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Fitting Ammeter shunt


Johny London

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I'll need a short fly lead to connect my shunt resistor (on the -ve of the domestic battery bank) and it sets me wondering whether I should connect just the DC loads through the shunt, or the inverter feed as well. I already know whats going on with the ac thanks to a meter I have on that side of things. Can't quite envisage how I'll get best use out of the dc ammeter - wondering how others have wired up in these circumstances?

Also - anywhere online to order a thick patch lead for this (I've forgotten the ratings since I last mucked around with this sort of thing... 90mm2?)

ta

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1 minute ago, Johny London said:

I'll need a short fly lead to connect my shunt resistor (on the -ve of the domestic battery bank) and it sets me wondering whether I should connect just the DC loads through the shunt, or the inverter feed as well. I already know whats going on with the ac thanks to a meter I have on that side of things. Can't quite envisage how I'll get best use out of the dc ammeter - wondering how others have wired up in these circumstances?

Also - anywhere online to order a thick patch lead for this (I've forgotten the ratings since I last mucked around with this sort of thing... 90mm2?)

ta

EVERY NEGATIVE should go through the Shunt, otherwise how will you know what has been pulled out of the batteries (so you know how much to put back in) ?

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8 minutes ago, Johny London said:

I'll need a short fly lead to connect my shunt resistor (on the -ve of the domestic battery bank) and it sets me wondering whether I should connect just the DC loads through the shunt, or the inverter feed as well. I already know whats going on with the ac thanks to a meter I have on that side of things. Can't quite envisage how I'll get best use out of the dc ammeter - wondering how others have wired up in these circumstances?

Also - anywhere online to order a thick patch lead for this (I've forgotten the ratings since I last mucked around with this sort of thing... 90mm2?)

ta

The inverter is also a DC load so it has to go through the shunt.

What else did you think it was? 

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I know the inverter is a dc load, but it has it's own monitoring via a mains v/a meter. I only have a smart gauge so don't need to count amp hours in and out. Most times the inverter is off these days as I go increasingly 12v with stuff. So I suppose I'm leaning to the side of just putting it onto the dc - I'm not sure exactly how I will use the information - obviously for knowing when batteries are recharged (though I suppose I wouldn't be so sure if charging from shoreline but that is quite a rarity anyway).

The fatest lead I see on ebay is 345amp (50mm2) - is that enough for everything? I have a 500a shunt anyway. I have 90mm2 leads to the inverter, on about a 1.5 meter run. I guess I'm concerned about creating a weak spot in the wiring if I put the whole lot through the shunt and lead.

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Just now, Johny London said:

I know the inverter is a dc load, but it has it's own monitoring via a mains v/a meter. I only have a smart gauge so don't need to count amp hours in and out. Most times the inverter is off these days as I go increasingly 12v with stuff. So I suppose I'm leaning to the side of just putting it onto the dc - I'm not sure exactly how I will use the information - obviously for knowing when batteries are recharged (though I suppose I wouldn't be so sure if charging from shoreline but that is quite a rarity anyway).

The fatest lead I see on ebay is 345amp (50mm2) - is that enough for everything? I have a 500a shunt anyway. I have 90mm2 leads to the inverter, on about a 1.5 meter run. I guess I'm concerned about creating a weak spot in the wiring if I put the whole lot through the shunt and lead.

 

What is the reasoning behind fitting a shunt and ammeter ?

 

If the ammeter is not 'monitoring usage' and just giving 'spot' readings it wouldn't seem (to me) to be worth having.

 

19 minutes ago, Johny London said:

Can't quite envisage how I'll get best use out of the dc ammeter

 

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Oh, well mainly to see when the batteries are charged (taking under 5 amps) but also handy to find out what each item I have uses, so I can plan my energy usage (for example, deciding which small items I can afford to leave in standbye).

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18 minutes ago, Johny London said:

Oh, well mainly to see when the batteries are charged (taking under 5 amps) but also handy to find out what each item I have uses, so I can plan my energy usage (for example, deciding which small items I can afford to leave in standbye).

Have you got a 2-way ammeter ?

 

Otherwise you can only see amps-in, OR, amps-out.

 

A clamp meter would be far simpler (and probably cheaper) and more versatile than your shunt and ammeter and will give you the same instantaneous readings (but both in and out).

Edited by Alan de Enfield
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I have a */- 500A bBlue Sea meter which absolutely everything goes through.  The only way to know if or what the alternator/solar/charger are putting inot/out of the batteries/  I also have an ammeter on my DC panel which will tell me what the DC side of things are using. A third ammeter as well on the solar feed (I'm surprised how many people haen'y got a clue what their panels are producing, which may be why you see so many shaded by stuff on the roof).  A fairly easy bit of mental arithmetic then tells me how much my inverter is drawing.  i like to know what is going on.

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14 hours ago, Johny London said:

The meter I have will do both in and out :)

Then everything in and out should go through the shunt Johny, including the inverter (which will only be an "out" unless it's an inverter/charger). Just the one connection, the fly lead you refer to, on your domestic bank negative terminal running to one side of the shunt where it should again be the only connection. All other negative connections on t'other side of the shunt. Only this way will you see what current is actually going into/out of your batteries.

 

My heavy DC cables are in 70mm2 and when I was fitting my battery monitor shunt Debdale knocked me up that very same lead in a few minutes at very reasonable cost as I was passing - I'd phoned ahead rather than chanced my arm. I suspect many other yards would do the same if that's an option for you.

 

Hope that helps. :)

 

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Yes that's right - I have decided to go with the popular opinion and wire everything after the shunt. And my inverter charger has 90mm2 cable (think the cable to the dc stuff is like 50mm2 or something) so definitely want st least a 90mm2 link to the shunt.

However, trying to get hold of one is proving very difficult. I've tried two boat yards, a metal place (welding) and two car places. No one carries the cable, or can put one together (I have some suitable lugs already, or (in the case of one place) can be bothered.

No joy online either - Midland have the cable alone at £23 a meter! Was hoping to pay not more than that for the whole thing made up (only need 300mm or less). At this rate I might have another look to see if I can somehow get the shunt straight onto a battery terminal - I couldn't last time but now I know how difficult the link cable is I might try a bit harder.

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2 hours ago, Murflynn said:

any auto electrical workshop should have some offcuts of heavy battery cables in their bits bin, and can fit the terminals for you (without the terminals how do you intend to make the connections?)

Over the years I have heard lots of people say this kind of thing with respect to electrics, and woodworking, and stuff. Whenever I've popped into somewhere in the hope of something like this, I've usually been told it's not something that they do, or they would do it when they got round to it, which could be several days, or longer.

 

In fairness, I've probably only tried it in a couple of places before deciding I wouldn't bother again.

 

In a similar position to Johnys about 7 years ago, I bought the wire and the terminals on ebay, prepared the ends of the wire, and paid an auto electrical workshop to fit the terminals to the wire.

 

For any wires of 70mm2 or less, I buy the wire and terminals online, and I have a hydraulic crimper to fit the terminals.

 

he doesnt seem to want to spend any money, so my solution probably doesnt work for him :) 

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3 hours ago, Johny London said:

 - Midland have the cable alone at £23 a meter! Was hoping to pay not more than that for the whole thing made up (only need 300mm or less). At this rate I might have another look to see if I can somehow get the shunt straight onto a battery terminal - I couldn't last time but now I know how difficult the link cable is I might try a bit harder.

 

How much more do Midland want to crimp a terminal to each end? I don't know whether they provide that service but other good chandlers do for a few quid extra.

 

I ended up buying a set of big crimpers about 14 years ago for some ridiculous price. Never worked out why they were so expensive. I guess they're not a common household tool so don't benefit from economies of scale.

Edited by blackrose
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My connection is a few inches of 1" x 1/8" copper strip. Probably available on Ebay or from a lightning conductor supplier. You only need something big enough to carry the current,  whereas your inverter cables will probably be sized for volt drop.

 

Richard 

 

150mm of copper bar on ebay £4.99. Other sizes available. 

Edited by Ryeland
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I think I paid 13 quid at Debdale. I'd say you need a boatyard, not a chandlery supermarket (although some of the more "mom and pop shop" types may be able to help). Phone ahead to a couple you'll be passing and see what they can offer.

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12 hours ago, Ryeland said:

My connection is a few inches of 1" x 1/8" copper strip. Probably available on Ebay or from a lightning conductor supplier. You only need something big enough to carry the current,  whereas your inverter cables will probably be sized for volt drop.

 

Richard 

 

150mm of copper bar on ebay £4.99. Other sizes available. 

How does that work? Is one end of the strip attached to the battery terminal, then the various wires, (or shunt), connected to the other end of the strip?

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51 minutes ago, Richard10002 said:

How does that work? Is one end of the strip attached to the battery terminal, then the various wires, (or shunt), connected to the other end of the strip?

Hole in each end, one end on the battery terminal bolt, the other on the shunt terminal bolt. All cables to the other end of the shunt as usual. My shunt fits neatly in the 'gully' formed between the tops of two batteries.

Richard 

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13 hours ago, Ryeland said:

My connection is a few inches of 1" x 1/8" copper strip. Probably available on Ebay or from a lightning conductor supplier. You only need something big enough to carry the current,  whereas your inverter cables will probably be sized for volt drop.

 

Richard 

 

150mm of copper bar on ebay £4.99. Other sizes available. 

That's a really neat idea! I'll have a look at it all again when I tog up to paint in the engine bay.

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It was a few years ago now, but Midland Chandlers crimped the lugs onto the cable I was buying for free.  Reasonable enough really considering how quick and easy it is to do with the right crimper.

 I also had some lugs crimped by a chandler which fell off when I came to fit them. I tend to do them myself now using a Mole wrench, and never had a problem. Mind you I wouldn’t try that on 90 mm^2 cable.

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18 hours ago, blackrose said:

 

 

I ended up buying a set of big crimpers about 14 years ago for some ridiculous price. Never worked out why they were so expensive. I guess they're not a common household tool so don't benefit from economies of scale.

same here (£70).  now I see Chinese hydraulic crimpers on offer for a fraction of the price.  GRR !!

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As it was so difficult trying to source what I wanted, I did indeed have a harder try at making things fit as is. Managed to get the shunt to sit properly on the battery terminal itself, there was only one way it would go as its lug ends are very large - it's pointing away from where the cables go so a bit counter intuitive but there was enough play in the cables to do this and it is done up properly nice and tight.

Again though - what an absolute bitch of a job trying to do anything on those batteries - access is a joke. A ten minute job ended up taking an hour and a half, plus a few bumps and scratches.

Will be interesting to see what the current shows at various times. Just rea;ised I forgot to move the Webastos ground!

Shunt 1.JPG

Edited by Johny London
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8 hours ago, Johny London said:

Managed to get the shunt to sit properly on the battery terminal itself, there was only one way it would go as its lug ends are very large - it's pointing away from where the cables go so a bit counter intuitive but there was enough play in the cables to do this and it is done up properly nice and tight.

I think you have missed a bit.  There is no real problem having "battery - cable - shunt - other wires".

 

There is very little advantage connecting the shunt directly to the batteries, but there must not be any other connections between them. "Battery - cable - shunt - everything" is how it should be done.  Bolting the shunt to the battery terminals is in fact wrong!

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