Two shunts connected to one Ammeter

[tdalke]

Hey guys, just looking to find out if it's okay to wire multiple shunts to one ammeter gauge? I have an existing shunt and ammeter, but I'd like to be able to see how much juice our SSB radio is using. So instead of running 4 awg the 20' to our existing shunt it'd be nice to be able to place another shunt closer to the SSB battery connection and run 16awg the 20' to our existing gauge. This okay?

[Matt Johnson]

Yes. We did it before with a dpdt switch connecting one ammeter to a shunt with two sides. Each sides sense wires are all that are sent to the switch.

Oh, one other thing. Digital ammeters sometimes don't like the switching. Try yours first by disconnecting the sense and then reconnecting to see what the display does.

Matt

Sent from my LG-V410 using Cruisers Sailing Forum mobile app

[Frankly]

If you install a switch (DPDT) at the meter, then you will be able to read the current at both locations. A SSB transmitter current draw varies significantly as you talk or send a Pactor message. Not sure that you will be able to make any sense out of the meter reading, particularly if it is a digital meter (as most are).

Even if the run is significant, probably don't need any large cable as the meter current draw is typically rather small (so small voltage drop).

[Pete7]

Sterling have a battery monitor device that can have up to 4 shunts attached and by selecting the right button on the front of the device it will show instantly what that shunt is doing. I did have two shunts on mine but took one out to simplify the system.

Oh, just seen how much these things are, I paid a third of this:

Power Management Panel | Sterling Power Products

[StuM]

How long do you need to monitor it for? I'd just use clamp ammeter to see what it draws.

[tdalke]

Originally Posted by StuM

How long do you need to monitor it for? I'd just use clamp ammeter to see what it draws.

I have a few electrical appliances I'd like to monitor at will, and a clamp would be great but I'm afraid I can't get to the wires very easily.

[tdalke]

Thank you guys for the replies! I'll look into a couple of the options posted, especially the DTDP switch.

[noelex 77]

As others have suggested what you are proposing is fine. However, it will not work if it is a battery monitor, it has to be just an ammeter.

If you are going to the trouble of installing a second shunt, switch and wiring the other option is a second ammeter. These days they are not expensive. You can get a brand name marine unit like this Blue Sea model for about $60 and that includes the shunt.

The other option is an eBay ammeter that will much cheaper again. These can be OK, but it is more difficult to pick a unit that will be reliable.

[bletso]

Wire length should be unimportant as the shunt carries the current and you are really measuring a voltage across the shunt which represents the current through shunt.

[boatbod]

The two essential elements will be twisted pair wire and a DPDT switch to alternate between the two sets of shunt wires. Twisting the wires prevents EMI and inaccurate shunt readings.

[seabreez]

Originally Posted by StuM

How long do you need to monitor it for? I'd just use clamp ammeter to see what it draws.

Does an amp probe work on direct current?

[Bor the Wolf]

The problem with multiple shunts in parallel is that you also get multiple ground levels. That may not be a problem but it is a huge problem if the equipment is interconnected as is often the case with modern multi function displays. (NMEA0813, NMEA 2000, etc.)

I got myself one of those el cheapo clamp meters like the UNI-T UT203. This device allows me to measure any current draw by clamping the meter around the power wire of the device. Often we measure for a limited period after which we know the average current draw of a device and there is no longer a reason to measure it.

Another method is by using the battery monitor. It shows me the total current draw from the battery. By switching a device on and off I can see the difference in current draw on the battery monitor. The current difference is what that particular device is using.

But maybe it is my mindset? I am only interested in battery management and hence the total current draw from the battery. From most devices I know the average current draw. (There is a list on one of the back pages of the ships log). And those average current draws are all I need to do my calculations and manage the battery.

[canyonbat]

Originally Posted by seabreez

Does an amp probe work on direct current?

Yes, we used to use DC amprobes to calibrate DC welders.

[S/V Alchemy]

Originally Posted by Pete7

Sterling have a battery monitor device that can have up to 4 shunts attached and by selecting the right button on the front of the device it will show instantly what that shunt is doing. I did have two shunts on mine but took one out to simplify the system.

Oh, just seen how much these things are, I paid a third of this:

Power Management Panel | Sterling Power Products

The Bogart Pentametric does this too, I believe.

[Moontide]

Another way of doing things. I have a Mastervolt moniter that was on the boat when I bought it. At the time I was mainly interested in monitering the net amps going in/out of the batteries so the solar is connected upstream from the shunt. Works fine as if I want to know the solar output I can pull up the controller on my computer (Morningstar that has an ethernet connection so I can pull up current and historical information through a windows program).

I've decided I would like to also know the current drain without pulling up the solar program on the computer. Bought a cheap (read Chinese) meter with shunt.
Since there is no free lunch, the down side of the cheapness is that it can only handle 50 amps of load Not sure what the starters use, but the solar can kick out more than 50 amps and the inverter uses up to 90 amps when running the coffee maker. I know the draw of the coffee maker (uses 8 ah to make a pot of coffee).

Solution was to connect the negative side as follows:

Battery
Mastervolt shunt
On the upstream side of the shunt I have the negative from the inverter, negative from solar and one side of the small shunt.
Small shunt
On the upstream side of the small shunt I have the negative from the other loads.

Not necessarily a total "yachtsman" solution, but provides the info I want without having to fire up the computer and do (simple) math.
Bill
Wired it in series with the negative from the controller