1.5 amp discharge with everything turned off ?

[VicS]

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.

If his solar panel negative is connected directly to the battery negative (or the battery end of the shunt) the current will bypass the shunt and it will not register as either a charge current nor as a discharge current!

I'm not sure why you are concerned about the "0 volt reference" The current flowing through the shunt will produce a potential difference across the shunt. Its magnitude will be proportional to the current and its polarity will be determined by the direction of the current flow. A charge current will make the battery end of the shunt positive with respect to the other end whereas a discharge (or load) current will make the battery end negative wrt the other end.

That means that if you take the battery end as 0v a charge current will make the other end slightly negative while a load current will make the other end slightly positive.

Thinking about your system. Is it possible that your alternator has an insulated negative ? If so it would enable the two batteries to have their negative terminals connected together and the engine starter negative ( and cylinder block possibly) connected to them and for the alternator negative to be connected via the shunt. That way the starting current would bypass the shunt while the alternator current would pass through the shunt and be registered by the monitor. If that is the case there is no reason why it should not be wired so that a charge current is displayed as a charge current while a load current ( lights etc) when the engine is not running shows as a discharge.

As it is how does a load ( lights and whatever else you have) display when the engine is not running? As a charge or as a discharge?

 

[grafozz]

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.

I have checked the bilge pump and its ok , the float switch also operates ok .

another point which may help you guys identify the problem is that after running the engine the "amps in " reading on the BM1 is always 0 yet when its running it shows a charge going in so maybe it is wired the wrong way ?

I will take VicS diagram down and check
thanks everyone for the advice .

 

[grafozz]

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!

ah , now I have a bus bar on both neg and pos and the BM1 is wired to

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.

ah ,now I have + and - bus bars and the BM1 is wired directly on to those terminals ,
so I will move the neg straight to the battery and see what that produces , thanks .

 

[AndyJ76]

As it is how does a load ( lights and whatever else you have) display when the engine is not running? As a charge or as a discharge?

Everything except the alternator reads as you would expect. I've wired solar, wind and mains charger to the bus bars, and when charging, the BM-1 agrees with the figures on the controllers. I can also tell what is currently switched on using the BM-1. For example, the fridge uses about 4.2A, so I can tell when it's running.

 

[halcyon]

Everything except the alternator reads as you would expect. I've wired solar, wind and mains charger to the bus bars, and when charging, the BM-1 agrees with the figures on the controllers. I can also tell what is currently switched on using the BM-1. For example, the fridge uses about 4.2A, so I can tell when it's running.

If you start engine, then turn on power, cabin lights etc, does the reading alter ? does revving the engine make a difference ?


Brian