# Is it the battery or the inverter?



## Ricster (Sep 3, 2010)

We bought a Nikkai 1000w (quasi, not pure - pic) inverter from Maplins for £100. In the van we have a leisure battery - A Moll Solar which has the writing 12v 100Ah(K100) 90Ah(K20) 75Ah(K5) written on the side and I have to admit to my ignorance on this as I don't have a clue what the Kx values are - which is recharged with the alternator. When I check on the habitation panel I can see the power output of both engine and leisure batteries. Both are round about the 12-13v levels.

The issue is when I tried the battery and inverter with our TV/DVD combo (with a DVD playing), which I believe is pulling no more than about 80w, it lasted about an hour before the inverter gave off a set of beeps in sequence, which the instructions indicate is low power. I've repeated this several times and an hour is as much as you'll get before the beeps. What is interesting is that there is a fan on the inverter but it never kicks off. The inverter also has an earth that I did not connect.

I already had a "cannister style" 120w inverter that plugs into the cigarette lighter socket and it can run the same TV/DVD combo for more then 2 and half hours. I've not put it on for longer in fear of flattening the engine battery.

Now the question is, is the leisure battery goosed or am I expecting too much in a 1000w inverter and (what I presume is) a standard battery? The thing that's confusing me is that the power output on the panel shows the same voltage for the leisure battery as it does the engine one and the inverter fan never kicked off.

I realise it's a tricky job making blind suggestions, but what's the gut opinion here? A new leisure battery or should I return the inverter for fixing/replacing with a lower wattage one.

Thanks in advance,
Ric. 

ps: ..and no, sadly I don't have a multimeter


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## Techno100 (May 8, 2010)

I run my TV/DVD from a 150watt inverter so 1000 should be overkill. I'd suspect not enough battery/ies

I get a good few hours from my 2x110AH batteries without signs of caving in and they fill back up from my solars


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## pieterv (Feb 3, 2009)

Hi,

From your description it sound like you have run the 120W inverter from the engine battery, but ran the 1000W one from the leisure battery. So, you are not comparing like for like.

It might well be that the leisure battery is (way) past its best. The fan of the inverter not coming on just indicates that it is not working very hard, which makes sense since you are running a load that the 120W inverter can also manage. 

I think the 1000W will be slightly more wasteful than the 120W, but not massively so. If a 100Ah battery cannot run an 80W load (which might be a 100W due to inefficiency of inverter) for more that an hour it needs replacing.

BTW the voltage of a battery is no indication of its "power".

Pieter


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## Ricster (Sep 3, 2010)

Techno100 said:


> I run my TV/DVD from a 150watt inverter so 1000 should be overkill. I'd suspect not enough battery/ies


I understand the logic, although don't inverters only pull the power necessary? This would maybe explain why the fan on the inverter never kicks off, because it's just not working hard enough for it to be needed.

What I'm looking to run is a laptop, games console and a tv/dvd combo which should come in under the 600w even if they were all in at the same time. I read somewhere that inverters work best when at half power so hence the 1000w decision.


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## cater_racer (May 1, 2005)

An inverter has a quiescent current equivalent to about 3% of its peak rating, so about 30 watts or 2-3 amperes. So your using a sledgehammer to crack a nut. The start-up surge would also be way OTT.

The most efficient way to run an inverter is near the top of its rating, that way they're about 80-90% efficient.

I'd recommend a much smaller one for this application.

HTH

Cater (Ex inverter designer)


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## Ricster (Sep 3, 2010)

pieterv said:


> I think the 1000W will be slightly more wasteful than the 120W, but not massively so. If a 100Ah battery cannot run an 80W load (which might be a 100W due to inefficiency of inverter) for more that an hour it needs replacing.


Cheers, Pieter.

This was sort of the answer I was wanting to hear to be honest. I had half a mind on replacing the battery but wanted to throw it out to the forum.


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## Ricster (Sep 3, 2010)

cater_racer said:


> The most efficient way to run an inverter is near the top of its rating, that way they're about 80-90% efficient.
> 
> I'd recommend a much smaller one for this application.


Interesting.. especially considering your previous job. I think I may be looking at a smaller inverter (300w/600w) as well as a new battery too boot.

Many thanks for the info, I was way off with the suggestion "half power" was ideal.


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## rayc (Jun 3, 2008)

Ricster said:


> I had half a mind on replacing the battery but wanted to throw it out to the forum.


We don't want it


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## pieterv (Feb 3, 2009)

If you intend to run a 600W load you will empty your battery very quickly, even if it is in good shape.

E.g. 600W makes 50A (if the inverter would be a 100% efficient so in practice a bit more).
Running that for 1h half empties an 100Ah battery (and you shouldn't really discharge them much further, or they won't last very long).


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## Jezport (Jun 19, 2008)

Sounds like you need a new battery.


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## kandsservices (Sep 5, 2010)

The fans on most new inverters dont come on unless they are needed to cool it down sounds like your batteries are shot take them to halfords fully charged and they will carry out a battery test on them hope this helps.


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## Ricster (Sep 3, 2010)

Thanks a lot for your answers guys. As we are planning on a fairly lengthy trip, I think we should just invest in a new battery and a smaller inverter (prob 300w).

This leaves me with one final question and that is about charging the battery. If I've been recharging what looks like a 100Ah battery, if I replace that with a new 110Ah (or even higher, 125+) should that still charge as normal?

I realise this is a pain in the ass question to answer without seeing the recharger/setup but in general should a recharger recharge regardless of the Ah the battery is?

Thanks, again, in advance.


Edit: Ooh, and if anyone would like to recommend which battery maker is "the best" then that would be appreciated.


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## geraldandannie (Jun 4, 2006)

You'll be fine with almost any sized battery. We have 2 X 110Ahr leisure batteries, and use the standard charger.

Also, I'd go along with cater-racer's thoughts earlier. An inverter is its most efficient operating at near to its full rating. With a 1000W inverter delivering 80W, you'll be gobbling up a load of current just to operate it.

Have a look at the following graph.










Gerald


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## Techno100 (May 8, 2010)

Good quality sealed battery at a good price delivered


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## Ricster (Sep 3, 2010)

Heh.. yeh, when looking about these forums you tend to get a mixed bunch of answer on loads of topics, but when a lad who used to design inverters gives you the low-down, you're best to listen..


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## kandsservices (Sep 5, 2010)

dont forget your batteries are only charged upto about 85% of its capacity when being charged via your charge unit thats fitted you should remove your batteries about every three months and charge them with a proper battery charger.


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## Jezport (Jun 19, 2008)

kandsservices said:


> dont forget your batteries are only charged upto about 85% of its capacity when being charged via your charge unit thats fitted you should remove your batteries about every three months and charge them with a proper battery charger.


Never heard that one, please elaborate.


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## Techno100 (May 8, 2010)

Jezport said:


> kandsservices said:
> 
> 
> > dont forget your batteries are only charged upto about 85% of its capacity when being charged via your charge unit thats fitted you should remove your batteries about every three months and charge them with a proper battery charger.
> ...


Me niether, the battery should take all it needs.


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## erneboy (Feb 8, 2007)

The OP said, "In the van we have a leisure battery - A Moll Solar which has the writing 12v 100Ah(K100) 90Ah(K20) 75Ah(K5) written on the side............ ."

I may be wrong but that looks like information for three different batteries all fitted into the same casing. The K100 is 100Ah, the K20 is 90Ah and the K5 is 75Ah. If so there should be further identification telling you which version yours is. It makes a difference to knowing what you should expect from the battery. The Moll Solar web site didn't help much.

I may be wrong, Alan.


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## Patrick_Phillips (Aug 17, 2006)

Ricster said:


> A Moll Solar which has the writing 12v 100Ah(K100) 90Ah(K20) 75Ah(K5) written on the side and I have to admit to my ignorance on this as I don't have a clue what the Kx values are


As I understand it, the K numbers are the rate of discharge at which the Ah rating is calculated.
The battery will deliver 100 amps for 1 hour. If you take only 20 amps, the battery will deliver for 90/20 hours or 4.5 hours making a total of 90 amps. Take just 5 amps and the same battery will deliver only 75 amps over the period of discharge before becoming unusable.
If you want high cranking power, look for the rating at K100. If, on the other hand, you want to maintain a low wattage for as long as possible look for a high K5 rating.
Maybe this site explains it better: http://www.dcbattery.com/faq.html

On another thought, wherever you can, use 12v equipment rather than mains voltage stuff. It will get you better service from your available battery storage. This includes the laptops. Look at using 12v laptop power supplies. Maplins sell them, amongst others.

Patrick

Edited: Please note that I am officially ga-ga. The K measure is of course time not amps as posted by Davidcampervanstuff. The principle holds but best disregard my attempted explanation.


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## davidcampervanstuff (Nov 24, 2007)

erneboy said:


> The OP said, "In the van we have a leisure battery - A Moll Solar which has the writing 12v 100Ah(K100) 90Ah(K20) 75Ah(K5) written on the side............ ."
> 
> I may be wrong but that looks like information for three different batteries all fitted into the same casing. The K100 is 100Ah, the K20 is 90Ah and the K5 is 75Ah. If so there should be further identification telling you which version yours is. It makes a difference to knowing what you should expect from the battery. The Moll Solar web site didn't help much.
> 
> I may be wrong, Alan.


The faster (larger load) you take current from a battery, the less is its effective capacity. Battery manufacturers ideally label their products with its capacity at different discharge rates eg if you discharge it over 20 hours, or much faster over just 5 hours.

It has been common for this information to be missing from the labels (and I think often difficult to discover by other means) but there are now new EU regulations in effect which, over an introductory period, should see all batteries labelled with capacity at three discharge rates. The label on yours indicates that the battery is rated at 100Ah when discharged over 100 hours, 90Ah over 20 hours and 75Ah over 5 hours.

David


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## erneboy (Feb 8, 2007)

Thanks for that explanation. I knew that was what happened but I didn't consider the possibility that labeling would explain the performance of individual batteries. 

I learn something new every day, it hasn't been a wasted day, Alan.


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## Ricster (Sep 3, 2010)

Just to clarify the end result for us. We bought a new leisure battery (the Numax on suggested in an earlier post) and a much lower capacity inverter (Silverline 300W). All is now ginger peachy, with uninterrupted power for hours on end.


Many thanks to all who contributed to this thread.


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## Techno100 (May 8, 2010)

Thanks are conveyed by use of the "Thank" tab at the top right of each post. Glad you're sorted.
Andy


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