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Go Back   SailNet Community > General Interest Forums > Gear & Maintenance
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  #1  
Old 06-07-2011
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Shunt for panel ammeter?

I am rewiring my main house panel:



and the load ammeter ("LOAD AMPS") was not hooked up when I bought the boat.

I assume that it needs a shunt of some sort, to be connected inline in the ground lead to the house battery bank, but can't find any definitive guidance by searching.

Can anyone point me in the right direction? Thanks.
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Old 06-07-2011
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If the ammeter was never hooked up, I doubt you have the required shunt...but look for it anyway between the battery and negative buss. I'm guessing you'll get your answer from "Westerly" or from Welcome to EmproShunts™.

Sorry, as I'm not an electrical expert in any way (also not connected to either business), this is the best I could come up with.

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Old 06-07-2011
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Some ammeters (especially the lower range ones) have the shunt built in, not separate. I would suspect the 30 amp range of yours would mean it has an internal shunt. External shunts are typically designed to have a 50 or 100 mv voltage drop across them at 100% rated current. If you need one, it will have to match the meter.
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Old 06-07-2011
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I'd vote with Jims, odds are the shunt is built in. But "odds" is still gambling, better to check with the maker. If you can't get any information...you can test it with some caution, i.e. connect a AA cell across the leads. If the meter barely twitches, it is reading amos directly from a built-in shunt. If it is designed to work with a shunt, it should misread the battery's available power (maybe 1600mA) as being a large voltage drop ona shunt, and show a 10A or way higher reading.
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Old 06-08-2011
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OK, I dug around in the box of misc. parts and bits that came with the boat and found what appears to be the shunt:





Per my understanding, this is then connected inline in the ground connection from the panel to the battery, and the meter is connected across the shunt, one lead to each side. I.e.


Code:
  
BATTERY NEG ----- SHUNT ----- PANEL GROUND BUS
              |           |
              --- METER ---
Right?
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Old 06-08-2011
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One more question... I have a separate monitor for the house bank, so I'd like to use the panel meters to indicate the condition of the starter battery. That would mean connecting the shunt to the starter battery side of the circuit in some fashion, however obviously it couldn't go inline between the starter battery negative terminal and the engine block as it couldn't handle the current of the starter motor.

There is a negative lead from the engine panel to the starter block that looks to be AWG 10 (2.5mm), so I'm thinking that connecting the shunt inline to that ground wire should indicate load/charging of the starter circuit, right? Or should the shut be inline in the ground wire from the alternator?
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Old 06-09-2011
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That sure looks like the shunt and your connection diagram is correct.

I don't think you can use this meter to measure the current when starting the engine. It will be far more than 30 amps.
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Old 06-09-2011
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JimsCal is right. If this circuit is also your starting circuit, you need to wire in a solenoid rated to the current of your starting motor (and then some).

Wire it in parallel to the shunt with the signal line wired to your starting motor energizing line.

I know Blue Sea systems sells such a solenoid, 500-700 Amps rated, or something like that. I have one. I have an ammeter wired in to the starting battery so I can see how much it's charging, so I use this solenoid setup to avoid starting current from blowing up my shunt. No problems in 3 years since I wired it up.
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Old 06-09-2011
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The analog amp guage on my boat is wired to the + side of the batteries then to the + side of the breakers. Also it doesn't use a shunt per sey it uses a heavy guage coil wrapped a few turns around a needle actuater.

Mitch
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