Ammeter Negative Shunts?

xeitosaphil

xeitosaphil

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First let me apologise for posting so many post in the last few days, hopefully this will be the last for a while.

I can never get my head around Negative Shunts for some reason? That is, where to put them in relation to what you want to monitor!

I’m still in the throws of rewiring things re additional House battery and Starting etc, as per previous posts, and finally down to where to put the shunt for monitoring the Distribution Board discharge outputs and Domestic battery charge inputs.

Latest wiring Diagram will hopefully be the last included.

I have two diagrams one I made for the Anchor winch Post, and one which I amended the Engine ground cable for this post.

Can anybody tell me where I should fit the shunt to monitor the Distribution Board discharge outputs and Domestic battery charge inputs?

Position 1, or Position 2 on the Shunt Post Diagram, or Position 3 on the Anchor Winch Diagram. Or should it go somewhere completely different


Cheers Philip
 
pvb said:
Position 1.
Click to expand...

Thanks pvb/ sailorman,



Would it still be the same if I put the Negative shunt on the other end of the domestic battery bank- on the battery on its own ( ex Engine Batt ) as long as the Distribution board feed was before the shunt and there was nothing between the shunt and the battery?

Only someone has said to me that the negative return to the battery bank should be on the opposite end to the positive feed out of the battery bank.

The Engine ground would then come off the “ L” pair, straight to the Negative stud.

Philip
 
If you wish to measure the current flow into and out of the batteries there must be no other connection between the negative of the batteries and the shunt.

If there is more than one battery all the negative posts of the batteries must be connected together and then to the shunt.

I have 2 banks of 6 batteries each and a shunt for each bank. The negatives of each bank are connected together then to the respective shunt then the others side of each shunt is connected to a 1 2 both switch. I normally run with the 1 2 both switch in the both position but I can still see how much current if flowing into / out of each battery bank.

If you have any feed off to any other section between the shunt and the battery negative the meter/shunt will not include that current on the meter.
 
xeitosaphil said:
Would it still be the same if I put the Negative shunt on the other end of the domestic battery bank- on the battery on its own ( ex Engine Batt ) as long as the Distribution board feed was before the shunt and there was nothing between the shunt and the battery?

Only someone has said to me that the negative return to the battery bank should be on the opposite end to the positive feed out of the battery bank.

The Engine ground would then come off the “ L” pair, straight to the Negative stud.
Click to expand...

No, that wouldn't work. The shunt would monitor current used by the distribution panel, but not any charging current to the batteries.

The notion that positive and negative feeds should be taken from opposite ends of a battery bank is theoretically sound, but in practice it makes little difference with only 3 batteries as long as the interconnections are sound. It's a bit OTT, but OK if you want to sound clever, and indeed the truly clever people have devised even more complex ways of wiring multiple batteries. Having said that, I had a bank of 6 batteries on my last boat, and I did take the positive and negatives feeds from opposite ends.
 
pvb said:
It's a bit OTT, but OK if you want to sound clever, and indeed the truly clever people have devised even more complex ways of wiring multiple batteries.
Click to expand...

It seems I was the "someone" who suggested this in the other thread.
Guess I must have annoyed you in some way, but I'm not clever enough to figure out how...
 
BabaYaga said:
It seems I was the "someone" who suggested this in the other thread.
Guess I must have annoyed you in some way, but I'm not clever enough to figure out how...
Click to expand...

Not at all, nothing to do with you, it's often suggested, and people usually quote the Smartgauge guy whose name I forget, but the reality is that for 3 or 4 batteries it makes an insignificant difference. The theory is correct, it's the practicality that's missing. And this is supposedly a "practical" forum.
 
pvb said:
No, that wouldn't work. The shunt would monitor current used by the distribution panel, but not any charging current to the batteries.

The notion that positive and negative feeds should be taken from opposite ends of a battery bank is theoretically sound, but in practice it makes little difference with only 3 batteries as long as the interconnections are sound. It's a bit OTT, but OK if you want to sound clever, and indeed the truly clever people have devised even more complex ways of wiring multiple batteries. Having said that, I had a bank of 6 batteries on my last boat, and I did take the positive and negatives feeds from opposite ends.
Click to expand...

This is my final attempt to get it in the right position to monitor domestic bank charges and discharges with the wiring from opposite ends of the battery. ( if this doesn’t work I will have to go with your suggestion in Post 2 )

The reason being is that the stand alone battery is approx 1.5mtrs cable length away from “ L “ shaped set and I am trying to make the charging and paralleling of the batteries as efficient as possible under the difficult situation regarding space in which to site it.
Not sure if the advantage of the proposed position will help with charging efficiency, but the distance of the additional battery from the existing bank is causing me a little concern.

Incidentally I plan to use 50mm2 link cables which I assume will be adequate?

Cheers Philip
 
xeitosaphil said:
This is my final attempt to get it in the right position to monitor domestic bank charges and discharges with the wiring from opposite ends of the battery. ( if this doesn’t work I will have to go with your suggestion in Post 2 )

The reason being is that the stand alone battery is approx 1.5mtrs cable length away from “ L “ shaped set and I am trying to make the charging and paralleling of the batteries as efficient as possible under the difficult situation regarding space in which to site it.
Not sure if the advantage of the proposed position will help with charging efficiency, but the distance of the additional battery from the existing bank is causing me a little concern.

Incidentally I plan to use 50mm2 link cables which I assume will be adequate?
Click to expand...

Whilst this takes the feed from opposite ends of the bank, the charging goes to the same end. If anything, I'd suggest it's better to have the charging going to opposite ends, as the current is higher, although with 50 sq mm connecting cable you won't have a major problem with voltage drop. Frankly, unless you move the alternator output to the other end of the bank, which I understand will be difficult, you'd be best going with Position 1 in the diagram in your original post.
 
pvb said:
Whilst this takes the feed from opposite ends of the bank, the charging goes to the same end. If anything, I'd suggest it's better to have the charging going to opposite ends, as the current is higher, although with 50 sq mm connecting cable you won't have a major problem with voltage drop. Frankly, unless you move the alternator output to the other end of the bank, which I understand will be difficult, you'd be best going with Position 1 in the diagram in your original post.
Click to expand...

Thanks pvb,

I'll go with your suggestion for Position 1 then because moving the alternator cable is not easily achieved and the shunt at present is in close proximity to the domestic bank anyway. If I find that I need to replace the alternator cable to the 25mm2 cable size you suggested in an earlier thread, I could alter things about again then.

I can alter the Shore powered battery charger feeds though, to opposite ends of the bank if you think this would be beneficial if and when it is used?


Thanks for your patience and all your help, its much appreciated. :encouragement:

Cheers Philip
 
Hope fully this won't confuse being as you've got your answer but it may help. An Ammeter is the electrical equivalent of a flow-meter. Think of your battery(s) as water tanks and your various appliances and electrical gadgets as taps and showers, etc. The cables are the pipes.

If you want to know how many gallons per hour you are using from a particular tank (and therefore what's remaining after you filled it) you have to measure the flow from the one pipe that comes straight from the tank. If you put the flowmeter in the pipe to the galley tap then you'll only measure what that tap uses, not what's leaving - you won't measure what the shower or the heads taps use, etc. Obviously. if you wanted to measure what the heads uses then you would put the flowmeter in the pipe to the heads.

Likewise, if you have two tanks, unless you connect take the feed from both tanks together and then have a single feed that is effectively from both tanks, you'll only measure the flow from from one tank and never know what water has been taken from the other tank. In other words you have to join the batteries together at the terminal (don't try this with a 24 volt system please - we're talking 12V batteries and 12V systems!!).

The analogy isn't perfect but it's more than adequate for working out where to put the shunt.
 
grumpy_o_g said:
Hope fully this won't confuse being as you've got your answer but it may help. An Ammeter is the electrical equivalent of a flow-meter. Think of your battery(s) as water tanks and your various appliances and electrical gadgets as taps and showers, etc. The cables are the pipes.

If you want to know how many gallons per hour you are using from a particular tank (and therefore what's remaining after you filled it) you have to measure the flow from the one pipe that comes straight from the tank. If you put the flowmeter in the pipe to the galley tap then you'll only measure what that tap uses, not what's leaving - you won't measure what the shower or the heads taps use, etc. Obviously. if you wanted to measure what the heads uses then you would put the flowmeter in the pipe to the heads.

Likewise, if you have two tanks, unless you connect take the feed from both tanks together and then have a single feed that is effectively from both tanks, you'll only measure the flow from from one tank and never know what water has been taken from the other tank. In other words you have to join the batteries together at the terminal (don't try this with a 24 volt system please - we're talking 12V batteries and 12V systems!!).

The analogy isn't perfect but it's more than adequate for working out where to put the shunt.
Click to expand...

But please, please, please note that although you measure water flow rates in gallons, or litres, per hour you measure electricity flow rates in amps ..... not amps per hour!
 
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