Strange Nasa BM1 problem

Bilge Rat said:
Don't know if it helps but we've fitted two of these and in both cases, we never saw any difference whether the backlight was on or off. I know of people who've had troubles but this always seems to be down to having something connected to the wrong side of the shunt. I'm thinking that may be pieter2 has a faulty instrument. Have you been in touch with NASA to see if they've seen this fault before?
Click to expand...

Really it is not easy to reproduce in normal usage. You need to switch OFF all loads and chargers and check what happens if you switch BM1 light ON. In normal usage, with loads applied, there is no difference with light ON or OFF.
One important data is that the current, nearly 3A, is CHARCHING.
Cheers
 
Reading this thread with interest. I've got a BM1, and stupid as this may sound I've never "zero'd" it, so I also get a very small discharge showing with no load. One to sort next time I am down.

However, I have another problem, which may or may not be related to the "nothing else on this battery post" issue.

When I leave the boat, I keep the bilge pump on auto, and the corresponding switch on my fuse panel "on". It's a "Seaworld" model, and has a little red light that is obviously drawing some juice. However I have a Forgen generator, which I was always told to crocodile clip onto the +/- terminals of the dom battery. However, without exception the dom battery is always knackered when I return to the boat after a few weeks, and it was new last year. (and fortunatly it's nothing to do with the bilge pump having to run...she is a very dry boat). It charges fine under engine too.

So...where should I connect the Forgen? (2 battery setup, off/both/1/2 switch)

Do I connect a mains charger to the same place?

Why is the forgen not charging, surely it should keep up with the needs of one ickle lamp on my switch panel? (it's kicking out 14v in a medium breeze according to a multimeter across the croc clips...obviously off the battery!)

Any thoughts? BM1 related or something different?
 
So, my problem looks the same like lula's?
Here you have my electrical schedule. I am not technical, so forgive me the wrong symbols, etc. I wrote down the names/functions of devices, switches, etc.
The photo's are not really clear, but the schedule is, I hope.
I wonder if there might be something wrong becuase of using two different batteries (the start battery is quite old). When I put off the Ctek would the domestic battery load the start battery through the Ctek or through some connection in a moisture area (bilge pump or something). Would that explain the 2,6 A - 3,0 A discharge with backlight off and 0,0 with backlight on?
 
I am afraid your wiring is incorrect. The shunt will measure the current from the start battery as well as the domestic battery. Look again at the diagram that VicS provided and compare to yours. The shunt should only be in the domestic battery circuit. The start battery negative connection should by-pass the shunt and connect to what you have shown as the 'earth' point.

I also still do not understand why your white/black/yellow voltages are as you report.

Have you checked the crimp connections as suggested earlier?
 
Playtime said:
I am afraid your wiring is incorrect. The shunt will measure the current from the start battery as well as the domestic battery. Look again at the diagram that VicS provided and compare to yours. The shunt should only be in the domestic battery circuit. The start battery negative connection should by-pass the shunt and connect to what you have shown as the 'earth' point.

I also still do not understand why your white/black/yellow voltages are as you report.

Have you checked the crimp connections as suggested earlier?
Click to expand...

Yes Playtime, you're right, the starter battery ground in the Pieter2's diagram is incorrect.
Anyway I understood Pieter2's problem is 2-3 A of DISCHARGE and in my case is CHARGE. Could be the problem that the starter is charging the domestic in one case and the domestic is charging the starter in other? Across which wire?, obviously the return is over the shunt. Why?
Cheers
 
The starter battery negative circuit needs to be rerouted as per the NASA (and VicS) wiring diagram.

It is possible that sensing the starter current (100's of amps) through the shunt has caused the offset problem.

However, the problem with the voltages measured across the white/black/yellow leads needs to be resolved. As measured the voltages are 'impossible' if the wiring is correct, therefore there must be something wrong with the wiring in this area.

I say again, please check the connection of the 3 thin wires (white/black/yellow) to the shunt and back to the meter, particularly the integrity of the crimps.
 
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While we're discussing the wiring connections, am I the only one bemused by the "loading lamp" and "engine start button" in the wire to B+ of the alternator? And the negative for "plug steering machine" should go to the earth side of the Nasa shunt. And ideally, the positive for "plug steering machine" should at least go to the switched domestic feed.
 
I was on the boat this afternoon and can report that, on my installation, turning on the BM1 backlight has no measurable impact on the indicated current. With no load, this remained exactly at zero.

FYI my installation is as per the attached photo. The starter battery is the Varta; the shunt is on the right and the 2 service batteries are at the bottom.

The sense leads on the shunt (yellow and white/black) are clearly visible. The main boat 'earth' is the negative pole of the starter battery. Only the service battery circuits are sensed by the shunt.

Pieter - where were you measuring the voltages across the white/black wires? On my wiring loom, as received from NASA, these are securely crimped together. The voltage between white and black must be zero if this crimp is sound. Similarly, the voltage between yellow and white, and yellow and black should be equal (and proportional to the current across the shunt).

Any other readings must indicate a wiring error.
 
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@Playtime: I have read the voltages on the terminal black, just behind the BM1 display, So where the wires black and white are NOT connected with eachother!
See photo below. On the shunt the black and white wire are connected with eachother in one crimp.
 
pieter2 said:
@Playtime: I have read the voltages on the terminal black, just behind the BM1 display, So where the wires black and white are NOT connected with eachother!
See photo below. On the shunt the black and white wire are connected with eachother in one crimp.
Click to expand...

OK then it is fairly obvious that somewhere in the circuit the black and/or white wires are not connecting as they should.

As suggested before, please check the single crimp where the black and white wires connect to the shunt.

Secondly, double check the connector block shown in your photo - maybe one of the wires is not actually connecting properly here, for example, you may have screwed into the insulation and not the wire. This is quite easy to do and looks like a good connection when in fact there is no connection.

Good hunting :)
 
Please look at answers below

Playtime said:
OK then it is fairly obvious that somewhere in the circuit the black and/or white wires are not connecting as they should.

As suggested before, please check the single crimp where the black and white wires connect to the shunt.
THIS I WILL DO ASAP

Secondly, double check the connector block shown in your photo - maybe one of the wires is not actually connecting properly here, for example, you may have screwed into the insulation and not the wire. This is quite easy to do and looks like a good connection when in fact there is no connection.
THIS I ALREADY DID (TWICE).

Good hunting :)
Click to expand...
 
As suggested before, please check the single crimp where the black and white wires connect to the shunt.
Click to expand...
This is beginning to look more and more likely to be the place where the trouble lies. One of those wires is the negative power supply to the BM1 and a bad connection will give rise to a small voltage accross the connection. I think this would show up as a charge current being displayed.
We are looking for something that gives a reading of 3amps. IIRC the shunt is 50mV per 100amps so were are only looking for 1.5 mV
Earlier we were looking at 1.2 mV between yellow and white/black when there should have been zero.

Is this it ?

I'd clean and remake the connection between the crimp and the shunt and then if that did not solve the problem I would cut off the crimp and remake it or even solder the black and white wires onto a suitable ring terminal.

(Crimped terminals I dont like! I hear all the objections to soldered connections but done properly you get a 100% good connection!)
 
wrong schedule

Someone noticed a mistake in the schedule as given by me, some posts earlier. It does not interfere with the problem of the NASA, but just in case someone would use the schedule at some time for other purposes, here you have a more correct version (connections with relay / loading lamp are changed)
I will keep you informed about the new black-white connection!
 
pieter2 said:
Someone noticed a mistake in the schedule as given by me, some posts earlier. It does not interfere with the problem of the NASA, but just in case someone would use the schedule at some time for other purposes, here you have a more correct version (connections with relay / loading lamp are changed)
I will keep you informed about the new black-white connection!
Click to expand...


Yep you have corrected the warning light ( "loading lamp") to alternator connection and the alternator output to the split charge control relay but your representation of the engine starter circuit is a bit over simplified.
It was the engine start button and loading lamp that caught my eye. PVB's too I imagine.

Don't forget that the connection of the starter battery negative and the autopilot ( "steering machine") are still incorrect.

Below shows how the start battery negative and the autopilot negative should be connected

 
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Hi all,
To add more information: I have checked today all the installation and I can afirm that the stratnge 3A also appears when the loads are applied, the charger working and the boat in normal situation. If light ON in the NASA BM1 is pressed there is a change of the current showed by it in 3A (charging).
I hope this help and somebody found a solution.
Cheers
 
Perhaps someone will print out this thread and take it with them to the boat show.
Nasa stand A29
 
BM-1 Inline fuse is a potential problem!

I've been on my boat today, and one mission was check some of these weird reported happenings.

My batteries had been fully isolated, and even the BM-1 disconnected (as I don't like the small drain over several months). On reconnecting the BM-1 I was rather surprised to see the domestic battery bank showing 11.1v ...NOT GOOD ... although not impossible as 3yrs old and sometimes they can die a sudden death especially in the cold we've had.

However when they happily started the Eberspacher (engine not yet started), and then on charge dropped to a charge acceptance of 3A in a few minutes (at 14.8v) something was obviously fishy! I then tried PIETER2 's thing of turning the backlight on and off. The indicated voltage varied all over the place (though I didn't observe any change in current or AHr indications.)

It only took a couple of minutes and a decent test meter to determine that the problem was the inline fuseholder in the red (permanent) feed to the battery +ve. (the spring-loaded type are notoriously unreliable at both high and very small currents......I will replace with an inline blade type).

Not quite the same symptoms as PIETER2, but something to watch out for if you get strange readings.

Vic
 
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