Which Battery Monitor?

[EdEssery]

I want to get a better understanding of power consumption and charging on my boat. I'm therefore planning to install a Battery Monitor.

The boat has a domestic bank of two 110AH batteries and a separate engine start battery.

I am leaning toward spending about £90 on a NASA BM-1.

Before I do this, can anybody suggest why I should consider the alternatives (e.g. Victron BMV-501, BEP DCM600, Xantrex Link 10 etc.) all of which seem to do much the same thing in the same way but at twice the price or more of the NASA unit.

I know some support multiple battery banks - I don't need this as I only want to monitor the domestic bank.

Thanks,

Ed

 

[Conachair]

Never used a nasa unit so can't comment there I'm afraid, I do however have a BEP 600dcm which works fine, as well as domestic bank voltage/amps you can either watch voltage on 2 different batteries of voltage of one battery and time the bilge pump has been running. Think mine was about 100 quid at boat show a few years ago.

 

[roly_voya]

I could not see much difference between makes when I selected mine (Sterling pawer management) so it came down to what you wanted to monitor. I wanted to 'see' 3 battery banks (domestic, engine & electronics) plus alternator output so needed 4 chanels and the Sterling is the only one that allows that. The other factor is power draw, the BM1 only reads up to 100a and I needed 200+ for the inverter. Very pleased with the unit and find the simultainious display of volts and amps very useful. Only word of caution is that I had not realised how big the shunts are and had problems finding suitable locations. The BM1 shunts are much lower power so might be smaller but check!

Other useful thing was to get a plug in power monitor, £10 from Maplin, and run the inverter output through it. Alows easy isolation of the units output and monitors V,A,Watts, Hz plus total Kw hours. Very useful and £300+ to do the same thing with a BEP monitor.

 

[MatthewCoyne]

As in previous post, providing you need only monitor 1 bank of batteries and max load never exceeds 100A then the Nasa unit is great.
I have one myself on my Quarter Tonner and it is a real bonus knowing when the lights are gonna go out !

 

[john_morris_uk]

We have Sterling Power Monitor. Does whats its says, and the only annoying habit is for the instrument to indicate very low (200 milliamp) currents when I KNOW that the current is zero! Howevere in the grand scheme of things, it doesn't matter and I ignore it.

What it does do very well is measure how many amp-hours you have used, and then allows for the losses in the charge discharge cycle in calculating how much charge you've actually put back in.

 

[whipper_snapper]

Can the shunt be connected so that it 'sees' the voltage drop on engine start? ie, the current for the starter motor is flowing though the shunt ? I imagine this could exceed 100A. I assume that would not be a problem provided the shunt could handle the current and the instrument could handle the large V that would appear on the shunt?

 

[Phoenix of Hamble]

Ed, I've got the Nasa unit, bought it 12mths ago.... and its been excellent.... I wish i'd bought one years ago... it makes power management much easier... can't see any sense in your situation in spending double the money on anything else.... save the extra for another boating goody!

 

[Jonny_H]

We got the BEP600 unit - the shunt is 400A, vs the 100A for the Nasa. As this goes to the domestic battery bank I know I am very unlikely to ever get near 100A, however, if my engine battery died and I had to start off the domestic batteries this could pull more than 100A ... the shunt wouldn't like that.

This was the rationale I fell for anyway (thanks to the sales guys at Merlin). BEP seems very well made, smaller and neater than the Nasa unit, and comes with a good manual etc. My only critiscm of the BEP is that you need to buy the wiring harness seperately (which is a multicore twisted pair cable), again, Merlin say this is so you get the right length and don't have lots of spare cable or need to sacrifice location due to the cable being too short.

BEP ones are £169 from Merlin at the moment - but cheaper at the boat shows if your prepared to wait until Sept!

Jonny

 

[whipper_snapper]

[ QUOTE ]
however, if my engine battery died and I had to start off the domestic batteries this could pull more than 100A ... the shunt wouldn't like that.

[/ QUOTE ]

That was the question I asked above. What do you mean by 'wouldn't like it'? I would be suspired if it failed or significantly limited the current - a shunt is just a low resistance designed to drop a known voltage for a known current. My best guess is simply that it would drop an offscale voltage, But I would like an authoritative opinion as I have a single bank for domestics and engine.

 

[Phoenix of Hamble]

Nasa have previously stated that the 100A is a continuous rating, and it is OK for upto 400A for short periods.....

 

[whipper_snapper]

Thanks, looks like it may be an issue after all. Any idea what current cranking a cold 10Hp Yanmar would pull ?

 

[Anwen]

The cable for the BEP unit is essentially microphone cable - I bought mine from Maplins at much less than the Merlin price. And yes, it is tinned.

 

[alan]

I second the BEP600; you can also get a version which has water/waste tank monitoring as well (you need the appropriate sensors in addition). Costs a bit more but as I didn't have any tank level monitoring so I went for it!!

Alan.

 

[Jonny_H]

Wish I had known that at the time. The Merlin cable is quite confusing as it a series of twisted pairs, white & black (twisted), red & black (twisted), blue & black (twisted), green and black (twisted) and a shield. I didn't realise this at first and stripped them all back, connected white, blue, green, red, black and shield .... went to the other end and thought ... now which of the 4 blacks did I use??!!

Anyway - lesson learnt ... think first next time!!

Jonny

 

[Jonny_H]

I think they do a whole series, DC monitor, AC monitor, Tank monitors, and as you say a combined DC/Tank one and a combined DC/AC one.

All look very smart - I have bought a fair bit of BEP stuff (fuses, switch panels, battery switches, VSR) - not the cheapest stuff out there, but definately qaulity stuff.

Jonny

 

[alan]

Agree. I bought the BEP600 as part of circuit breaker panel. Looks reall good with backlighting e.t.c.

As you say: it costs, but the quality is excellent.
Alan.

 

[charles_reed]

The Yanmar GM

starter is 2.5kW for the 1GM and 3.5kW for the 2/3GM.

 

[Phoenix of Hamble]

Re: The Yanmar GM

so thats a max of about 200Amps

 

[wiggy]

Re: The Yanmar GM

I have NASA with 1GM10 and have had no probs with occasional use of domestics to start engine through shunt, its a great bit of kit.

 

[whipper_snapper]

Re: The Yanmar GM

OK, thanks. I will go with the BM-1 and wire it so that the shunt is bypassed by the starter motor. I guess that means the AH counter will be out slightly, but that's no big deal.