1.5 amp discharge with everything turned off ?

[grafozz]

There seems to be something drawing power on board when everything is turned off and it causes a drain
on the 2 x 85 amp hour batteries ,
the monitoring is done by a BM1 guage and the drain stops when the batteries are switched off ,
also there is an 80 watt solar panel charging these 2 x batteries which is putting in 19 + volts .

can anyone explain how to find out where the 1.5 amps is running off to , please ?
it keeps setting off the low battery alarm .

 

[NickRobinson]

Can you disconnect physically beyond the shunt? That should prove whether it's a real or reported 1.5A

Alternatively place a trusted meter between the disconnected battery terminal and its connecting wire to see if it really is a drain of 1.5A

My BEP meter needed zeroing, a task quite hard to master from the book but eventually successful.

Nick

 

[sarabande]

have you a clamp ammeter ? Or can you borrow one ? Is there a diode in the solar panels (to stop the batteries feeding the panels when it's dark) ?

Assuming the meter is reading OK:

with everything you can see switched OFF and the panels disconnected, test each piece of wiring running from the batteries first of all. Then from the switchboard. Any 'live' feed will show up.

At about 18 watts, that drain will hammer those batteries in a couple of days without any recharge.

It is most likely to be a wire attached directly to the batteries, so perhaps a light in the engine room, small fan, masthead light...

 

[AndyJ76]

Do you have the solar panels connected to the batteries directly, or via the "load" side of the shunt?
Is the shunt connected to the "load" side of the isolator switch?

If the solar panels are connected to the battery side of the shunt instead of the load side, then they will see the charging current as discharging current. (I get this from my alternators because they are wired directly to the battery, bypassing the shunt)
Turning off the isolator isolates the shunt from the batteries (giving you your zero current), while the solar is still merrily charging away in the background

1.5 amps is about what I'd expect from an 80W panel too

 

[grafozz]

the solar panel is connected to the regulator , in , ( solara ) then the "out " straight to the batteries , which seems to be the advised method ,
so I dont think it involves the shunt ?

there are neg and pos terminals in the engine bay ( bolts ) feeding engine and up to the switch panel where all the boat electrics are fed from via fuses .

it was a long time ago when the BM1 and shunt were fitted but it was done according to NASA instructions .

I searched the forums and it seems that if I switch off the batteries to stop the drain , then the solar panel will not be able to charge the batteries anyway , is this correct ?

 

[AndyJ76]

Not if it is connected to the battery side of the isolator. The circuit is the regulator and the battery.
Connect the regulator to the load side of the shunt and it will read properly

 

[sarabande]

IMHO you need to get some 'as installed' circuit diagrams set up.

This will make any future maintenance much much easier, as well as making it possible to answer this fully.

If the panels go from the solar panels to the batteries, i.e. are connected without any further deviations, then the batteries will be charged when the panels are active. Switching off the batteries is achieved 'downstream' of the terminals, and will not affect the charging from the panels.

I'm not sure how diodes can fail to allow reverse flow, but it might be possible that when the panels are not producing power, there is power flow back to the panels. You can check this by covering them up completely when the sun is shining, and seeing what happens to the charge rate.



Have you tried tracing where all the small cables go from the batteries? I don't mean the main, thick, power cables, but any little ones.

Are you sure the meter is accurately zeroed ?

Have you borrowed a clamp ammeter ?

 

[AndyJ76]

The problem is that the shunt reads the current by observing the voltage across the shunt. Because the panels are charging the battery, the voltage is higher on the battery side than the load side, which looks like a discharge.

 

[halcyon]

Not if it is connected to the battery side of the isolator. The circuit is the regulator and the battery.
Connect the regulator to the load side of the shunt and it will read properly

As the shunt is in the neg side, this needs checking for solar panel earthing location, is it battery side of shunt also cover the solar panel, if the drain falls then at least it must be the solar panel, no change and it's a bigger hunt.

Brian

 

[VicS]

the solar panel is connected to the regulator , in , ( solara ) then the "out " straight to the batteries , which seems to be the advised method ,
so I dont think it involves the shunt ?

there are neg and pos terminals in the engine bay ( bolts ) feeding engine and up to the switch panel where all the boat electrics are fed from via fuses .

it was a long time ago when the BM1 and shunt were fitted but it was done according to NASA instructions .

I searched the forums and it seems that if I switch off the batteries to stop the drain , then the solar panel will not be able to charge the batteries anyway , is this correct ?

Here is a diagram I drew some time ago because of the confusion over the correct way to wire a NASA battery monitor, although the instructions and diagrams now on line and in the manual are less ambiguous than they were.

Where it says no other connections ... it means no other connections!

The output from the positive terminal of the solar regulator should go direct to the house battery positive ( via a fuse) so that charging can continue when the isolator is open. The negative goes to the same place as all the other negatives ... not directly to the battery negative.

Later versions of the BM have an additional connection ( an orange wire) which can be connected, via a fuse, to the starter battery positive to enable its volts to be displayed.

 

[VicS]

The problem is that the shunt reads the current by observing the voltage across the shunt. Because the panels are charging the battery, the voltage is higher on the battery side than the load side, which looks like a discharge.

If the battery monitor has been wired correctly and the negative of the solar panel output taken to the same point as all other negatives ( neg bus bar perhaps ) and NOT directly to the battery negative a charge current from the solar panels will be displayed as a charge current, just as the output from the alternator, wind turbine or battery charger will be.

If the solar panel negative is ( incorrectly) wired directly to the battery negative the charge current will bypass the shunt and will not be displayed. Neither as a charge current nor a discharge current.

I recommend you study the wiring diagram above or on the NASA website

 

[AndyJ76]

I find it suspicious that the discharge current matches what I would expect as the charging current of the panel.

As halcyon said, try covering the solar panel and see how that affects it.

VicS, that's not the situation with my alternators.

 

[VicS]

VicS, that's not the situation with my alternators.

You need to study the wiring diagrams carefully and wire your system accordingly. A battery monitor is hardly going to keep even a vague track of the state of charge etc if it has been wired in such a way that it sees charge currents as discharge currents.

 

[AndyJ76]

I've wired my system so that the engines will start, which is far more important than the charge tracking (which is a joke anyway, see the other thread).
The shunt is not capable of supporting the current required by the starter motors, so I had to bypass it for the engines.

The BM-1 registers a discharge current when the alternators are running for the reason I described earlier. Of course, you'd expect the shunt to not see the difference, if the negative side of the loop is at a 0v reference, but this isn't quite the case (otherwise the shunt would be shorted out)

 

[Trundlebug]

I've wired my system so that the engines will start, which is far more important than the charge tracking (which is a joke anyway, see the other thread).
The shunt is not capable of supporting the current required by the starter motors, so I had to bypass it for the engines.

The BM-1 registers a discharge current when the alternators are running for the reason I described earlier. Of course, you'd expect the shunt to not see the difference, if the negative side of the loop is at a 0v reference, but this isn't quite the case (otherwise the shunt would be shorted out)

Something a bit wrong there!
The BM1 is not designed to manage starter battery currents, either in or out, just the domestic bank. If you have your system set up correctly, you will have a separate starter and domestic bank, as in VicS's diagram above. If you just have several batteries in parallel used as both starter and domestic, that's not what the BM1 is designed for, and isn't a good set up so you won't get the best out of what you have.

The very fact you have a discharge showing when the alternators are running says something is wrong. As Vic said, you've no chance of managing anything like that. My suggestion would be, take the time to rewire to the diagram above. It works. Properly.

 

[AndyJ76]

It works just fine.
The only difference is that my battery banks have the negatives paralleled together, rather than the engine start negative going to the negative bus bar.

The discharge current that I see when the alternators are running is actually the charging current. It surprised me the first time, but it's easy enough to live with, seeing as most of the time the engines are off.

It also a reasonable explanation of what the OP is seeing, which was the point.

 

[Trundlebug]

Each to their own, but you're not getting the benefit of one of the key features of the BM1.
It will count how many Ah you've used whilst moored / anchored up. When you get going, although the bar graph at the side will indicate state of charge as a %, that's a very rough indication. However because it will count also how many Ah you've put back in (if wired correctly) it will count how many AH have been charged and you can tell where you're up to. With your set-up that's not possible.

Also, if you have the alternators showing a discharge, how do you know if when you turn something on it's adding to or reducing the discharge?
I appreciate your engines start OK, but they would too if set up correctly in VicS's diagram above. And you don't need a BM1 at all for the engines to start!
Not sure why you're happy with a far from perfect set-up, but good luck to you.

 

[VicS]

It works just fine.
The only difference is that my battery banks have the negatives paralleled together, rather than the engine start negative going to the negative bus bar.

The discharge current that I see when the alternators are running is actually the charging current. It surprised me the first time, but it's easy enough to live with, seeing as most of the time the engines are off.

It also a reasonable explanation of what the OP is seeing, which was the point.

The NASA Battery monitor is designed to fully monitor the house battery only. It is not intended to monitor startting currents although it will, i understand, accurately monitor but not display currents a little in excess of 100amps. The limit will be the max current which the shunt can withstand.

I can follow your logic in connecting the both battery negatives and the engine negative all together so that the shunt is bypassed to enable either battery can be used for starting but this surely means that the alternator output is also bypassing the shunt. That being so the battery monitor will register it as neither charge nor discharge. What you see as a discharge must be the current being used by other circuits.

Trying to explain what the OP is seeing based on your interpretataion of the readings you see on your nonstandard wired system is not reasonable. It is adding to the confusion

 

[Trundlebug]

There seems to be something drawing power on board when everything is turned off and it causes a drain
on the 2 x 85 amp hour batteries ,
the monitoring is done by a BM1 guage and the drain stops when the batteries are switched off ,
also there is an 80 watt solar panel charging these 2 x batteries which is putting in 19 + volts .

can anyone explain how to find out where the 1.5 amps is running off to , please ?
it keeps setting off the low battery alarm .

The only explanation I can suggest is, have you checked your bilge pump?
Quite often bilge pumps are wired such that they will still work even when everything is turned off.
If you have a seized or blocked bilge pump, and a switch has stuck, it may be that.

 

[AndyJ76]

The "discharge" current only appears when my alternators are running. For example, if I remove the bulbs from the alternator warning light, such that the alternator field coil doesn't excite, no discharge.

I'm pretty confident that what I see is due to the relative location of the 0v reference. On my setup, it's on the battery side, and in yours, it's on the bus bar.

If the OPs setup is as I originally described, then he may be seeing the same issue as I am (except in his case, he can move the solar onto the bus bar side to fix the problem)
And if it's not, then what I've said is irrelevant and can be ignored.