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Do inverters become less efficient with age?


Obone

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Do inverters become less efficient with age?

 

we typically spend two to three weeks away cruising in the NW, on average charging for five hours. At rest in the evening or moored during the day with the inverter switched off, the voltage stays steady in the high 12 volts.

 

When we switch on the inverter the voltage falls to below 12 volts in under two hours. Admittedly we only have the inverter on for TV (we know not to use hair driers, vacuums, washing machines etc without running the engine).

 

Is this indicative of aging batteries (bank of four deep cycle batteries- probably over five years old), or might it be a faulty inverter? Or should I just buy a 12v TV?

 

owen7

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2 minutes ago, Obone said:

Do inverters become less efficient with age?

 

 

No, but batteries do.

 

This is almost certainly a battery problem. May I refer you back to the first post in this thread? 

 

Welcome to the forum by the way :) 

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4 minutes ago, Obone said:

Thank you for your swift response.

I’ll buy a 12v TV. Cheaper than four new batteries.

If you batteries are goosed a 12 volt TV will still run them down. Is your  inverter a cheapy that uses lots of leccy things to power it?

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Buying a 12v TV may give you and extra few minutes but it sounds like the batteries are 'dead'.

From the basic information provided it appears you need to replace your battery bank.

 

A quick & dirty way to check battery capacity :

1) Switch everything off.

2) Take a battery voltage reading ( a couple of hours after switching off the charger) you are looking for 12.8 (ish) volts

3) Connect a known load (maybe a 55 watt headlight bulb, 12 volt fan etc etc)

4) Run it until the battery voltage is down to around 12.1 - 12.2 volts.

 

How long did it take ?

You can then work out the number of AH used, multiply by 2 and you have a VERY rough idea of the battery capacity.

5 minutes ago, ianali said:

That’s it. Easy solution isn’t it. 

And when that stops working, just buy a 6v TV

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As the OP has declined to answer the questions in post 1, he is probably doomed to buy new batteries every 18 months for ever. Or more frequently. 

 

I get the feeling we have given the wrong answer. We are all supposed to be saying yes inverters wear out, buy a new one and everything will be fine! 

  • Greenie 1
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I am genuinely appreciative of your initial response, and it confirms our suspicions. 

I will hopefully be able to complete the checklist from v1 tomorrow and get back to you then.

Sometimes real life gets in the way of my boating.

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A TV used in the evening  (in general) consumes relatively little power, but that assumes a 24" set (some folks have large tvs and they do consume much more), thus as in most things "it all depends" OTOH a 12v fridge consumes a lot more and it will be consuming power for some time during a 24 hour period.  

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The 12v fridge doesn’t seem to dent the battery at all during our days moored up, even when it is hot as it has been in the last few days. This is partly why the inverter come under suspicion.

 

Small TV are all we need by the way. 

 

Thanks for for your response 

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1 hour ago, Obone said:

I am genuinely appreciative of your initial response, and it confirms our suspicions. 

I will hopefully be able to complete the checklist from v1 tomorrow and get back to you then.

Sometimes real life gets in the way of my boating.

 

To be fir it is not an easy list of questions to answer, but all battery threads end up asking all the questions so the board can get a clear understanding of your system. If the answers arrive in dribs and drabs it takes FAR longer to arrive at a proper diagnosis. 

 

 

15 minutes ago, Obone said:

The 12v fridge doesn’t seem to dent the battery at all during our days moored up, even when it is hot as it has been in the last few days. This is partly why the inverter come under suspicion.

 

I suspect it does actually, but this doesn't show up until you turn the inverter on late in the day, when the fridge has heavily drained the batts and the inverter is the first to complain.

 

Do you have a clamp meter that measures DC current? And/or a digital multi meter?

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Are you sure the inverter is only powering the tv, not something else left on? Immersion heater etc. It doesn’t sound as though you have any battery monitoring equipment and, with electricity being invisible, this means you have no idea what’s going on!

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1 hour ago, Obone said:

I have based my observations on a voltage output digital reading, which I assume averages the four domestic battery output.

Digital reading from what instrument? This winter I fitted a 50mm digital voltmeter in place of the analogue one and I am sure its reading 0.2 to 0.3 volt low. If its on an Ebay bargain I would want to double check t with a decent multimeter.

 

We normally measure battery output in Amps or perhaps Amp Hours, not volts but if you mean is the voltage you read the average across the bank of four batteries then the answer is yes with them all connected in parallel but it you measured them disconnected individually you might find one or more faulty ones are at a lower voltage because the good ones will not be trying to charge it and holding the voltage up.

 

You could well have one or more batteries with shorting cells.

 

 

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1 hour ago, Obone said:

I should add that there is no other 230v draw on the inverter.

 

That's a very bold assumption to be making.

 

If it is not an assumption, how are you measuring the draw on the inverter?

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2 hours ago, Obone said:

I have based my observations on a voltage output digital reading, which I assume averages the four domestic battery output.

The batteries are all connected together in parallel which means their voltages will be (near as dammit) identical. However apart from the points above about accuracy, a voltmeter has limited use since the voltage of a battery is not directly related to its state of charge. Yes SoC can be determined by voltage, but only when the batteries are not passing any current and have been in that state for a while. But more importantly, a voltmeter won’t tell you WHY the batteries are in the state of charge they are, and of course this is the very question you are asking and we can’t answer (because we and you don’t have the information). We don’t know if the problem is low capacity of the batteries or something (inverter suspected) taking a lot of current. Without current and preferably charge monitoring, we are all in the dark (as you will literally be soon!)

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No doubt this fact will open me to howls of derision from all but it may help. Due to work commitments and the electric system set up the batteries were left isolated over the winter, with no charging or load attached (I know this is not ideal). On our return the battery voltage read out showed 12.2v. 

I also understand that voltage is not a direct indicator of battery SoC. Is instrumentation available hat can measure SoC?

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19 hours ago, OldGoat said:

A TV used in the evening  (in general) consumes relatively little power, but that assumes a 24" set (some folks have large tvs and they do consume much more), thus as in most things "it all depends" OTOH a 12v fridge consumes a lot more and it will be consuming power for some time during a 24 hour period.  

Blimey! even 24" is large for a boat, in my book. How do you get far enough away to view the whole picture -- TV at one end of the boat, sofa at the other?

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4 minutes ago, Obone said:

No doubt this fact will open me to howls of derision from all but it may help. Due to work commitments and the electric system set up the batteries were left isolated over the winter, with no charging or load attached (I know this is not ideal). On our return the battery voltage read out showed 12.2v. 

 

No howls, this is very helpful info which probably explains a lot. Your batts are probably very sulphated as this isn't 'not ideal' it is fatal to lead acid batteries! 

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1 hour ago, Obone said:

On our return the battery voltage read out showed 12.2v. 

I also understand that voltage is not a direct indicator of battery SoC. Is instrumentation available hat can measure SoC?

Having been fully rested you can indeed use that voltage as an indicator of SoC. They’re at approximately 50%. However, their capacity will no doubt be shot, as Mike posted. So if they were 110Ah Batteries they are now likely to be 50Ah Batteries (if you’re lucky).  

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1 hour ago, Machpoint005 said:

Blimey! even 24" is large for a boat, in my book. How do you get far enough away to view the whole picture -- TV at one end of the boat, sofa at the other?

If you watch TV across the width of the boat - and it would appear that many do, then I would agree with you, but we have a dinette, so the box is 8ft plus away from us.

FWIW it's cantilevered out from the wall and folded flush when not in use.

I did see a comment on here some time ago that some folks have 50" TVs on their boats.....

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Although it seems that the batteries are more than likely goosed I have the information as requested in v1.

 

1. Sealed deep cycle batteries

2. 4 off Numax CXV XV31MF (110Ah). They are at least four years old.

3. Battery voltage is monitored using a three digital digital read out. No obvious make but does have code YB27-V14 on PCB.

4. Batteries are charged by an engine driven alternator when underway, and via a mains supply through the inverter combi unit whilst in Marina.

5. Alternator 80A/12v HMI model number 900021-ALS (standard fit in Isuzu engines)

6. Measured charging voltage 14.37v

7/8. Underway the batteries are charged continuously by the alternator. Voltage initially rises to high 12volts ending the day above 14 volts. When moored voltage is monitored using the digital read out described above. When it falls below 12v we start the engine or turn off the inverter. When in the Marina the charging is carried out via the inverter combi unit (Sterling Pro Combi S). This unit will only charge the batteries if also operating as an inverter. It does not have a stand alone charging facility, hence why the batteries were not charged over the winter.

9. I believe the combi unit monitors the voltage and maintains charge on ‘float’ after initial charge. Whilst motoring there is no such monitoring control the alternator output.

10. Underperformance as previously described.

 

recommendation for improvements to battery regime gladly received, as would recommendations for system/instrumentation upgrades.

 

owen

 

 

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The most important thing with lead acid batteries is to fully charge them routinely. When a lead acid battery isn’t fully charged, a process called sulphation takes place. This is partially, but not completely, reversible. Routine sulphation leads to permanent irreversible sulphation and that means significant to massive loss of capacity.

 

You cannot tell when the batteries are fully charged by looking at the voltage during charge. So when you mention that the voltage reaches 14.37 towards the end of the charge, well when it reaches that voltage the batteries are still a long way to being fully charged. Unfortunately batteries are annoying things that much longer to go from say 90% State of Charge to 100% SoC than they do to go from 50% to 60%. So when the voltage reaches 14.37 probably this needs to be maintained for many hours to fully charge the batteries. But you, and we, don’t know!

 

The only practical way to know that the batteries are fully charged is either to leave them on the mains charger for a long time, or to monitor the charging current - which will gradually decrease as the SoC approaches 100%. Once the current is down to say 1% of the batteries’ capacity in AH, it can be considered fully charged. This takes a long time, quite possibly more than the 5 hours you mention. But we don’t know, because there is no current monitoring!

 

 

Edited by nicknorman
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