Nasa Marine BM-1: Shows "Discharging" when being Charged

[hoppy]

Over the weekend I fitted the nasa marine BM-1 battery monitor to the house bank (2x100amp). It works as I expected when I am using the battery, drawing 0.4amp with just one light on and shooting up to about 5.0 when all lights, instruments and fridge are on. When I ran the motor, the voltage increased up to around 14v and it was showing a charge of something like 10amps.

However when I turn on the shore power charger, the voltage head up towards 14v which is fine, but the amps "discharge" jump up around 10amp, rather than showing a "charge".

I'm not sure if I have ballsed something up with the install. Whilst all the cables for the positive dissapear into the engine bay to cause confusion as to how it is wired up (I assume the link between the two positive tterminals go via the power switched), the negative has just two cables, one joining the two negative terminals and the other dissapears off to the engine bay. I connected the shunt to the latter, which I think is correct.

I did make a mistake when I powered up as I had the shore charger on when the instructions say to not charge to start with. I could imagine that this mistake may screw up the BM-1's estimate of capacity, but it does not make sense otherwise. The fact that it seemed to work correctly when the shore charger was off and the motor on make me think that I connected it up correctly.

I do wonder if it is possible that the battery charger is wired up in a funny way to cause this, but I really do not have a clue.

I did go into the "engineering" menu to set it to 200amp and when everything is off, no current draw is shown.

I did notice that when the shore charger is on, the charge would go to 100 or even 105% bt when I turn the charger off it fairly quickly drops to close to 50% but then settles there.

Any clues, because I am lost (and now 1200nm from the boat)???

[CharlieJ]

However when I turn on the shore power charger, the voltage head up towards 14v which is fine, but the amps "discharge" jump up around 10amp, rather than showing a "charge".

Sounds like you have the shunt wired incorrectly. Note that their drawing shows all sources and loads on one side of the shunt and only the battery bank negative to the other side of the shunt. Of course the sensing wires have to be correctly wired also.

Charlie

[hoppy]

Originally Posted by CharlieJ

Sounds like you have the shunt wired incorrectly. Note that their drawing shows all sources and loads on one side of the shunt and only the battery bank negative to the other side of the shunt. Of course the sensing wires have to be correctly wired also.

Charlie

This is where the diagram was a bit confusing as they had no diagrams for multiple house batteries in parallel. I have my shunt mounted on the battery that connects to the load. Should it really connected to the last battery in the parallel chain, the only one with a single negative (connected to the other batteries negative)??

[Pete7]

Hoppy yes, at some point on a multiple bank you will end up with a single black wire which ought to go to a distribution point. You might want to check that someone hasn't added anything else to any other batteries.

What's really odd is that it works properly when the engine is running.

I wonder if there is a fault with the charger? have you used it much and know that it really does charge the batteries up or has the BM1 discovered an unknown fault perhaps.

Some back ground reading:

SmartGauge Electronics - Interconnecting multiple batteries to form one larger bank

Pete

[Pete7]

Just a thought, were does the negative side of the battery charger connect to? distribution point/bus bar or directly to a battery?

Pete

[hoppy]

The boat has not left the dock since I bought it at the start of winter, so I have only run the engine a couple of times for short periods since December. I have however spent a bit of time onboard with shore power connected and the charger on. Never had any power problems.

I might need to try and trace where the charger cables are connected.

Thanks for the link, will read it tonight. I have a feeling that "method 2" is how mine is wired up.

[hoppy]

Originally Posted by Pete7

Just a thought, were does the negative side of the battery charger connect to? distribution point/bus bar or directly to a battery?

Pete

No idea at the moment. I have to wait until April 30th before I am back on board. Happily I will have 5 days of sailing in between my attempts at following cables around

[Pete7]

Originally Posted by hoppy

Thanks for the link, will read it tonight. I have a feeling that "method 2" is how mine is wired up.

Yes, as is our 2 x 110 AH battery house bank after I read that article.

Pete

[hoppy]

I just dug up a photo I took of the house batteries when I first inspected the boat. It has me thinking that one of the two smaller red cables is the cause of my "issues".

Now I have to wait 18 days before I can try to figure out what they are

[Pete7]

Yep, recon you are on to it, its supplying power that isn't going via the shunt or when the charger is on the two separate positive feeds are confusing the BM1.

Can I make a suggestion, are they the only batteries on board? If so you are using two huge batteries, one for the house and one for engine via a 1/2/both/off switch. You would gain a huge increase in capacity if both house batteries were wired together into one bank and you fitted a small extra battery for the engine. The engine battery doesn't need to be anything special and a small one will be fine, think euro diesel car engine battery. You can still use the the 1/2/both switch and BM1.

Pete

[hoppy]

The boat has 3 batteries the same size, two for the house and one for the starter.

I was just checking the owners manual and noticed that a 3rd house battery was a Jeanneau option with the 3rd battery sharing the same compartment as the starter.. nice to know

I can't seem to find the charger on the wiring diagram, so I am not sure how it should be connected. However the diagram does not show any extra cables connected directly to the batteries, so the small cables must be non-standard.

The wiring diagram does show that the batteries should be connected using method 2, but I do wonder why all 3 visible red cables disappear into the engine bay rather than 1 off to the switch and a 2nd joining the two batteries.. unless the cable joining the two just briefly disappear.

So frustrating not having easy access to the boat but then again the water in Greece never freezes over.

[sv-Mystique]

I have the same monitor and having difficulty with Amps and charging state? I have two 4ds and have the expected amps set at 395. I have the shunt and power connected on the battery without any other connection. The start battery is wired separately and I have it connected as described, the volt side works perfectly just the amps and state are not in sync.

Thoughts?

[dnickj]

Hi

I have the same setup on my Jeanneau
Your problem is the small blue wire on the -ve battery terminal
This is the neg from the battery charger
Rewire so this is connected to the load side of the shunt then all should work

[sailinglegend]

With a battery monitor installed that has the shunt in the negative cable the shunt becomes the new negative post for the service bank, so the starter battery negative must also be connected to the bus bar, not to a service battery negative terminal. This error is probably one of the major causes of battery monitors not reading the charging amps.

This will often happen when the starter bank has priority and is charged first because the charger positive and negative cables will be connected to the starter battery. When the split charging system supplies positive volts to the service bank the negative return goes via a service battery negative stud and then the starter battery negative stud. This will bypass the shunt. For the battery monitor to measure the service battery charge the negative return to the charger must go via the shunt and then to the starter battery negative post.