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Old 18-06-2010, 03:09   #1
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Amp Metre

Can someone tell me how to connect an amp metre into my boats electical system.

Maybe I should add, Im not totaly incompitant but my understanding of electronics and the terminolagy is limited.

I am rebuilding a 42' cruising catemeran that has been totaly neglected on the water for at least 12 years, I have done ALL the work myself, both for budget and I have not found anyone in my area who is capable of doing a half decent job.
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Old 18-06-2010, 03:29   #2
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Barry, are we talking just an ammeter or do you want something to do a bit more and count amp hours?

The US folk seem to like "link systems", this side of the pond "Sterling" are popular. You need a shunt installed, normally in the positive battery cables and the meter then measures the amps and keeps a count of in and out.

Have a read of this, although they all work on a similar theme.

Sterling Power Products: Power Management Panel
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Old 18-06-2010, 04:53   #3
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Thanks Pete

I am looking at amp metre only, I already have the metre.

I am keeping the boat with the bare minimum. It is comfortable and sails well and with my gadgetry incompitence I realy dont want to go back to school at this stage.

Barry
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Old 18-06-2010, 04:59   #4
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Depends what you want to measure. If you just want to measure charging amps, i.e., amps going into the battery, you can put an ammeter in the positive lead to the battery. If you're going to measure a significant amount of current, you'll need a shunt....a device which can pass a lot of current with low resistance and which has a little tap for connection of an ammeter.

BTW, it's not a good idea IMHO to use older car-type ammeters. They have small terminals which are unsuited to the high amperages found on many cruising boats and are not particularly accurate or robust. Much better to use an ammeter with a shunt, designed to measure high amperages. These meters can be mounted quite a ways away from the shunt...anywhere you want them.

I have such an arrangement on my boat; the ammeter is set up to measure how many amps are being put into the batteries by the engine alternator.

By contrast, most battery monitor devices like the Link series, the new Victron, etc., are installed in the negative lead to the battery. They can measure the amount of amps into or out of the battery bank, as well as voltage, amp-hours remaining, etc.

Bill
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Old 18-06-2010, 05:09   #5
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amp metre

Hi Pete,

I am gathering from your reply that I need to get a shunt, how do I calculate what shunt to get? and that then goes inline on the posative battery cable?

Barry
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Old 18-06-2010, 05:18   #6
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amp metre

Thanks Bill,

I hadnt conciddered the amps going into the battery, but I like it, this is starting to erode into my keep it simple theory but not too badly.

The reason I wanted an amp metre was for an indication that something is switched on or how much is on.

Barry
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Old 18-06-2010, 05:59   #7
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Thanks Bill,

I hadnt conciddered the amps going into the battery, but I like it, this is starting to erode into my keep it simple theory but not too badly.

The reason I wanted an amp metre was for an indication that something is switched on or how much is on.

Barry
Barry,

Sounds to me like you better rob your piggy bank and buy a proper battery monitor, then. Look at the new Victron...the smaller of two models they make. It's under $200 here in the States, and is very good quality equipment (like everything Victron makes).

Here's a link: Victron BMV 600 Battery Monitor

Bill
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Old 18-06-2010, 06:19   #8
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Barry, presumably you are starting from scratch if your are rebuilding this boat. If I were you I would consider one of the more modern amp hour counter systems, because it will tell you not only how many amps you are using, or charging, but the cumulative totals.

So if you have been anchored out overnight using lights, fridge and radio etc, you can see how long to run the engine or how long solar will take to replace those amp hours. It will also give you a good idea how many amps you have taken out of the batteries so stops you depleating them too much.

I fitted the Sterling one in the spring so it came with the correctly sized shunt. It was just a case using the existing cables for one side of the shunt and some new short ones from the other side to the batteries. We now know exactly how much we have used, however in the past we had to guess how much a fridge used over night and run the engine for a few hours hoping we had put enough back into the bank for the that evening.

After a recent night on board we needed to replace about 45 amp hours. The battery monitor showed the 2 hours of motoring the following day didn't replace enough and we were still something like 26 amps (12%) short. Wasn't a problem and the solar panel made up the difference over the next week, but we wouldn't have known that from just an ammeter.

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Old 18-06-2010, 06:52   #9
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When I rebuilt the electrical system on my boat a few years ago I replaced all the meters. It included amp meters on both the AC and DC. Even though the AC meter was new and rated at 50 amps to my surprize it does not work possibly received that way. The DC amp meters works just fine. Don't remember rating as I write this. Anyway, the amp meter needs to be in series with all electrical loads to register. You do not need a shunt if meter is designed to handle amp loads.
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Old 18-06-2010, 07:30   #10
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amp metre

Thanks S/V Surya,

do you use a intergrated system or just individual metres?

Barry
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Old 18-06-2010, 07:36   #11
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Hi Pete,

I am gathering from your reply that I need to get a shunt, how do I calculate what shunt to get? battery cable?

Barry
Hi Barry some cheap ammeters have a shunt in them. So before going and buying one (and they can be expensive!) lets have a look at yours.

Can you post a photo here?

Or take yours apart and look in the back. If theres a thickish bare wire in the thats the shunt.


Mine cost about $10 and the shunt was inside. Is 20amps I think and has been fine working with my solar panels.

I can't find a photo on the internet of what I mean... but the shunt is in the back of the ammeter if it has one.


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Old 18-06-2010, 07:43   #12
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amp metre

Hi Pete,

I am starting from scratch but not by choice. I wanted to just do the basics and go sailing but the deeper I looked the more junk I removed until I realised that I had totaly gutted it and the other realisation was that I paid too much and Im getting into things a little over my head. My problem at the moment is I am trying to progress faster than I can digest all the info I am needing, not only in the electrics but everything!

I WILL FINISH THE JOB (I need to keep teling myself that)

Barry
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Old 18-06-2010, 08:20   #13
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Thanks S/V Surya,

do you use a intergrated system or just individual metres?

Barry
I have individual meters. When I rebuilt the panel I removed it from boat and did installation at home but could have been done on board. I cleaned up all electrical connections and tested breakers. To make sure meters fit I replaced same part numbers.
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Old 18-06-2010, 09:41   #14
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Thanks Mark,

Il check that.

Barry
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Old 18-04-2011, 20:53   #15
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Re: Amp Metre

I am trying to decide between the Victron BMV 600 and the 602. The house bank and my starter bank are 15 ft apart from each other I am wondering if I will be able to use the 602 to monitor batteries that are so far from each other. If not then I will settle to just monitor the house bank.
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