amp metre

bootsy

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I would like to fit an amp metre to calculate the amp thats going in and out of my battery bank. I have 12volt system running through a 1/2 both switch. Any ideas would be appreciated.
 

VMALLOWS

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There are quite a few commercial products on the market to do this, and I'm sure you will get numerous replies. They're mostly in the £150-£250 range.

I looked into making one myself a few years back but never came up with a circuit that attracted me. (these days likely to be microprocessor based, though it can be done with discretes).

If anyone has a circuit they can recommend, please comment. I only want the basic amps-in minus amps-out function, not any fancy battery management
 
G

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Now this may be a daft idea .......

Some battery chargers use a meter with the output lead wound around the external case .... the field set up is then proportional to the ampage ....... wouldn't it be possible to do similar, albeit keeping in the general course of cables etc. - so not being suitable to mount meter remote .....

But it would remove the need for shunts / resistors or anything else to reduce the load through the meter and wouldn't detract from the charge rate ?????

Nigel ...
Bilge Keelers get up further ! I only came - cos they said there was FREE Guinness !
 

VMALLOWS

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Yes, you can certainly measure current with a 'clamp-around' device (or wire wrapped around the cable), but feel doubtful you could effectively cover the current range (from a few mA to several hundred amps.) with only one transducer. Maybe someone knows better? Anyway, you still need the electronics to do the add/subtract for the amphours-in /out.
 

tome

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I also looked into this, but battery charge/discharge algorithms are a little complex unless you are draining at a rate which will give exactly a 20 hour discharge. Also, you need a low resistance shunt which can handle a lot of power to measure the current in and out.

In the end I fitted a Link 20 unit which I must say is absolutely brilliant IMHO, though it cost over 200 quid. This uses a micro and measures amps in and out, calculates ampere hours used or remaining, and indicates time until charge required based on what is switched on at any one time. Takes out all the guesswork so you only charge when you need to. You program it with the ampere-hour rating of each bank. Since the starting battery isn't of much interest I'd probably go for the cheaper Link 10 single bank unit.

It has a lot of extra uses - eg I can see whether a circuit is working (eg tricolour) by watching the increase in current consumption, and can monitor the charge rates into each bank from my mains charger when alongside.
 

TonyMS

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You can do it for around £40 from RS - http://www.rswww.com. There are centre zero meters, eg 196-8418, and shunts, eg 257-363.

I did this some years' ago, with an earlier meter and winding my own shunt simply by coiling high resistance wire across the terminals. Was still working when I sold the boat 10 years later, despite location where there where leaks.

Have fun

Tony
 

Chris_Jam

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I could do with a bit of that as well - if you could pass on a list of parts and fitting instructions, that would be great. I boat on a small buget and the cost of battery management systems would leave me broke!

regards
CJ
 

rex

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I am not sure what you have now but a digital volt meter will give a good idea of the state of charge. You can get one that just plugs into a cigarette lighter socket for about ten pounds if installation is a problem.
 

muchy_

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Connect it like this...

On the back of the ampmetre there are two big terminals. You take you alternator output to one terminal and the other terminal goes to where ever that cable goes now. In other words it's just fitted in-line on the alternator out put cable.
 

TonyMS

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You realise that I'm just an amateur hacker - not the right bloke for detailed intructions!

However:

1 Decide what are the max amps you'll ever need to measure and select the appropriate shunt. Eg for 10A select 257 -363

2 Select the meter with the appropriate Full Scale Deflection, ie 196-8553 for 3A or 30A, or 196-8547 for 10A

3 Fix the shunt to the rear of the meter so that it shorts across the 2 terminals

4 Wire the meter into your circuit so that all the current goes through it.

Presumably you don't want to measure the starter current (typically > 100A), so don't run that through it. If you have separate engine and domestic batteries, a good solution is to put the meter between the battery negative terminal and its connecting wire.

Make sure you use wire heavy enough to carry the load. If you want the meter on a panel miles from the battery, that's a lot of thick wire. Alternatively, you can mount the shunt near the battery and have the meter wired in series with it, connected with light wire, and as remote as you like.

If all this is incomprehensible, you really need to find a mate locally who is sound on basic electrical circuits and can examine your setup and advise.

Best of luck!
 
G

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Don't mean to be picky but where you said

'Alternatively, you can mount the shunt near the battery and have the meter wired in series with it, connected with light wire, and as remote as you like.'

it should be in parallel not series so it doesn't interfere with the current.

Cheers

Derek
 
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