on the digital multimeter. We remembered the GPS is wired in permanently and dies as soon as the isolater solenoids switch out so we thought the GPS internal battery was probably useless and may be consuming power. Unhooking that reduced the drain from 9 to 6 amps. Switching off the solenoids and retesting the drain was still 3 amps.

Where are the 3 amps going ? that is still 72 watts, enough to light a bulb and enough to drain a 230 a/hr battery bank.

We presumed the difference from 6 to 3 amps was the solenoids and any relays being powered when the batteries were not isolated but cannot work out where the 3 amps go when the batteries are isolated. With the domestic batteries disconnected the bilge pumps work on manual operation and the bowthruster also, so they must be powered from the engine start bank, which is fine. We do not have an anti-corrosion powered setup like on our v old mercruiser dayboat.

What else can we check ? All suggestions gratefully received.

Anthony

 

[Guest]

I see you have 24 v system, are all the batteries disconnected from each other? if not then I suspect you have a dud one with dead cell which will draw from good battery with higher voltage. Separate them all and drop test with hydrometer for low cell level.

Paul js.

 

[Bergman]

How are you measuring the current, 3 amps into a GPS sounds awfully high, the poor thing will be fried.

Similarly 6 amps into anything not obviously using the power for something useful is quite a serious current, certainly enough to start a fire, enough to start several in fact.

Think I would start by double checking the measurements, perhaps with another instrument.

After that its disconnect things till it stops and the last thing you disconnect is the guilty party - usually.

 

[longjohnsilver]

3 amps into GPS presumably when it's turned off is about 3 x more than when it's on. That's not possible, have you checked to see if anything is shorting out somewhere along the line? Check the batteries as already mentioned, suspect they're the root cause.

 

[hlb]

Test transmision.
But my boats conected to mains all the time. Batteries charging all the time. Last saw boat in September. Must admit. many phone calles to mechanic, to make sure all is well. But cant see problem with proper charger. Not a halford thingy.
My chargers on all year round. Just gives them a bit when they neeed it.
(Is this OK kim, I'm doing my best.)

Haydn

 

[greystones]

Hi, just a thought but if your main cables insulation are damaged or in the process of decay ,it is possible to get leakage between the cables ( a high resistance short).if you can get an electrician with a megger this will check the insulation res of the installation.if they are you will need to rewire as this could possibly cause overheating at the site with serious implications. Some of the other spots could be crimped cables going thru bulkheads ,cables near heaters, anywhere where cables can be squeezed .
just a thought.

 

[DavidJ]

I like Pauls reply,do that before the suggestion below.
If one of the diodes on the alternator has gone open circuit it will drain the battery and may only show a small loss of power in Alternator charging
David

 

[Guest]

Yes both good suggestions ,it may be a build up of sediment in the batteries allowing the cells to leak to each other .
On the old style batteries you could cut the pitch sealing and lift out the cells ,great way to clean .
Over charging ? causes lots of problems .
Re putting a mega meter on !!!!!!!!!!!!!! what about the risk of damage to any thing electronic .
Some times you can when able to, check the wiring by inserting a sharp needle into the cable it self and for example find localised resistance due to an internal short !!.Quite handy if you have 50 ft of cable to check.
I don't envy you
Mick

 

[adarcy]

Paul

Thanks for your interest. I am sorry if I didn't make it clear.
We did disconnect the 4 batteries and then saw the voltages drop so we knew which 2 good ones to use. It was only when trying to reconnect them up after recharging that we found the flash and then investigated the drain. It's the amount of power the boat circuit is draining that is the problem.
BTW we did allow 2 mins of connection time and then took the post off and remeasured the drain so we think it is not due to the 2 batteries in series "equalising their charges" but a true circuit drain.

I'm not trying to be smart but I think we can exclude internal battery shorts as a cause of the continuing loss but we also have at least one useless battery now - which remains disconnected.

Anthony

 

[greystones]

as regards the megger test .i did say consult an electrician who will know what to disconnect . I am One and have found problems like this with cables over a certain age or in certain conditions.
Cheers

 

[adarcy]

Re: Thanks for all the ideas

bergman, LJS, hlb, greystones, Davidj and mtb_carburetters

Thank you all v much for the ideas, I'll now try and root around them.


bergman
we only measured the 3 amps into the GPS by noting the drain with it connected and disconnected. As it uses a D-shell it is difficult to measure while it is "in". It is permanently live when the battery solenoids are on. We feel sure the internal battery is b*****ed as the GPS dies immediately the solenoids are switched out but it is a v old AP4 so it may not have much of an internal supply. However, we have taken it out for separate investigation but it deosn't explain our residual 3 amp drain. We checked the digi multimeter on both amp ranges and volts and the volts with a standard battery. The flash on connection leads me to believe there really is a substantial drain.

LJS
your ideas are as usual v helpful but as you can see above the GPS is now out of the game and I believe we have now excluded an internal battery problem.

Hayden
Yes you're right, we should have left it charging up as we used to, but I remember reading that one shouldn't leave a charger going without a tiny drain like one small internal light on and we did'nt want to do that while the boatyard men took the window out. Well one learns. we suspect they left the domestic bank solenoid on so it was drainig at 9 amps rather than 3 amps which has really smashed the batteries. We have never had any obvious draining of the bank when we have left the boat on the pontoon without power for 3-4 weeks before - so we don't really know how long the problem has persisted.

greystones
Oh dear, decay in cable insulation - don't like the sound of that. The boat is 13-14 years old and the plastic insulation on the main power cables doesn't appear to be brittle but..... Do tell, what is a megger? that's a new one on me and, as you would expect, the cable runs are not particularly accessable but at least there is no obvious visual problems with them. I'd hope to know a little more before splashing out on a whole wiring check if poss.
Just seen your follow-up post, can you hazard a guess about what age do you find cable insulation failing? Many thanks yet again.

DavidJ
I'm "fairly" confident Paul is not on the right track. However, your idea of a stuck diode is v interesting. Would we have to try and test it by disconnecting each alternator somewhere at the engine end and retest for the drain or might there be an easier way? Anyway, should it be relevant when the battery master solenoids are switched off? I don't know.

mtb - Mick
The batteries are only 2+ years old and quality jobbies ?Heckke ?Hokke (Merc/BMW original standard fit not cheapo aftermarket) but sealed plastic case. I feel sure the damage was caused by them going flat rather than overcharging. I don't know what a mega/megger meter is either but I think I'll leave sticking probes into ?suspect wiring insulation until last if you don't mind, after all holes in insulation can't help can they?

I had one dead-end theory over lunch that the only bit of electric equipment I had not considered was the fluxgate compass. The wiring has not been changed, the autopilot head is only active when the master solenoids are on and the nav instrument circuit is switched on. It might be deifficult to check any other way than disconnecting the fluxgate. Does anyone know if this would cause problems other than having to "reswing" it next year? I doubt v much if it takes 75watts but it may be shorting. With all your help, I'm trying to apply some logic rather than pull everything out/off to find the cause.

Thank you all again.

Anthony

 

[desG]

A few thoughts:
(1) On my boat, the only things remaining connected to the batteries when the isolator switch is off are the bilge pumps (when switch in the in auto position) and the output from the battery charger. Could the charger be faulty? Have you checked the drain with the output from the charger disconnected?
(2) I think that if the cable insulation had failed and was drawing 3 amp at 24 volts, you would have smelt/seen burning plastic.
(3) You should locate problem before leaving boat unattended with the batteries connected. If this power were dissipating in a confined volume it could cause a fire.
(4) All equipment and appliances should have switches or circuit breakers inline, so if they are all off you should be able to eliminate them as a source of the drain unless of course such a switch or cb is faulty. You could check the rear of the switches to see there is no voltage on the equipment side. However most equipment/appliances indicate they are running by the making noises or showing lights/displays. Thus it should not be necessary to actually disconnect each piece of equipment in turn. Just think what might not be in this category eg flux gate compass, autopilot.
(5) Any chance that there is water somewhere covering exposed 28volt connection. (Leaking side windows!)
(6) Don't use a megger on cable connected to electronic equipment. A megger is a high voltage insulation tester.
(7) Double check the meter is correctly reading amps eg by putting in series with a known load. I have wasted time chasing red herrings because of this. The flash could just possibly be a capacitor charging.

Hope you locate the problem soon.
Des