Ammeter - advice needed

[Johny London]

I got my ammeter hooked up finally (another thread on that).

The problem is that it is showing -5a when everything is switched off. I'm trying to ascertain if it's a miss calibrated meter or if I am actually loosing current to somewhere (would certainly explain my battery woes over the years!).

 

I can't easily remove the grounds one at a time (dreadful access to batteries) so I have worked the other way, methodically trying to eliminate things from +ve supplies.

1. Switched off 12v circuit breakers one at a time, then the master switch within the unit (it's a consumer unit style one).

2. I disconnected the inverter (on it's +ve supply, it was already switched off anyway). It always does a big spark so I know it uses something even when off).

3. Disconnected Webasto at its multi pin plugs.

4. Switched off an isolator switch in the engine bay (NOT the starter battery one, but one that is fed from the domestic bank and appears to go to the engine with a loom of wires - I can't remember what this is for, see pic below).

 

That accounts for all the equivalent negative wires that are connected to the leisure bank.

 

So, I am at a loss as what to work next - everything is off, yet the ammeter is -5a (obviously I disconnected the solar too). When the solar is on, it might show say 5 or 6 amps going into the batteries (on the mppt display) but there will still be a deficit on the ammeter (ie -3 or -4a). When the fridge cycles on, and there is good solar, I get what I'd expect, minus that extra 5 amps, so it seems to be ever present as far as I can deduce (obviously when the system is all on, it's dynamic and hard to be exact as things change from moment to moment).

 

As far as the mis calibrated meter idea goes, disconnecting the sense wires but leaving the unit powered causes it to read zero. The meter does read +ve when the panels are doing ok, but I'd say still by less the 5 amps.

 

Am I wasting my time, just a faulty meter? Or are there things I haven't considered yet? Felt sure that a logical process of disconnecting would yield results but not so far. 

I know someone will say the only way is to take off the negative leads one at a time but I think I achieved the same thing with the positives of the relevant circuits? I can't get in there easily - let alone with my dvm in ammeter mode, for example.

 

I'm beginning to lean towards a duff meter, even as I fiddled, the soc has gone up by 2% despite the ammeter reading in the -ve

 

Here's a picture of the isolator switch in the engine bay.

 

[MtB]

13 minutes ago, Johny London said:

I'm beginning to lean towards a duff meter

 

I'd say you genuinely have a mystery 5A drain on your batts.

 

The ammeter doesn't actually measure current directly, it derives it by measuring the (tiny) voltage dropped across the shut. The voltage across the shut is zero when no current is flowing through it, and as the current climbs so does the (tiny) voltage across it. So the ammeter display is a voltmeter really, but calibrated in Amps.

 

The fact that it shows zero when disconnected tells us it reads zero current correctly, and when you connect it to the shunt it gets a reading, so you MUST have a current flowing. 

 

Now you need to get on and find it! Do you have a clamp meter? 

 

 

[Alan de Enfield]

15 minutes ago, Johny London said:

 

 

 

Not an answer to your question, BUT :

 

It looks as it you are tapped into every battery in the bank separately.

 

battery 1 powers the Inverter

battery 2 powers the mystery switch

battery 3 powers the domestic 12v system

battery 4 (along with battery 1) also powers the inverter

 

It would appear to be a very unusual method of wiring.

Is there some logic in it ?

[MtB]

This is one of the many situations when a DC clamp meter is invaluable.

 

 

[IDS]

Assuming your sense leads are normally connected to a shunt ( a fat conductor inserted in series with your battery negative lead), then after you disconnect them from the shunt connect them to each other and check your meter still shows zero.

[WotEver]

40 minutes ago, Mike the Boilerman said:

This is one of the many situations when a DC clamp meter is invaluable.

Agreed. I was about to make a couple of suggestions but the best suggestion is the one you’ve already made - get a clamp meter. 

 

Just for a change, here’s a clamp meter that isn’t the UT 210e:

https://www.amazon.co.uk/dp/B076HLZ3XZ/ref=cm_sw_r_cp_api_i_ekjmDbDWB6Q20

[Johny London]

Just did the shunt test suggested above - the ammeter does still read zero when the shunt connections are joined together (as well as o/c).

 

To answer Alan - no the batteries are conventionally wired, as in the starter is on its own, the other four paralleled. What might look confusing is that the dc supply comes off one +ve terminal, (fourth leisure battery) and the supply to the inverter comes off two other ones (first and third leisure batteries) and mystery switch off the second, but they are all linked.

I can't remember what or why the mystery switch is as it is, but it was like that from new - then again I've always had battery problems which we all put down to my own stupidity!

If it did turn out that there really was a 5a drain I would feel rather vindicated - and possibly have been rather too hard on lead acid technology!

 

I think a clamp meter would be very useful - annoyingly, I actually have one but it doesn't do DC current. Anything else I could be missing?

[MtB]

1 minute ago, Johny London said:

 

I think a clamp meter would be very useful - annoyingly, I actually have one but it doesn't do DC current. Anything else I could be missing?

 

Then you don't really have a clamp meter. The really useful feature is DC current. Everything else on it is just fluff.

 

 

(Assuming you have an ordinary DVM too, that is!)

 

 

[Alan de Enfield]

6 minutes ago, Johny London said:

To answer Alan - no the batteries are conventionally wired, as in the starter is on its own, the other four paralleled. What might look confusing is that the dc supply comes off one +ve terminal, (fourth leisure battery) and the supply to the inverter comes off two other ones (first and third leisure batteries) and mystery switch off the second, but they are all linked.

That is what I was referring to.

 

"Normal" would be running a single positive to a Busby (Bus-Bar) and then connecting everything to the Busby.

Your way would appear to be putting variable loads on the batteries - very unconventional.

[nicknorman]

15 minutes ago, Johny London said:

Just did the shunt test suggested above - the ammeter does still read zero when the shunt connections are joined together (as well as o/c).

 

To answer Alan - no the batteries are conventionally wired, as in the starter is on its own, the other four paralleled. What might look confusing is that the dc supply comes off one +ve terminal, (fourth leisure battery) and the supply to the inverter comes off two other ones (first and third leisure batteries) and mystery switch off the second, but they are all linked.

I can't remember what or why the mystery switch is as it is, but it was like that from new - then again I've always had battery problems which we all put down to my own stupidity!

If it did turn out that there really was a 5a drain I would feel rather vindicated - and possibly have been rather too hard on lead acid technology!

 

I think a clamp meter would be very useful - annoyingly, I actually have one but it doesn't do DC current. Anything else I could be missing?

The shunt is a very low resistance and in the absence of any current flow, connecting the sense wires to it should be indistinguishable from connecting them together.

 

Well nearly so. Try connecting both sense wires to one side of the shunt. Of course one would expect it to still read zero, but due to the way the electronics works it might not.

 

If it does still read zero, there is definitely 5A going astray somewhere.

[Johny London]

I cant do that last thing without getting right in there again. It's quite agonising.

In the meantime, I discovered that the mystery switch simply turns off the feed from the alternator! Why would I want to do that?

I didn't think there was anything unusual about just daisy chaining the batteries (though appreciate it is not the theoretical ideal). Different take off terminals for convenience of fittings really.

I've got a feeling it'll turn out to be something stupid like one of the batteries extra knackered (but that would still show current being drawn in not out?) or something similar.

I did find a cracked battery terminal thing...

[IDS]

So you really do have a mystery 5 A drain. That's quite a lot. You now have an in circuit ammeter that you know works, so start by taking off each positive lead going to your battery bank until the 5A drain stops.  Then follow that cable !

[WotEver]

47 minutes ago, IDS said:

So you really do have a mystery 5 A drain. That's quite a lot. You now have an in circuit ammeter that you know works, so start by taking off each positive lead going to your battery bank until the 5A drain stops.  Then follow that cable !

Much MUCH easier and quicker to use a clamp ammeter. If OP bought the one I linked to earlier he’ll have it tomorrow. 

55 minutes ago, Johny London said:

I did find a cracked battery terminal thing...



Replace it ASAP. It will completely unbalance your bank. 

57 minutes ago, Johny London said:

the mystery switch simply turns off the feed from the alternator! Why would I want to do that?

You wouldn’t. But the BSS insists on it. 

[Johny London]

Good idea taking off the positives one by one - as they are quite a lot easier to get to than the negatives! I'll do that. I did think I'd "effectively" done that already with switching things off, but evidently not!

I'm loath to by another meter, but if I can't get anywhere with the above method, at least it is an option.

 

Yeh, I need to get that terminal thing changed asap, that's for sure.

 

Hey the ammeter said -175a when the dishwasher was mid cycle! Cool.

[Alan de Enfield]

1 minute ago, Johny London said:

 

 

Hey the ammeter said -175a when the dishwasher was mid cycle! Cool.

That'd be about 1750 watts then.

[Johny London]

Yeh I know, cos I've also got one of those 240v ac meters  About 1859w.

[MtB]

13 minutes ago, Johny London said:

I'm loath to by another meter,

 

Jeez, why not try working with one hand tied behind your back whilst wearing a blindfold, too....? 

 

 

[Johny London]

Been doing that all afternoon - as in limited movement and vision - the engine bay painting is most tedious.

[system 4-50]

4 hours ago, Johny London said:

. I disconnected the inverter (on it's +ve supply, it was already switched off anyway). It always does a big spark so I know it uses something even when off).

Minor detail but no it doesn't.  It just charges up its capacitor thingy when you make the connection. It is an insignificant one-time event.  Confirmation from a guru requested.

 

 

What sort of device could be using 5A continuous?  Fridge & webasto are non-continuous. Headlight?  Curling tongs?

Edited July 18, 2019 by system 4-50

[WotEver]

5 minutes ago, system 4-50 said:

What sort of device could be using 5A continuous?

Central heating pump, mains fan...

6 minutes ago, system 4-50 said:

Minor detail but no it doesn't.  It just charges up its capacitor thingy when you make the connection. It is an insignificant one-time event.  Confirmation from a guru requested.

Depends. Some of ‘em use 5A just sitting doing nothing. 

35 minutes ago, Johny London said:

I'm loath to by another meter

When you eventually cave in and buy one you’ll wonder how you ever coped without one. 

[system 4-50]

1 hour ago, WotEver said:

Depends. Some of ‘em use 5A just sitting doing nothing. 

not when switched off as per the original comment.

[chevron]

I fitted a victron 712 thought I had a drain on my battery’s but I had to charge batteries till full make sure everything was off including solar panel input and waited an hour and reset worked fine since.

[blackrose]

1 hour ago, WotEver said:

When you eventually cave in and buy one you’ll wonder how you ever coped without one. 

 

Considering the cramped conditions, poor access to batteries and physical agony that the OP was moaning about earlier it does make one wonder. I can understand why someone would be loathe to buy the same meter twice but it's something that would be useful in the circumstances as he'd be able to take readings without being right on top of the batteries.

 

I've got loads of different bits of kit that I only use occasionally. Things like IR temp gauge, clamp meter, plug in polarity tester, big crimpers, and countless tools that only come in handy now and then, but when they do they're invaluable. My boat is my home and my hobby so I have no problem spending money on bits and pieces. Mind you, I don't drink much or smoke. I've got neighbours who seem to hate spending money on their boats but have always got a spliff or can of cider in their hands. Each to their own I guess but I hate if when they come asking for stuff.

Edited July 18, 2019 by blackrose

[WotEver]

1 minute ago, blackrose said:

I've got loads of different bits of kit that I only use occasionally. Things like IR temp gauge, clamp meter, plug in polarity tester, big crimpers, and countless tools that only come in handy now and then, but when they do they're invaluable. My boat is my home and my hobby so I have no problem spending money on bits and pieces.

I’m much the same. I spent several hours rearranging the plumbing for a new sink yesterday. Soldering copper pipes etc. I used my blowtorch, solder mat, flux and solder for the first time in a few years, but if I didn’t have them then the job couldn’t have been done without waiting days for a plumber and then paying him a few hundred quid. 

 

As for multimeters, last time I counted I have nine, I think. All but two of them work, only one has a D.C. clamp, and only one of them has been recently calibrated. 

20 minutes ago, system 4-50 said:

not when switched off as per the original comment.

They can’t charge their caps if they’re switched off though either. 

[blackrose]

12 minutes ago, WotEver said:

 

 

As for multimeters, last time I counted I have nine, I think. All but two of them work, only one has a D.C. clamp, and only one of them has been recently calibrated. 

 

I've only got two; a cheapo and a fluke. Guess which one gets lent to neighbours?

 

I bought a digital IR rev meter from Amazon for 11 quid about a year ago. Using that I worked out that the revcounter on the boat was completely wrong and had never been calibrated and it helped me understand what happened to all my "missing" revs. I doubt I'll ever use it again but it was still worth the money. Potentially saved me hundreds of pounds repitching the prop again to get some more revs out of the engine.

Edited July 18, 2019 by blackrose