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Old 25-06-2011, 18:57   #1
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Battery, alternator, shut question

The system on our boat is pretty simple. No AC power, no solar, no wind, nothing. Just the Alternator (Balmar) , battery switch, 2 battery banks (1 2 6v rolls 262 in the house bank, and 1 12v agm starting battery)

I was wondering why there is a shunt (400 amp) in line between the alternator (balmar) and the battery switch?

No problem. Everything works great. Just wondering why the shunt is there. Just trying to learn everything I can about all the systems on the boat.
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Old 25-06-2011, 19:03   #2
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Re: Battery, alternator, shut question

Shunts are used to measure current flow. Especially high amounts of current flow. Connecting a milliamp meter guage to the two sides of the shunt enables a proportional measurement that can be calibrated and displayed as current/amperes.
- - So most probably sometime in the past an ampmeter was attached to the shunt to measure the current flow from the alternator. If there are two skinny thin wires attached to the two head blocks of the shunt follow them and see where they go. You might find an ampmeter at the ends of the skinny little wires.
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Old 25-06-2011, 20:14   #3
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Re: Battery, alternator, shut question

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...Connecting a milliamp meter guage to the two sides of the shunt...
You would connect a millivolt volt meter across the shunt, not a milliamp meter. The rating should be stamped on the shunt, but shunts are often calibrated to produce a 50 mV voltage drop at rated current - in this case at 400 amps.
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Old 25-06-2011, 21:00   #4
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Re: Battery, alternator, shut question

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Originally Posted by phantomracer View Post
I was wondering why there is a shunt (400 amp) in line between the alternator (balmar) and the battery switch?
Typically, shunts are connected to the negative battery cable right at the battery.

Are there any small wires connected to the shunt?
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Old 26-06-2011, 02:25   #5
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Re: Battery, alternator, shut question

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You would connect a millivolt volt meter across the shunt, not a milliamp meter. The rating should be stamped on the shunt, but shunts are often calibrated to produce a 50 mV voltage drop at rated current - in this case at 400 amps.
You can do it either way. Blue Seas uses a high resistance measuring device, voltmeter, where the shunt carries nearly the entire current.

Stewart Warner uses a low resistance measuring device, ammeter, where the current is divided in some fraction.

Troubleshooting my friend's boat, I said here's your problem, the voltmeter has a short, having come across that style of shunt meter before. Going to the store I noticed on the box that the replacement gage was an ammeter, OK start over. Discovered that the heat shrunk, adhesive lined crimp connectors to the ammeter that had been put in less than a year before already had corrosion. There was nothing wrong with the gage. It worked out to be a 6:1 ratio of current in the shunt to meter.

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Old 26-06-2011, 05:10   #6
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Re: Battery, alternator, shut question

Thanks..there are no wires, other than the big battery cables attached.

So there is no impact on function.

There is an amp meter on the bulkhead, but there are no wires from this shunt, uless there is another shunt somewhere else.

here is a pic of it
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Old 26-06-2011, 05:47   #7
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Re: Battery, alternator, shut question

PhantomRacer,

The two small screws are where the ammeter leads would be attached if it was connected. It was probabley used in the past to measure current output from the alternator.
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Old 26-06-2011, 06:41   #8
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Re: Battery, alternator, shut question

I installed ammeter on both my alternators so I can see what is going on with the charging from each. Looking at the shunt, I suspect it would work with a blueseas meter. I would suggest a meter a bit larger than the charging capacity of your alternator. Looks like a balmar regulator. I also connected up warning lights for over heat alternator or battery. You can also add switch to half the alternator output in emergency situations. Good gear ...
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Old 26-06-2011, 14:33   #9
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Re: Battery, alternator, shut question

Quote:
Originally Posted by Adamante View Post
You would connect a millivolt volt meter across the shunt, not a milliamp meter. The rating should be stamped on the shunt, but shunts are often calibrated to produce a 50 mV voltage drop at rated current - in this case at 400 amps.
Your're quite right, got my "milli's" backwards.
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Old 26-06-2011, 19:38   #10
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Re: Battery, alternator, shut question

Sounds great! I wasn't sure if the previous owner installed it for another reason.

The Balmar works great. Like it a lot. Til the regulator failed a couple years ago. Balmar send me another at reduced cost.. They do have a dump regulator, that a rep gave me at a show, to use in an emergency if the regular one fails (I complained that I thougth balmar should have given me a new one, only used one season, but was a few years old). Great techs there. I was impressed with their service (even though I didn't get a free replacement)

THe regulator is nice, it scrolls through the programs, showing what the output is being measured at, what the battery level is at, etc. Neat stuff. Wife wants to know what is so interesting when I have my head poked in the engine room looking at the regular
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