Shunt for panel ammeter?

[rhumbunctious]

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.

 

[Stu Jackson]

Usually in that range of amperage they are small enough to have internal shunts. Open up the panel and see what's in the guts of the ammeter. Only YOU can see behind there unless you send us pictures....

http://c34.org/bbs/index.php/topic,6032.0.html

Some ammeters like the one on your panel, can be connected to the positive side, although this one looks like it takes the alternator as plus (input) and the distribution panel (loads) as negative. Lots of the new battery monitors, which include ammeters, rae on the negative side, but they don't have to be, especially on a panel ammeter like yoursd which is right by ALL of the POSITIVE wiring, and little of any negatives.

 

[galeus]

Obversation-It is most likely that your alternator is rated higher than 30amps.

 

[William_H]

Ampmeter rating

Yes the alternator will be rated at more than 30 amps however I would not worry if I were you. It is unlikely you will get a + 30 amps into your batteries and if so not for very long. A charge controller may bring it closer to 30 amps for longer. I don't think the amp meter will be damaged by a short term small overload.

You need to find out if the amp meter is intended to have an internal or external shunt. A simple test might be to put a Digital volt meter on ohms across the terminals. A reading of 100 or more ohms means it is a sensitive moving coil meter intended for an external shunt. When you apply the DVM you may see the meter kick a little.
If the resistance measures very low and you get no meter kick then it has an internal shunt. This means that the high current wiring either +ve or -ve must be brought to the panel. It should be wired in series with either the battery negative or positive. It will then measure current into and out of your service battery (not the engine battery) unless you make it for engine battery only.

If you need an external shunt you need one that matches the meter. (for 30 amps)
There is nothing mysterious about a shunt. Any resistance will do however it must be precise to make the meter read 30 amps accurately. So the volt drop along a long negative or positive wire may be enough to make the meter indicate. But probably not sufficient deflection. You might need a piece of stainless steel about 20 gauge (1mm thick) 20 mm wide a strip about 50mm long with large holes near the ends to take the heavy wire lugs carrying the current. 2 more holes near the ends take lugs for the wire to go top the meter.
You will need another amp meter to fit temporarily in series so you can compare the actual current with what your meter reads. A 10 or 20 amp digital multimeter will give sufficient accuracy which can be interpolated for 30 amps. A longer strip of SS will in a linear fashion increase the meter reading while a shorter distance between the big lug holes will reduce the reading. In a similar way the distance apart of the 2 pick up holes will reduce the meter reading. The whole strip can be mounted on insulated plastic and mounted near the battery. If you fit it into the +ve line you should fit fuses to the wires going to the meter. You could calibrate the meter for 60 0 60 amps and remark the dial.
Or you can try to find the correct shunt and pay a fortune for it. good luck olewill

 

[SHUG]

To calculate the shunt resistance required you meed to know the current rating of the meter (possibly 100mA) and the resistance of the meter (Possibly 50ohms) You can use a multimeter and ingenuity to find these values.Then it is simple to calculate the resistance of the shunt to give the meter FSD at 30amps.

 

[VicS]

Then it is simple to calculate the resistance of the shunt

I suspect a significant number of the people who use these forums wont have the faintest idea how to do that !

Anyway I thought shunts were normally rated by X mV at Y amps eg 50mV at 100amps.

 

[pvb]

I wouldn't have thought a 30A ammeter would have an external shunt. However, most Westerly panels were supplied by KDD, whose owner posts on here as Halcyon. I'm sure he'd be pleased to help you if you either PM him or email him at KDD.

 

[philip_stevens]

However, most Westerly panels were supplied by KDD, whose owner posts on here as Halcyon. I'm sure he'd be pleased to help you if you either PM him or email him at KDD.

I've posted his details on the WOA site.

 

[rhumbunctious]

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.

BATTERY NEG ----- SHUNT ----- PANEL GROUND BUS
              |           |
              --- METER ---

Right?

 

[rhumbunctious]

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 shunt be inline in the ground wire from the alternator?

 

[steve28]

you would have to insert the shunt inbetween the alternator B+ and the battery, some outputs are joined to the starter feed on the starter solenoid. The main switch panel would then be fed from the other side of the shunt to give the discharge reading as well.


Steve