Power Drawn By An Older Inverter

[cheshire~rose]

I do realise I am about to open a right old can of worms by posting an electrical question when I have no knowledge at all of anything electrical but here goes!

 

We have had a fault on the boat where the batteries have not been lasting as long as they should have done. The batteries (1 year old) have been tested and deemed to be ok. A fault was found this weekend with the isolator switch. It seems we were losing a volt with the faulty switch and this was replaced. The switch that was replaced was one in the engine bay which you would use to isolate EVERYTHING if you were leaving the boat somewhere random. Usually our boat is left on it's marina mooring hooked up to mains power to keep the batteries topped up. We do not generally use the main isolation switch when we are on our home mooring but instead switch off all the individual circuit switches on the panel inside the boat.

 

We have not had any opportunity to test is the system works any better now but I do not expect the replacement of a switch we hardly ever use to make any difference to how long the batteries last when in use.

 

We were told there is a strong likelihood that our inverter (which is probably around 8 years old) is now drawing too much power when in use. My understanding of the way it's possible behaviour was described is that the a micro switch inside the unit detects a demand for power and so draws it from the batteries to supply it to where the demand is. With age it is losing it's ability to detect the different levels of power demand and so draws much more from the batteries than is being demanded by the item(s) we have plugged in.

 

My first question is; do those who have a better understanding of electrickery than me think that is a resonable suggestion of where our power may be vanishing to?

 

My second question: Is our inverter likely to fail spectacularly some time soon if this suggestion is correct. If so should we be wary of continuiing to use it?

[GUMPY]

The explanation to me does not make sense.

Current draw depends on the make and model of the inverter, some even 15 years ago were better tnan those on sale today.

[pistnbroke]

If your main isolator switch was causing a drop of 1v then yes it will make a big difference. Ocasionally operate the switch as this will help keep the contacts clean.

I think you are being told rubbish about your inverter ...microswitch ??? total load of bullshit....If your inverter is working /powering your loads fine ,not over heating or blowing its fusing then its fine.The only place power can disapear to is heat ..... Bet the person who told you this sells them .

 

I suggest you dump the person who is your electrical advisor

Edited May 28, 2013 by pistnbroke

[nicknorman]

Seconded (or thirded) - the only thing that needs replacing is your electrical advisor. Why not spend £30 on a DC clamp meter and then you could see what current is going where - it might help to de-mystify things.

[cheshire~rose]

Thanks for your replies everyone. We need to use her a while to see what effect the new switch has had upon the situation.

Seconded (or thirded) - the only thing that needs replacing is your electrical advisor. Why not spend £30 on a DC clamp meter and then you could see what current is going where - it might help to de-mystify things.

 

We have one - you can clamp the little clips onto things that are to do with electrical current and depending where you clamp them you get different readings. The novelty of making it read different things wears off when you you have no idea what the readings mean!

 

I understand the mechanical stuff but electrics make a whooshing noise when the details enter one ear and do a quick circuit of the area most people keep their brain before leaving by the other ear. Dave can do some basic stuff like installing the radio etc but he does not like messing with electrics and so has never really tried to get an understanding of it.

 

Allan AKA Keeping-up made a few suggestions of some basic tests we could do ourselves before paying for someone to test anything. In his usual manner he spent a long time carefully writing it all into an email that even I could understand (bless!)

 

I printed the email out and we got the tester gizmo out of it's nice box (unsure if it has ever been out of the box before!) The plan was I read out the email as Dave did the tests and I recorded the results.

 

Allan wrote "Open the switch" - Dave looked at me and I looked at him, does he mean switch it on or switch it off? Well I said, if you open a tap then you switch it on to allow water through so I would say switch it on to allow current through. Ah said Dave, but if you open a set of contacts you stop allowing current through so that would mean switching it off. (Yes we now know it meant switch it off!)

 

At this point we were uncertain, if we carried out the tests with a switch on when it should be off we could blow something up. If we did it with a switch off when it should be on we would not get the expected results. We shrugged our shoulders and took her to the boatyard!

 

We will give her some use and hope that things settle down.

[nicknorman]

I think you have electrophobia. A bit like my arachnophobia when i see a large spider! Irrational, but powerful!

 

Anyway, if your master switch was losing a volt, this would give the symptoms of prematurely flat battery so you might find its better now.

[pistnbroke]

Personally Ive never seen a flat battery ..is that when its been run over by a truck? All mine stay brick shaped even when discharged

[alan_fincher]

We were told there is a strong likelihood that our inverter (which is probably around 8 years old) is now drawing too much power when in use. My understanding of the way it's possible behaviour was described is that the a micro switch inside the unit detects a demand for power and so draws it from the batteries to supply it to where the demand is. With age it is losing it's ability to detect the different levels of power demand and so draws much more from the batteries than is being demanded by the item(s) we have plugged in.

 

 

The explanation to me does not make sense.

Current draw depends on the make and model of the inverter, some even 15 years ago were better tnan those on sale today.

 

 

I suggest you dump the person who is your electrical advisor

 

 

Seconded (or thirded) - the only thing that needs replacing is your electrical advisor. Why not spend £30 on a DC clamp meter and then you could see what current is going where - it might help to de-mystify things.

 

"Fourthed" - Your advisor is in my opinion talking "danglies", and should be avoided...............

[bottle]

True

 

but

 

tell any non battery officienado that the battery is discharged, 10 to 1 they will not know what that means, tell them it is flat and they will then know what you are talking about

 

Edit: Alan jumped in while I was typing.

Edited May 28, 2013 by bottle

[alan_fincher]

Actually just re-reading your first post.......

 

Although not in the position ourselves of using a float charger to keep batteries topped up, I guess I'm kind of surprised that you leave the boat with its main isolator connected, relying instead on individual switches.

 

To me the purpose of a "big switch" is to guarantee isolation of the batteries from everything else, and hence peace of mind when you are not there. (Although if you have an autmatic bilge pump, that is one thing I would expect it not to isolate).

 

Perhaps in my naivety I would have expected any float charging arrangement not to require the isolator left connected, but perhaps I'm wrong about that - could those electrically savvy people familiar with such arrangements please comment?

[NB Alnwick]

I realise that this may be seen as a blatant advertisement - but we solved almost all of our inverter/battery problems by installing a 'Smartgauge' - on the advice of forum members (mostly Gibbo), we did rewire our battery bank in a more sensible fashion with heavier gauge wiring at the same time.

 

Looking back, I do not know how we coped beforehand - nowadays we never allow our batteries to get too heavily discharged - usually keeping them above 75% and rarely letting them go down to less than 55%. It has made a huge difference.

 

Finally, we always switch off the main isolating switches before leaving the boat for any length of time. I think this is a sensible precaution and it does help to conserve the batteries - 'Alnwick' needs a lot of battery grunt to wind up the K3.

[nicknorman]

Our charging is through the Combi, which is only fused and not via an isolator. However not sure this is optimal. Whatever, we leave the mechanical master switch on, just turning off the Empirbus master which is configured to leave power on to the bilge pump, Mikuni and GSM remote control.

 

Provided you remember to turn everything off, I don't see a need to turn them off twice by opening the isolator.

[RLWP]

The details of your inverter should be in the boat manual that Dave guards so well. The technical section should give you the current draw

 

Richard

[OldGoat]

_Gentlemen,

_{are we, perhaps, not missing what the OP is trying to say?}

_{My interpretation (ignoring the voltage drop) is that the inverter is left on 24/7 and its standing current is consuming power?}

 

_{I have an aged Stirling unit and I recall it draws 450mA in idle. This unit has a remote control which I always turn off when not in use. I have no idea what the standing current then is.}

 

_{So the short answer is - If you leave your inverter "ready for use" for long periods, then the batteries will go flat.}

[cheshire~rose]

_Gentlemen,

_{are we, perhaps, not missing what the OP is trying to say?}

_{My interpretation (ignoring the voltage drop) is that the inverter is left on 24/7 and its standing current is consuming power?}

 

Apologies but in this case your interpretation is incorrect. I suspect many of the people who have posted replies know more about our use of the boat than I gave imformation about in my opening post.

 

We are leisure boaters and often only manage to get to the boat once a month (although do our best to spend as much time there as possible)

 

The inverter is only switched on when it is required to power something.

[alan_fincher]

Depending on the quality of the isolator switch that you say was displaying a volts drop, I would even deign to suggest that it is possible, (but I'm not suggesting by any means certain!), that the fact it isn't switched fairly regularly could be part of the problem. To some extent some heavy duty switch contacts actually benefit by the action of being turned on and off from time to time, particularly if it results in one contact sliding over another, and clearing any build up of surface "grunge", (a technical term!).

 

A high current switch that is seldom switched can end up being a problem switch, in my experience.

[cheshire~rose]

Depending on the quality of the isolator switch that you say was displaying a volts drop, I would even deign to suggest that it is possible, (but I'm not suggesting by any means certain!), that the fact it isn't switched fairly regularly could be part of the problem. To some extent some heavy duty switch contacts actually benefit by the action of being turned on and off from time to time, particularly if it results in one contact sliding over another, and clearing any build up of surface "grunge", (a technical term!).

 

A high current switch that is seldom switched can end up being a problem switch, in my experience.

 

Acknowleded - this was mentioned in post 3. I did not even know the switch existed until this weekend but when I read post 3 I thought even if you decide not to isolate when we leave the boat it would not hurt to get into the habit of switching the switch when we grease the stern tube just to keep it free.

[Timleech]

When you say the inverter is only switched on when required, is that via the inverter switch or a master switch in the supply?

AIUI they will generally draw some current when connected even if 'switched off'. It might not be much, but may be enough to matter when the boat is not in use.

 

Tim

[jonathanA]

When you say the inverter is only switched on when required, is that via the inverter switch or a master switch in the supply?

AIUI they will generally draw some current when connected even if 'switched off'. It might not be much, but may be enough to matter when the boat is not in use.

 

Tim

err the OP says they are on a landline to keep the batteries topped up so the small draw of the inverter (off off or off standby) shouldn't be a problem.

 

out on the water they only switch on when needed so even if this uses the remote control option and there is a small residual draw it would be a few milliamps so again should not be an issue.

 

The big mistake most people make in diagnosing any problem is changing too many things at once. The master isolator has been changed so has that fixed the problem ? if yes then great (and if you were being really anal you'd put the old one back in to see if the fault re-appeared but not many people would deem that worthwhile)

 

I'd be a bit cautious about leaving the master isolator off (in the marina) unless I knew that the charger bypassed the isolator.

[Keeping Up]

The isolator switch replacement will make a huge difference.

 

FWIW when on its mooring I always leave the boat with the master switch ON (yes that's closed, Rose) but all the domestic electrics switched off by a domestic master-switch inside the boat. In that way the battery charger float-charges the battery, in the same way as you describe. This also means the inverter is switched off when the boat is left moored up.

 

All inverters take a certain amount of current from the 12v supply, all the time that they are switched on - even when they have no load on their 240v output. This is often called the standing current, or standby current. Some older inverters actually have a lower standing current than some brand new ones; it is possible but highly unlikely that this current can increase with age, but it is easy to measure. Then they waste a bit more electricity when powering a load - this is their conversion efficiency - and an older inverter is likely to be slightly less efficient than a newer one; again it is possible but unlikely that the efficiency will worsen with age. Typical values are between 0.5 and 2 amps for the standing current, and 85%-95% for the conversion efficiency (the overall efficiency is the combined effect of these two features and will therefore vary according to the amount of 240v load.

 

I would not recommend doing anything different with your inverter until you have observed the effect of the new isolator switch, and then (if necessary) dig out my page of instructions and, with your new knowledge of the meaning of the terms open and closed, try the tests again.

[cheshire~rose]

Thanks again for your advice and assistance everyone. I think we are feeling a little more confident about our inverter thanks to your valuable input. Thanks for taking the time to decribe things in terms that someone with electrophobia can take in.

 

I think the one thing that was niggling at the back of Dave's mind was that the place we took the boat to test for the fault was the place that supplied the batteries which we thought had a potential fault. The drop test they had done suggested they are fine but lot's of people seem to be having batteries failing prematurely recently and a drop test does not always show the fault.

 

So they found a faulty isolator switch and replaced it. my thought was that although the switch was faulty, it was tested and found to be faulty in the off position which is a position it is not usually in. So would it have been losing current in the "on" position? I know it is possible because it was an old switch and if the contacts were as mucky as most of the rest of the engine hole then there was all sorts of crud which could have been conducting power to places it should not have been.

 

We were just a bit concerned that the isolator switch with the mention of a potential of an inverter problem was a smokescreen to put us off the scent of a duff set of batteries - let us wait and see what happens before we start changing anything else.

 

Thanks again

[Keeping Up]

The switch could be "losing current" in the off position, and slowly draining your batteries if you had left something (such as a light or the inverter or fridge) switched on while you were away from the boat, relying on the isolator to switch them off, and not using a battery charger. But I don't think this would apply in your case?

 

On the other hand in the on position it could be losing you volts rather than current. If it lost you 1 volt for example this would mean that if your batteries had 12v, the boat would only be getting 11 of them and therefore it would look as if the batteries were flat when they weren't. But slightly more obliquely, if your alternator was putting out 14v it would mean that the batteries would only get 13 of them. This would mean that they weren't getting properly charged which would not only add to your problems but would also result in them becoming "sulphated" which means they would have a permanently reduced capacity (which may or may not show up on a drop test)

[larkshall]

Well I would agree that the isolator switch could be the problem, and as others have said switvhing it on/off once is a while is a good idea. (I had one fail (415v 3 phase job) when needed in a hurry, it jammed on, not funny caused a small fire) Lesson learnt, operate switch monthly at least !.

 

I doubt you have any problem with the inverter, yer leccy sage, is talking out of his/her fundament. inverters tend to be go/no-go.

 

If you are going to turn off when leaving the boat (A good idea in principle), do ensure bilge pump is not affected.

[cheshire~rose]

Just to update on this issue. We have Clive Penny (Marine Electrician) come out to the boat yesterday. He spent a couple of hours checking things over and testing what he could and he has confirmed that the inverter appears to be working as he would expect and he is 99.9% certain that our batteries are fine.

 

I was a little dismayed when he described our shore power set up as "quaint" but I now realise that "quaint" also means it is simple and so there is less to go wrong

 

There is definately something we are running which is drawing more power than it used to and he suggested two routes towards working out what it is.

The first is the cheap and not technical way - to spend time switching off each suspect item and seeing what effect that has on how long our power lasts

The second would be to fit a smart gauge and he has quoted me for doing so.

 

The biggest suspect is the fridge - being 9 years old it is at a suspect age and fridges can carry on for years just getting less and less efficient. As I have to keep it on it's lowest setting to stop it from freezing the contents I had already suspected it of being a potential culprit but what do I know!

 

Of course Dave would like a nice shiny smart gauge gadget to monitor everything but in truth we have managed without one so far and as we may have to spend out a lot of dosh on a new fridge I would rather wait. We have 2 weeks away on board starting next weekend and so we can have the fridge on when we chug and switch it off when we stop and that will soon tell us if it is the fridge that is our problem.

 

Oh and before anyone suggests it I pulled the fridge out yesterday and vacuumed behind it. I was expecting it to be a lot more dusty than it was so at least I know it is not my idleness at cleaning behind there that has caused a problem

[Timleech]

There is a middle way, which is to fit an ammeter and watch what it tells you while you switch things on and off.

Cheaper to buy than a Smartgauge, but if you're paying to have it fitted the fitting cost is probably similar or a bit greater.

 

Tim

Edit - can the warm air from behind the fridge circulate and escape freely?

Edited July 12, 2013 by Timleech