Measuring consumption?

[Joshua]

We want to test the consumption and current (amps) data given by our battery monitor, we have established that the monitor is giving reliable voltage readings but we suspect everything else.

 

What, in these circumstances, is the most reliable way to measure our electricity consumption and the current readings?

 

We live on board 24/7 so are on hand to run any type of test even if it means monitoring over extended periods of time.

 

I have in mind isolating all sources of consumption and then plugging in a device that has a reliable current demand and leaving it on for say 6 hours and seeing how the calculated draw compares with the monitors measured figures.

 

Would this produce any meaningful data that I could use to interpret the monitors measurements on a daily basis?

 

 

 

 

Joshua

[Arthur Brown]

What kind of circuit protection do you have? There are meter breakouts adaptors (Maplin etc ) for some fuse sizes to enable a meter to be inserter for short term readings.

 

Beware over reliance on amphour counting, it's usual to have to put more amp hours in than you can take out of a battery. Counting them out and in again is one of the fastest ways of bumping on the bottom of your battery capacity and letting it sulphate beyond reuse.

[Gibbo]

You can check the amps reading by putting a sensitive voltameter across the shunt. A normal multimeter is unlikely to have a low enough range for this so you'll need borrow a better one.

 

To check the amp hour counter in your monitor, the only way to do that is with another amp hour counter.

 

Have you checked your shunt wiring yet? I still thank that is your problem.

 

ETA. In fact I'll so far as to say that you're ignoring what people are saying and going on a big wild goose chase following red herrings.

 

Check your bloody shunt!

Edited September 20, 2012 by Gibbo

[Joshua]

You can check the amps reading by putting a sensitive voltameter across the shunt. A normal multimeter is unlikely to have a low enough range for this so you'll need borrow a better one.

 

To check the amp hour counter in your monitor, the only way to do that is with another amp hour counter.

 

Have you checked your shunt wiring yet? I still thank that is your problem.

 

ETA. In fact I'll so far as to say that you're ignoring what people are saying and going on a big wild goose chase following red herrings.

 

Check your bloody shunt!

 

I understand your frustration Gibbo, but I simply lack the talent, so am trying to do things I can understand.

 

We are heading back to the yard that fitted the system so that they can have a look. We won’t, however, be there until November and I want to make good use of the intervening time.

 

I attempted to map the wiring a couple of days ago following your and Nicknormans’ advice but to be honest got stuck immediately when I followed my first cable back to an isolation switch with 8 cables connected and no way of tracking each without dismantling the switch. Much of the cabling is also behind panels, for someone who understands electronics I guess they would be able to accurately predict where these go by noting where they exit but I would have to laboriously follow the cable like a ball of wool!

 

I need a quiet day to have another go when I can isolate everything to avoid an accident.

 

We are due to have a couple of little brackets welded to the boat soon and this will entail disconnecting our batteries, that may be my opportunity to have another go at mapping the system.

 

In the mean time, I’ll try measuring the current as you describe.

 

My multi-meter spec reads as follows:

 

DC Current 200mA-20A (max Measurement = 10A) +/- 1.5% of reading and +/- 0.5% of full scale.

 

Is this adequate?

 

It also says, “to measure current, you must break the circuit and connect the leads in series with the resulting two circuit connection points. Never connect the leads across a voltage source….”

 

Does this mean I have to disconnect one side of the shunt and is it not a voltage source?

 

 

 

 

Joshua

 

 

[Gibbo]

Pay attention!

 

I said...

 

You can check the amps reading by putting a sensitive voltmeter across the shunt.

 

If you try to measure the current using the ammeter on your multimeter you will simply blow it to pieces.

 

Check your shunt wiring. That's where the problem is.

 

We are due to have a couple of little brackets welded to the boat soon and this will entail disconnecting our batteries,

 

Why?

 

Disconnecting the batteries will achieve absolutely nothing. It's what "engineers" who don't know what they're talking about do

[nicknorman]

You can check the amps reading by putting a sensitive voltameter across the shunt. A normal multimeter is unlikely to have a low enough range for this so you'll need borrow a better one.

 

To check the amp hour counter in your monitor, the only way to do that is with another amp hour counter.

 

Have you checked your shunt wiring yet? I still thank that is your problem.

 

ETA. In fact I'll so far as to say that you're ignoring what people are saying and going on a big wild goose chase following red herrings.

 

Check your bloody shunt!

Wot e said plus, if you really wanted to, you could check the instantaneous current readout on the amphour counter against a know load, checking with a clamp meter. There is no point in spending time checking the monitor's software's ability to integrate current into charge!

 

The problem is almost certainly that current is getting into or out of the batteries not via the shunt., so checking it with a load that does go through the shunt is pointless.

[Joshua]

What kind of circuit protection do you have? There are meter breakouts adaptors (Maplin etc ) for some fuse sizes to enable a meter to be inserter for short term readings.

 

Beware over reliance on amphour counting, it's usual to have to put more amp hours in than you can take out of a battery. Counting them out and in again is one of the fastest ways of bumping on the bottom of your battery capacity and letting it sulphate beyond reuse.

 

Thanks for that Arthur, I don’t know the technical name for our type of fuse, but they are labelled ‘hager’.

 

Same for both 220VAC and 12VDC circuits.

 

As to counting amps in and out, I have read enough threads on here to know the folly of that, even my victron manual warns me of the unreliability.

 

What I really want is to be able to measure just how much I am pulling out of my system for any given 24 hr period, maybe I am using a lot more than I think?

 

I don’t believe that is the case but I want physical evidence not just my gut feeling.

 

 

 

 

Joshua

 

 

 

Pay attention!

 

I said...

 

 

 

If you try to measure the current using the ammeter on your multimeter you will simply blow it to pieces.

 

Check your shunt wiring. That's where the problem is.

 

 

 

Why?

 

Disconnecting the batteries will achieve absolutely nothing. It's what "engineers" who don't know what they're talking about do

 

 

 

Must try harder, I misunderstood when you said "A normal multimeter is unlikely to have a low enough range for this so you'll need borrow a better one."

I am of course taking advice from the welder, what precautions if any must I take to protect my electrics from the arc welder?

Joshua

 

 

Wot e said plus, if you really wanted to, you could check the instantaneous current readout on the amphour counter against a know load, checking with a clamp meter. There is no point in spending time checking the monitor's software's ability to integrate current into charge!

 

The problem is almost certainly that current is getting into or out of the batteries not via the shunt., so checking it with a load that does go through the shunt is pointless.

 

Is it possible to be wired in such a way that say the 12v system passes through the shunt but not the 220V or vicer versa?

I'll look up 'clamp meter', I am imaging that it is an instrument into which an appliance can be plugged so that its amp draw can be measured directly and accurately?

Joshua

[RLWP]

<snip>

 

Is it possible to be wired in such a way that say the 12v system passes through the shunt but not the 220V or vicer versa?

 

<snip>

 

Joshua

 

Yes, that is very, very possible. Or some other 12V circuit taking current that isn't passing through the shunt. This will mess your amp hour counter up completely

 

In fact, as others have said, this is almost certainly what your problem is

 

Have you any photos of your shunt?

 

Richard

[Arthur Brown]

http://www.maplin.co.uk/car-fuse-adaptor-lead-set-217881

[nicknorman]

 

Is it possible to be wired in such a way that say the 12v system passes through the shunt but not the 220V or vicer versa?

I'll look up 'clamp meter', I am imaging that it is an instrument into which an appliance can be plugged so that its amp draw can be measured directly and accurately?

Joshua

 

Yes definitely!

 

A clamp meter is a handy meter with opening jaws that can be clamped round a wire. It can measure current, thus avoiding having to break into the wire. Good for measuring large currents to a modest accuracy. They can be expensive, but are available on eBay from china for £25 to £30 (probably fakes, but they work well!). Be careful to get one that measures dc current, not just AC. Here is an example on eBay. It's the type I have and you can't beat it for the money.

Edited September 20, 2012 by nicknorman

[Richard10002]

Joshua,

 

As a lay person with a bit of experience of boats, unless I am missing something, this is fairly straightforward. It strikes me that you are avoiding stuff because it seems difficult, and then trying to reinvent the wheel.

 

You say that lots of wires are hidden, which is the case for many of us:

 

Can you see the cable that goes from your domestic battery negative terminal to your shunt? That should be the only cable that attaches to the domestic battery negative terminal, and to that side of the shunt. Any other cables which normally need to be attached to the domestic negative battery terminal should be attached to the other side of the shunt. In fact, the other end of the shunt takes the place of the domestic battery negative terminal, which seems strange, but it's true.

 

So you should have one thick cable from the battery end of the shunt to the battery and, probably, several other cables from the other end of the shunt to a variety of places.

 

I'll modify this to add that the thin battery monitor cables will be attached across the shunt, so the pedantic amongst us could say that there is more than one cable at the domestic battery end of the shunt.

 

If the above is correct, you are halfway there. If you can't see to check the above, you need to do something to check. - However, I am assuming that you can see the whole of the shunt - both ends. And you can see how many cables are attached to each end of it.

 

Once you have got one cable from battery negative to shunt, and several cables from the other end of the shunt, you need to make sure the monitor cables are connected correctly to the shunt. They will almost certainly be coloured, and various colours will attach to the battery end of the shunt or to the other end of the shunt. The thin monitor cables are usually connected to the shunt by small terminals, rather than to the big terminals at each end of the shunt.

 

If you have got all of this correct, your monitor should read correctly, both amps in and out, and voltage. If you doubt the amps in and out, get a cheap clamp meter, it will be accurate enough to measure charging amps, (amps in), as these are usually in the tens of amps, and it will also give a reasonably accurate guide to amps being used. If there is a wild difference between either reading, then perhaps your monitor is at fault.... But the odds are that it's somewhere in the wiring.

 

I am tempted to suggest that, if the above is beyond you, for whatever reason, you need to get a boat electrician in - not a welder, with all due respect to the welder.

 

I've got the clamp meter that Nick refers to. It was from Hong Kong, and works fine - it needs zeroing before using the amp meter facility.

 

Can you take a photo of your shunt, so we can see all of it, including a section of the cables at both ends. A photo of the negative terminal of your domestic battery bank would also be helpful.

 

You can upload to photo bucket, then link to them in a post here on the forum.

 

These pictures would answer a lot of questions, and help confirm, or eliminate, some of the conclusions being reached here.

[Joshua]

Yes, that is very, very possible. Or some other 12V circuit taking current that isn't passing through the shunt. This will mess your amp hour counter up completely

 

In fact, as others have said, this is almost certainly what your problem is

 

Have you any photos of your shunt?

 

Richard

 

Here are the main components, not sure it will tell you much.

The fuse box is part of the old original installation.

 

 

Joshua

 

 

 

 

 

 

 

 

 

 

 

[smileypete]

We want to test the consumption and current (amps) data given by our battery monitor, we have established that the monitor is giving reliable voltage readings but we suspect everything else.

 

What, in these circumstances, is the most reliable way to measure our electricity consumption and the current readings?

 

We live on board 24/7 so are on hand to run any type of test even if it means monitoring over extended periods of time.

Set the multimeter to the 20A range, connect in series with a car headlamp bulb or similar on the load side of the shunt. Check the current on the multimeter matches the current read by the batt monitor.

 

Now, make sure there are NO connections on the batt side of the shunt except the shunt sense connection and the batt bank itself.

 

If that checks out, give the batts a FULL charge then plug something into the inverter that pulls about 33A from the batt bank. The batt voltage should hold up for up to 20 hours, if it collapses well before then, your 660Ah batt bank is well down on capacity for some reason.

 

cheers, Pete.

~smpt~

[Gibbo]

I am of course taking advice from the welder, what precautions if any must I take to protect my electrics from the arc welder?

 

To be entirely certain you must make sure the entire electrical system is disconnected from the hull. That can be easy, it can also be a lot of work. It depends on the insatallation.

 

Whether or not the batteries are connected or disconnected is completely, totally, and absolutely utterly irrelevant. It makes absolutely no difference whatsoever. You might as well make sure all the jam jar lids are on tight. It's about as relevant.

 

Whether there is risk of damage depends upon where the welding is being done, and where the welder puts his earth clamp.

 

Now, make sure there are NO connections on the batt side of the shunt except the shunt sense connection and the batt bank itself.

 

This is the bit we keep asking for.

[Richard10002]

OK, it looks like there is only one cable coming off the left hand end of the shunt - does that go to the negative terminal of the domestic battery bank... And is it the only wire that connects to the negative terminal of the domestic battery bank?

 

Photo of the negative terminal of the battery bank?

[nicknorman]

OK, it looks like there is only one cable coming off the left hand end of the shunt - does that go to the negative terminal of the domestic battery bank... And is it the only wire that connects to the negative terminal of the domestic battery bank?

 

Photo of the negative terminal of the battery bank?

.... and in particular check that the -ve of the domestic battery bank is not connected to the -ve of the engine battery.

[Joshua]

OK, it looks like there is only one cable coming off the left hand end of the shunt - does that go to the negative terminal of the domestic battery bank... And is it the only wire that connects to the negative terminal of the domestic battery bank?

 

Photo of the negative terminal of the battery bank?

 

Yes and Yes (except of course for the wire connecting to the next battery negative in the bank)

 

.... and in particular check that the -ve of the domestic battery bank is not connected to the -ve of the engine battery.

 

confirmed.

 

Are there any issues with having a bank split up physically? I have effectively two sets of 3. Three batteries side by side then 3 end to end that actually span over the top of the 3 below so there are longer cables between the two sets than between the individual batteries, would this make any difference? Clutching at straws I know.

 

Joshua

 

PS

Is it possible to say what the voltage and current figures should read when a 660v bank is considered fully charged?

 

I am in the middle of a VERY long recharge at the moment (another one! just about to set off on a little cruise with batteries currently indicating a charge of 14.48V and a current of 4amps so it bloody well will be fully charged by the time I stop!) I will then take careful note of every appliance used for the next 12 hours. At least I will have a good starting point and may be able to rule out one factor, namely; much greater domestic consumption than I am guestimating. It still won’t explain where my monitor got its LSD from, but it’s a start.

 

Joshua

 

 

Edited September 20, 2012 by Joshua

[smileypete]

Is it possible to say what the voltage and current figures should read when a 660v bank is considered fully charged?

 

I am in the middle of a VERY long recharge at the moment (another one! just about to set off on a little cruise with batteries currently indicating a charge of 14.48V and a current of 4amps so it bloody well will be fully charged by the time I stop!)

It should be 1/50th of bank capacity at absorption charging voltage, so for open/non sealed leisures in a 660Ah bank that's 13.2A at 14.4V. Linky:

 

http://jgdarden.com/batteryfaq/carfaq9.htm#charged

 

Maybe see how much Ah can be had from the fully charged bank until the volts start falling off a cliff Then in normal use, and after a full-ish charge, you could use up to half that before recharging.

 

Just an aside, that looks like a quite an expensive install, maybe buying a Smartguage wouldn't add that much to the cost overall.

 

cheers, Pete.

~smpt~

Edited September 20, 2012 by smileypete

[Joshua]

It should be 1/50th of bank capacity at absorption charging voltage, so for open/non sealed leisures in a 660Ah bank that's 13.2A at 14.4V. Linky:

 

http://jgdarden.com/...aq9.htm#charged

 

Maybe see how much Ah can be had from the fully charged bank until the volts start falling off a cliff Then in normal use, and after a full-ish charge, you could use up to half that before recharging.

 

Just an aside, that looks like a quite an expensive install, maybe buying a Smartguage wouldn't add that much to the cost overall.

 

cheers, Pete.

~smpt~

 

Thanks Pete,

 

 

 

 

Just stopped charging (about 10 hours in total, 4 on the generator and 6 on the engine alternator.

 

Just before I shut down, alternator was still on absorption (it is supposed to stay on absorption for 4 hours whatever the state of charge but seems to do this for 6 rather than 4 hours).

 

At that point I had readings of 14.3 for Charge Voltage and an input current of 3.6A.

 

Soon after the Mastervault system switched to float when the monitor suddenly changed readings to 13.2V and 1.4/-0.26A.

 

I would say well and truly charged!

 

Now I am going to try and log my actual consumption based on appliance and time used, god I’m not looking forward to this!

 

By the way, in your earlier post you suggested drawing 33A for 20 hours, that would be 660A, the total capacity of my bank, I am missing something?

 

No problem getting a smartgauge, I will take the advice of the engineer who fitted the system when I see him in November (unless it totally collapses before then!) but to be honest I am not yet sure this is just a question of error readings i.e. faulty shunt or monitor. That doesn’t explain how I end up with such a depleted battery bank after apparently very little demand. A smartgauge wont fix that. I first have to understand what is wrong.

 

 

 

 

Joshua

 

 

[blackrose]

We are due to have a couple of little brackets welded to the boat soon and this will entail disconnecting our batteries...

 

I just had a full size skin tank welded to the inside of my swim. I took off some paint in a couple of places on the uxter plate overhang just above where the tank was being welded in and asked the welder to use these for his earth clamp. The batteries were only about 2ft away on the uxter, and the alternator was just behind the welder.

 

All I did was isolate the batteries and everything was fine. For a couple of little brackets I really wouldn't bother disconnecting the batteries. Anyway, if it did all go wrong, how's disconnecting the batteries going to stop your alternator getting fried?

Edited September 20, 2012 by blackrose

[smileypete]

I would say well and truly charged!

 

Now I am going to try and log my actual consumption based on appliance and time used, god I’m not looking forward to this!

If the batt monitor can read Ah (amp hours), and is reading amps accurately, and everything is going through the batt monitor shunt, then why not use that to measure total consumption in Ah?

 

 

By the way, in your earlier post you suggested drawing 33A for 20 hours, that would be 660A, the total capacity of my bank, I am missing something?

No, you could discharge 80% of that 660Ah and see what happens, but if you can't get anywhere near that then the bank has lost capacity.

 

cheers, Pete.

~smpt~