Wiring shunts and other stuff.

[roverhi]

Am redoing the wiring and trying to figure out how to handle shunts to get an accurate current draw measurement. Boat currently has two shunts connected together to handle the negative side of the wiring. The LinkPRO pulls off one of the shunts but have always suspected the meters accuracy. Have too many negative leads to use just one shunt. Is it critical how the two shunts are hooked together to get an accurate reading on the LinkPRO?? Would it be imperative to buy a junction fitting and run most of the wires there and then to the shunt?? Have the shunts to use as terminals and don't want to spend more money on the old girl to buy any more hardware unless I have to.

There is a black and a gray wire to connect to the LinkPro. Is the positioning of these leads critical?? In other words, does one lead need to go to the ground side of the shunt and the other to the boats negative connection side.

Do both the boats battery's negative leads have to go through the shunt or can one or both go directly to the engine block?? The boat's starter battery is about 6' away from the shunts and right next to the engine. Would be way shorter cable run to ground to the engine block rather than through the shunt. Only use the starter battery for starting unless the house bank totally fails.

[smac999]

you should have a single cable coming off the battery bank neg you want to monitor to the shunt. and from the shunt you can run negs around the boat. and to the batteries that are not going to get monitored. so normally the shunt is mounted next to the house battery and only the house is monitored. yes the shunt wires matter. otherwise the gauge will read backwards. -amps while charging and pos amps while draining. it is easy to check and reverse if needed.



unless you have the link 2000 you are only monitoring one bank and only want one bank to go through the shunt.

the link pro only does one bank and one shunt. so not sure why you have more then one. sounds like your wiring is a mess.

[exMaggieDrum]

I can't tell how you have wired all your battery cables on the negative side from your description, so this is just a couple of general thoughts. Most people want to measure the current in and out of the main house bank (regardless of how many batteries - assuming all in one bank). They do not measure the current in and out of the starter battery. The shunt has to be big enough to handle the max load at any time to avoid it acting like a bad fuse.

The house battery bank should only have one negative wire coming from it unless you have tried to use the battery post as a terminal strip - bad idea. If you must, install a (relatively inexpensive) single battery post stud and put all the negatives that go to the battery now on to it. Then install the shunt between the battery and this new post (with two cables). You can do this anywhere you can combine all your negatives to the one post.

If you want redundancy with meters you could install two shunts in series with the leads going to separate meters. If you want to measure the current to specific devices (alternators, inverter/chargers, inverters, chargers, solar, main panel, whatever), then you need to be able to isolate the negatives for that device to go to the battery. If any negatives go around the shunt, in whatever fashion, then you will not measure the juice that goes through there.

I am not a big fan of using the engine block as a main battery negative, but many boats are already wired that way. If yours is, then you can put the shunt in between that point and the main battery bank you want to measure current for. It is just like the separate battery stud terminal then.

[Stu Jackson]

Peter, I really don't know what you do or don't know about electricity. My initial and repeated reading of your OP seems to imply that wiring may not be your forte. It really does matter how the wires are run.

As Steady Hand has mentioned many times, these are offered in a friendly manner. If you alreay know this stuff, then ignore the links.

Ammeters & Shunts 101 Ammeters & Shunts 101


This explains how shunts for battery monitors need to be wired:

How to Wire a Battery Monitor by Maine Sail: Wiring & Installing A Battery Monitor - SailboatOwners.com

[DeepFrz]

Wiring should be something like this. You can use the bus bar or the PowerPost or both but all DC negative returns to the battery should go through the Shunt. Any current through a cable that bypasses the shunt will not be recorded on the battery monitor.

If you have two shunts in parallel then each shunt will only measure the current through it ignoring the current passing in the other parallel leg. I wouldn't think that having the shunts in series would be a problem. Some people add a shunt on the Pos. side of the battery to measure alternator output which effectively puts it in series with the Neg. shunt.

[Paul Elliott]

Originally Posted by DeepFrz

Some people add a shunt on the Pos. side of the battery to measure alternator output which effectively puts it in series with the Neg. shunt.

And this works as long as the Ammeter connected to this positive-lead shunt can deal with shunt voltages greater than +battery. Some can't, and require the shunt *only* be in the battery ground lead.

This is because the Ammeter (or monitor, etc) requires a power supply, usually the +battery and ground, and for many of these meters the shunt voltages must be less than the meter supply. Check the specs for the meter you would be using -- they should tell you.

[jeepbluetj]

If you are running more than one shunt, you can just use one if they're the same rating (mv per A). All a shunt does is converts current into a tiny voltage that then can be easily measured.

[roverhi]

Finally got all the wires labeled and moved all the fuses, shunt, bus bar and power post out where I can see them. They were high up inside a locker under the stbd. settee and hidden behind the batteries. Had to be a contortionist with your head upside down to see all the connections and then everything was blurry because I had to look through the tops of my bifocals. That was after removing both GC batteries just to get my head in the locker.

A few more questions on the shunt.:
1. The engine ground is led to the load side of the shunt. I thought that is what DeepFrz's illustration showed, but it may not, and thought I also saw that in one of Stu's Links. Somehow it doesn't seem right. Would think the engine ground would go on the battery side of the shunt. Which side does the engine ground wire go on??

2. Seems to me that with both start and house bank battery grounds (Negative) lead to the Battery Ground side of the shunt, the LinkPRO meter would read whatever battery bank is selected. Know that switching back and forth between house and start batteries would mess up any cumulative readings on the meter so the LinkPRO would have to be reset each time to get it to accurately show the history of that battery from then on. Seems like your suggestions that to get both batteries monitored I'd have to have two meters and two shunts would only be for constant simultaneous monitoring of both banks. Wouldn't that only be true for historical data and cumulative readings for each of the batteries??

3. The connection for the shunts is a 3/8" by 1/2" long bronze bolts. The bolts are too short to put more than two leads to a side. Can't find any 3/8" bronze/brass/copper bolts in Kona. Would it be a problem to use a 3/4" long stainless steel bolt if the 1/2" long bronze bolts prove too short?? Seems like that would work since the leads would be clamped to the Bronze/Brass/Copper chunk that makes up the body of the shunt.

Yes, when it comes to wiring theory I'm a dunce. Never got much beyond the garden hose analogy of how electricity works. Believe it or not, have wired three different boats that I've sailed from Coastal Atlantic, Coastal California, SoPac and Transpac without any problems. Of course they were simple set ups without any sophisticated electrickery thrown in. Still think this shunt and monitor business is a bit of sorcery but am committed to getting the damn gauge to quit lying to me. Have learned a lot from your posts and the links you sent me to. Mahalo for your help.

Now I have to find some of those large fuses to put in the positive side of the battery leads.

[exMaggieDrum]

[QUOTE=roverhi;1908293]
A few more questions on the shunt.:
1. The engine ground is led to the load side of the shunt. I thought that is what DeepFrz's illustration showed, but it may not, and thought I also saw that in one of Stu's Links. Somehow it doesn't seem right. Would think the engine ground would go on the battery side of the shunt. Which side does the engine ground wire go on??

The engine ground wire would go on the "load" side of the shunt, that is, NOT the battery side. The only wire/cable that should go to the house bank would be the battery side cable of the shunt. No other wires should go direct to the battery negative, at all, if you want to measure all the current in and out of the battery. This will not measure, or carry through the shunt, the starting current from a separate starter battery. It would measure any and all current going in and out of the house bank, including starting current if you parallel the batteries to start the motor when the start battery is down or offline. So the shunt needs to be rated for starter current. A 500A, and usually a 350A, shunt would be big enough.

2. Seems to me that with both start and house bank battery grounds (Negative) lead to the Battery Ground side of the shunt, the LinkPRO meter would read whatever battery bank is selected. Know that switching back and forth between house and start batteries would mess up any cumulative readings on the meter so the LinkPRO would have to be reset each time to get it to accurately show the history of that battery from then on. Seems like your suggestions that to get both batteries monitored I'd have to have two meters and two shunts would only be for constant simultaneous monitoring of both banks. Wouldn't that only be true for historical data and cumulative readings for each of the batteries??

When you switch between start and house batteries you are switching the battery positives, not the negatives. Your start battery negative should go either to the engine "ground" or to the main battery negative ground bus/stud. The house bank negative would go to that same point/circuit but only through the shunt first. When you start the motor with the start battery the complete circuit is from battery positive to battery switch to starter and then return via the engine block negative to the start battery. That current would NOT have to travel through the house battery shunt so the LinkPro would not see any current and would not measure that. If you paralleled the banks to start the LinkPro would measure the contribution of the house batteries to the starting, i.e. part by the start battery and part by the house. If you turned off the start battery and turned on the parallel switch (depending on how you have wired that), then the LinkPro would show the total start current.

Normally, a multimeter like the LinkPro would not be used to measure current to/from a start battery since it has a relatively uncomplicated life and is not used (normally) to power all the other circuits on a boat. Starting the motor is not a huge drain (unless the motor won't start) on the start battery. You do need to monitor the voltage of the start battery at a minimum. But your LinkPro should be able to measure the voltage of a second battery through a battery voltage sense wire (small fused) per the installation wiring diagram. You would NOT have a shunt for battery #2 (start battery).

If you do want to go full anal you could install a second LinkPro for the start battery but I wouldn't recommend it as it is way overkill. Battery voltage should be enough info to manage the health and welfare of the start battery. If you had two HOUSE banks you would need two LinkPro's, with two shunts.

3. The connection for the shunts is a 3/8" by 1/2" long bronze bolts. The bolts are too short to put more than two leads to a side. Can't find any 3/8" bronze/brass/copper bolts in Kona. Would it be a problem to use a 3/4" long stainless steel bolt if the 1/2" long bronze bolts prove too short?? Seems like that would work since the leads would be clamped to the Bronze/Brass/Copper chunk that makes up the body of the shunt.

You can use longer stainless bolts at your shunt, although you really only one since you will only have one cable on the battery side (per above). The only worry would be possible dissimilar metal issues but in practice I haven't seen that. I would suggest coating the threads with TefGel or Lanocote. And you are entirely correct in that the electrical connection should be from the cable lugs to the shunt top. You should never put a dissimilar washer underneath the cables between them and the shunt, nor between the cables. Electricity should never be forced to go through stainless - it is a poor conductor compared to copper or bronze (or tinned copper). You should use lock washers on the shunt. They usually come with them.

Yes, when it comes to wiring theory I'm a dunce. Never got much beyond the garden hose analogy of how electricity works. Believe it or not, have wired three different boats that I've sailed from Coastal Atlantic, Coastal California, SoPac and Transpac without any problems. Of course they were simple set ups without any sophisticated electrickery thrown in. Still think this shunt and monitor business is a bit of sorcery but am committed to getting the damn gauge to quit lying to me. Have learned a lot from your posts and the links you sent me to. Mahalo for your help.

When I started out working with electrical circuits, I had the same issues. In fact I still have them so I take a "dumb" approach to many new circuits or when troubleshooting a difficult issue. I sketch out the circuit and then "turn" switches on and off and trace where the electrons can or cannot flow based on the new pathways that are created. A good example is for bilge pump switches. I have done hundreds of installs and even more troubleshooting, yet I invariably will draw out the circuit - noting the wire colors and gauges. And then I play "guess the flow" game with them.

I have a funny situation on my boat that I will be doing that for this week. And it involves the shunt and battery negative side of the batteries in the house bank. I have three 8D batteries all connected in parallel (I thought) but I get a different voltage on the single battery on the starboard side compared to the voltage on the two batteries on the port side. I traced all the cables to diagram them right after I got the boat last year and thought I had it nailed. But the readings I am getting tell me there is some wiring that is different from what I thought I had.

Of course, it is the cables that run under and behind things so it will be a son of a gun to sort out. I used the old "run the finger along the cable" trick but somehow I goofed. Or there is something else more mysterious going on. I am hoping it is something simple and obvious. But the boat was wired in strange ways by the PO and on my list is to completely rewire (and move) the batteries and switches. So when I have that done it will be done 100% right and I'll know every detail for sure.

Now I have to find some of those large fuses to put in the positive side of the battery leads.

I am going to use the new (relatively) round fuses that fit at the battery terminals themselves. They are easy to install and don't take much space.

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[roverhi]

Okay, will run the start battery gnd. direct to the engine. Actually probably better as we are talking inches to the engine instead of feet to the shunt. The shunt must be able to handle the engine start battery amperage as it's been wired that way for years but will defer to greater wisdom.

Now on to better securing the batteries and adding two more GC batteries to handle the yet to be installed refrigeration drain.

Mahalo for all your help.

[DeepFrz]

roverhi, draw out your electrical system and then ask yourself what you will do if you should happen to need to start your engine with the house bank. Be careful you don't end up with ground loops but make sure that you can use the house bank to start, if that is what you want.