battery monitor

Sans Bateau

Sans Bateau

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Following my query over alternator size, I'm thinking of fitting a battery monitor. The cheapest as you all know is the NASA one, I also know lots of you have them fitted. But I also seem to remember some talk of problems.

Your comments and views please.
 
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Following my query over alternator size, I'm thinking of fitting a battery monitor. The cheapest as you all know is the NASA one, I also know lots of you have them fitted. But I also seem to remember some talk of problems.

Your comments and views please.

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Steve, I would go as far as saying this bit of kit does everything I need. Accurate too as it agrees with my STeca solar panel regulator. I have not heard of any problems with them. I would not be without it now as it tells you so much about your consumption and charging.

While you are installing this, you should check on your main battery cables. When I fitted the Stirling reg, it kept falling over. Cables all looked correct, but by putting larger cables in, I raised the charge rate from a max of 30 amps to 45amps, (50 amp alternator) and solved all the Stirling problems - obviously they were nothing to do with the Stirling, but the BM monitor was essential in the process.

Chris
 
My understanding of this unit is that the shunt is rated at 100amps. It is possible that if your wiring configuration is set up such that you can start the engine from the domestic battery (which arguanbly it should be) then the shunt will be exposed to a larger current draw than that for which it is designed. This is what was expalined by Merlin and that is why the BCM600 unit has a shunt rated at 500amps. Hope this helps (and also hope it is true !)
 
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My understanding of this unit is that the shunt is rated at 100amps. It is possible that if your wiring configuration is set up such that you can start the engine from the domestic battery (which arguanbly it should be) then the shunt will be exposed to a larger current draw than that for which it is designed. This is what was expalined by Merlin and that is why the BCM600 unit has a shunt rated at 500amps. Hope this helps (and also hope it is true !)

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Yes - it is a 100 amp continuous rating. And yes I have started the engine using it, forgetting to change the 1, 2 both switch over, but it has not caused a problem. I almost always start using both batteries position, and no problems yet! From cold, I always use the engine battery.....

What is the draw from a starter motor (VP 2003T)?
 
I'm sure it is all true.

As far as I can tell, my starting battery is completely separate to the service battery. So no risk of flattening it accidentally.
 
Stephen,
I have the DCM600. It has the ability to measure 3 inputs, i.e. House, Start and Aux batteries.
The Aux can be used to measure bilge pump activity with a bit of messing about. I have an old Volvo hour meter for that.
The DCM600 goes into the theory a bit more to set it up. You have to calculate (they give you the instructions) values for Peukerts constant, which is relates to battery type and age for discharge rates, although you can use their recommended one.
It is sensitive enough to tell me when my little Rutland 503 awakens, down to 0.1 amps charge.
I have found it works extremely well, but it is a small display, and I prefer the NASA one.

Here is the feature list for DCM:

The 600-DCM3.2 Battery Monitor offers the following features:
§ 1/10th of an Amp resolution in the range of +/- 0-50A
§ The Matrix Monitors use a dot Matrix LCD allowing for Full screen information on Function selected.
§ Voltage monitoring for up to 3 battery banks.
§ 12 custom selectable legends eg: Start Battery, House Battery etc.
§ Hi/Low voltage alarm on all 3 banks.
§ Amps charge and discharge on house bank only.
§ Meter supplied with a 450-50mV shunt.
§ Capacity remaining in amp hours and percentage.
§ Software utilises Peukert’s exponent.
§ Suitable for use on battery banks 60-3000 Amp hours.
§ Low amp hour alarm.
§ New additional function for 2004
§ The bilge monitor function monitors bilge pump functions 24 hours, 7 days a week. Stores bilge pump
operations and accumulated time. Resetable when leaving the boat.
§ Function only available when third voltmeter position is not used.
The 600-DCM3.2 is designed to be surface mounted or recessed into a 2.5mm panel

Worth the money, no doubt at all.
 
Any battery monitor that uses a shunt to measure Amps in and out cannot give you a true reading of remaining battery capacity.
If you want to know how many amps you are charging at or how much you are discharging at then they will do that job.
If however you want to know what percentage is left in the battery then for me there is really only one choice
http://www.smartgauge.co.uk

OOps caught by quick post should have been in reply to Galadriel
 
I fitted a NASA battery moniter on a Contessa 32.

Found it very easy to fit, Very easy to set up and it has now been working fine since it was fitted several months ago.

The only comment I would make is that I think the short lead supplied to go from the neg battery lead to the shunt is a bit tender and should really be of much thicker wire. Other than that it is fine.

Iain
 
Thanks all. I think for what I want the NASA will do the job. its certainy going to be 100% better than what I have now, nothing. After doing research, I suspect that the other options suggested are going to be a bit more than I need.

My main concern has been, will the NASA meter work OK, after all it is cheap compared to other options, but then its not as feature full. As there has been no negative replies I take it that it will.
 
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Any battery monitor that uses a shunt to measure Amps in and out cannot give you a true reading of remaining battery capacity.

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That may be true for a system that just measures only amps with a shunt. According to the handbook, the NASA BM1 measures volts AND amps, and calculates the capacity taking account of Peukert's equation (whatever that is!), battery temperature, and charge efficiency. If Cervinia really thinks that fewer measurements makes for more accurate estimates, then I think he must be a salesman!
I think the BM1 is terrific, and I wouldn't be without mine.
 
OK Ill give you some examples where any shunt meter will read wrongly

1:
My navigation batteries have been sitting unused in the boat for a couple of months they have self discharged as all batteries do and are now about 89%. now nothing has gone out or in through the shunt so the meter wil still read 100%.

2:
Batteries are a couple of years old when new they had a capacity of 200Ah and I used to discharge them by 100Ah down to 50% as measured on the meter.
Now as with all batteries the capacity has dropped say to 160Ah but I have no way of knowing this as the meter will not tell me.
So I still discharge by 100Ah and the meter tells me 50% except that its not its discharged by 60% as the capacity is less.
So in both cases the meter is not telling the truth.
I could go on but wont.
 
1. "My navigation batteries have been sitting unused in the boat for a couple of months they have self discharged as all batteries do and are now about 89%. now nothing has gone out or in through the shunt so the meter wil still read 100%."

................doesn't seem to be so with my Nasa BM1. Voltage will drop during self-discharge and whatever the BM1 does presumably takes account of it, and the charge % certainly drops on my boat when not in use.

2: "Batteries are a couple of years old when new they had a capacity of 200Ah and I used to discharge them by 100Ah down to 50% as measured on the meter.
Now as with all batteries the capacity has dropped say to 160Ah but I have no way of knowing this as the meter will not tell me.
So I still discharge by 100Ah and the meter tells me 50% except that its not its discharged by 60% as the capacity is less."

............fair enough, but as you can guess what the capacity has fallen to, you reprogram the BM1 with the new capacity.
I think it's a good, low-cost monitor, does the job for me.


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Didnt know that it managed to deal with self discharge thats good that it does.

Not sure how you would guess the reduction in capacity, apart from the fact that the period that the equipment runs for would diminish, so despite having been involved in electrical systems for years I wouldnt like to try and make an accurate guess.

On our two boats the systems are very different, the livaboard has complex systems on 12/24 and 230v.
The sailing boat has virtually none just a 1,2,both switch and no monitoing but then apart from navigation equipment and lights there isnt any other electrical stuff.
 
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Not sure how you would guess the reduction in capacity, apart from the fact that the period that the equipment runs for would diminish, so despite having been involved in electrical systems for years I wouldnt like to try and make an accurate guess.

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The battery rest voltage gives a reasonable indication of %age capacity so, knowing that together with the Ah used to reach that point from fully charged, a reasonably accurate estimate of effective battery capacity should be possible. FWIW I rarely use the BM1's Ah display (other than for just this) since I find the simultaneous display of V and A generally much more useful.
 
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