which battery monitor

[Amulet]

.... But first I must get the biggest battery I can afford and find space for

Mmm... Do remember that, no matter how huge your battery is, you still have to put everything you take out back in again. Size just gives you a bigger overdraft limit. With my set-up - two 110 amp hour, I can easily cruise for 4 days (fridge off) if I then get a charge in a marina. (My engine charging can only do 12 - 15 amps flat out, which ain't much use.)

 

[pvb]

If you have an inverter that might draw more than 100A, you might need a 200A shunt.

Ditto if you have an alternator and/or battery charger that charges at more than 100A.

Did you see the bit in the OP which said he had just one battery?

 

[Scorpiokent]

what is the best battery monitor to get for a 2 x 12v battery system (one start one domestic)

By best I mean economic as well Is that NASA BM thingy any good?

I have the BM2 which is the upgraded version of the BM1, checkout cheaperchandlery.com, cheapest I have found.

 

[Scorpiokent]

Get the BM2 nasa monitor, great kit cheap pricetag

Victron also makes a good, easy to install one. They have two models, one measures reserve bank voltage.

http://forums.catalina.sailboatowners.com/showthread.php?t=125606

Agree that monitoring a reserve bank is usually unnecessary.

Get the BM2 best price I have found is £111 at cheaperchandlery.com

 

[Richard10002]

Get the BM2 best price I have found is £111 at cheaperchandlery.com

Is that new or 2nd hand - the site seems to stress that it is cheap because it sources 2nd stuff...... But it also mentions new stuff in places.... A Bit confusing to be honest

 

[Richard10002]

Did you see the bit in the OP which said he had just one battery?

Yes but I'd forgotten

Having said that, I don't think it's a bad thing to cover all the bases, if only for future readers who might come across the thread in a search.

 

[pappaecho]

If you want cheap. O bought a backlit 12volt digital voltmeter for £1 from China with free postage. Mounted it in a little plastic box from Maplin, and bought a 3 way switch ( monitoring 3 banks) .

It is very good for £4 all up.

 

[Loggo]

I worked as a railway guard (later driver) on BR in the late 70's early 80's and was confident that I knew what a shunt was and how to do it. How does moving large coal wagons fit into an electrical scenario ?

Happily following this thread as I would also like to monitor consumption more closely, currently using a Chinese made jobby (as previously mentioned) that does the job with a noticable absence of trickery for about £2.50 - tested to be accurate to within 0.2 amp.

 

[pvb]

Happily following this thread as I would also like to monitor consumption more closely, currently using a Chinese made jobby (as previously mentioned) that does the job with a noticable absence of trickery for about £2.50 - tested to be accurate to within 0.2 amp.

It's all very well knowing what current is being drawn from, or put into, your batteries, but what you really need to know is the amp-hours data. This needs something rather more sophisticated, which is why battery monitors cost more than your Chinese jobby.

 

[PabloPicasso]

not all batt monitors have a shunt so what does the shunt do?

 

[VicS]

not all batt monitors have a shunt so what does the shunt do?

In the context of measuring current flow ( amps) the shunt is a resistance, a very low low value resistance but nevertheless a resistance.

The current you are wanting to measure flows through the shunt and produces a small voltage across the shunt which is directly proportional to the current.

The instrument, battery monitor, ammeter or whatever measures this voltage and displays it as the value of the current flowing through the shunt.


the shunt can be placed conveniently in the existing wiring without re-routing it to an instrument in the panel.
Since very little current flows through the wiring between the shunt and the instrument it can be light and can be lengthy without affecting the readings etc

Now awaiting the pedants to pick holes in that!


There may be a better explanation on the tb-training website

 

[Vara]

not all batt monitors have a shunt so what does the shunt do?

It allows you to measure amps, the primitive cheap, albeit accurate meters measure only volts.

Basically it gives a fuller picture of what's going on in your boat's electrical system.

And what Vic said

 

[cimo]

not all batt monitors have a shunt so what does the shunt do?

the shunt introduces a low resistance into the circuit. A small voltage drop develops across the shunt (mVolts) which is directly proportional to the current running in the circuit. The batt monitor uses this voltage drop to indirectly measure the current.

the alternative is to place the monitor in circuit. but this can become impractical for mounting purposes - as you would need to run the heavy cable to the mounting position and back.

postedit - gosh, you got to be quick here today! essentially what VicS and Vara have said.

 

[halcyon]

Now awaiting the pedants to pick holes in that!

Connection should be by a twisted pair, voltage and current are extremely low, so can be effected by other cables, giving false readings.

Brian

 

[Richard10002]

Get the BM2 best price I have found is £111 at cheaperchandlery.com

Ordered Thursday, arrived Friday. P & P about £3,

Definitely new.

 

[nigelmercier]

You want cheap, get Nafa. Otherwise, CruzPro.

 

[Scorpiokent]

Don't think you will be disappointed, mounted mine on the engine housing looks the business, did you get it from cheaperchandlery.com? Mine took a couple of days to come, have also bought a few s/h bits from them as well, really cheap postage costs.

 

[Richard10002]

Don't think you will be disappointed, mounted mine on the engine housing looks the business, did you get it from cheaperchandlery.com? Mine took a couple of days to come, have also bought a few s/h bits from them as well, really cheap postage costs.

Cheaperchandlery.com as per your recommend.

 

[Richard10002]

You want cheap, get Nafa. Otherwise, CruzPro.

Never heard of CruzPro. If I was going to spend more money, it would be Smartguage, Victron, etc..

The NASA BM models seem to get a good recommend. I probably wouldn't buy their navigation instruments.

 

[Zozo1202]

I have recently installed a Nasa BM-2. It seems working perfectly OK so far.

It was pretty straightforward to install although I'm happy I got the BM-2 with M8 screws on the shunt as it looks far more robust than the BM-1.

One question though. It seems the maximum Ah is supposed to be 600.
In fact I have two 700A.h batteries... Thus in theory (only) 1400 A.h. (it's a sailing boat, although nothing pulls out much, I like the idea of having a respectable autonomy).

Has anyone identified any reason why in theory the modules are limited to 600A.h ? Although I can integrate the flow of current OK, it wont let me go above the real capacities of the batteries.
Any idea welcome. Thanks