Battery capacity question

The reason for the question is that once the inverter cuts out the battery voltage will start to recover towards the "rested" reading but if your reading is immediately after it has switched off then it would not have fallen very much lower.

I have looked at the specs on the current Vetus inverters and they all seem to cut out at 20 volts. I would be very surprised if yours is spec'd to cut out at 24 volts. With a big load it would soon be cutting out if that was the case and there is no reason to suppose your inverter/ charger is substantially different to the current straight forward inverters in that respect. Only reference to a manual or advice from Vetus can confirm that though.

That leaves two possibilities.

Firstly that there is a poor connection between the battery and the inverter so that the volts at the inverter input are lower than the battery volts. With the small current that you will be drawing for 100watts that does not seem to be very likely.

Secondly that it is cutting out at the wrong voltage. Ie that the inverter is faulty.

Another possiblity that could be confusing the whole issue is that your voltmeter is incorrect but if you start off with a charged and rested battery reading around 12.7 volts that is more or less ruled out.
 
You should be getting 28 hrs (theoretically). Allowing for the buggeration factor, say 24hrs.

Three questions.
1st. (the daft one) You haven't got anything else switched on. Lights, fridge, instruments etc etc?

2nd. Are you sure the batteries are fully charged? I'm not sure if you have mentioned the starting voltage or not.

3rd. Once it has cut out how long does it take to recharge and do you know roughly what the charging current is?
 
Vic. Many thanks for the time you have spent on this problem. You've certainly increased my understanding in the process. Time to refer to Messrs Vetus methinks
 
Log-in. I'd be more than happy with 24 hours (this is what I got in the previous boat with a very similar set-up but with a Victron charger/inverter) but as I say, I'm getting a quarter of that. As to your specific queries

1. The only other things switched on are the depth sounder and the speed log. For some reason they seem to be wired to be permanently on ( via a fused link)

2. I've measured 25.6 volts on the domestic supply before switching on the inverter and assumed the batteries to be fully charged.

3. Don't know*. Once the inverter has cut out, we've sort of shrugged our shoulders, said 'Ah well' and left it at that. As I said, the boat is new to me this season so I'm still trying to find my way with it. What I do know is if I fire up the main engine, the inverter starts to work immediately. But then I suppose it would, wouldn't it.

Many thanks for your input. Any other ideas gratefully received.

* after a few hours motoring the following day (we are 'continuously cruising') the inverter is ready to deliver the same limited service. Charging is via the engines 80Amp altenator.
 
Batteries sound OK. I don't like the idea of permanently wired instruments but that is completely irrelevant to this problem!

1. Have you checked the battery to inverter connections as Vic has already mentioned?

2. Do you have any battery monitoring dials/guages on board?
(So that you can see what current is being used when the inverter is on).

3. Do you have anything else on board that you could plug in instead of the TV? A light with a 100watt bulb would be ideal, though I doubt that you have one on board.(Try this instead. If it works OK for a longer time then the fault could be with your TV. You would need to know what current the alternative takes.) Unlikely, but easy to check.

4. Do you have a chartplotter/radar on board. Sometimes you can get the battery voltage reading from these, (I bet you need to use the handbook to check this!). This would give you a check against your meter. If they both read the same then........well it's obvious.

....but it is beginning to sound as if it might be the inverter /forums/images/graemlins/frown.gif
 
Bit worried about some rather optimistic battery figures beiong quoted.
I have always worked on the premise that batteries will rarely charge above around 85% and ideally should not be discharged below around 50%. That gives about 35% useable capacity.

Using 2 x 235Ah (12V) batteries in series to give 24v would only give 235Ah capacity so 35% = around 80Ah useable?


A 2Kw inverter will only be about 90% effficient at best so that will use some amps for itself. Running a 2Kw inverter for the relatively modest needs of a TV etc is way OTT IMHO. I have a seperate 300W inverter I use for routine low demand devices like TV/laptop/lights etc. Has the advantage that it only draws a few miiliamps when not actually supplying any appliances whereas my 1Kw inverter turns itself off if there is no demand - in fact I hardly ever use it.

I have 4 x 110Ah 12v batts in parallel for my 12v system and can sit alongside for up to three days without needing to run engines or need shore power and that includes running a fridge 24/7.
2 x 235v in series seems on the low side to me.
 
Yes, but we are simply trying to help OP sort out his problem and the ball park figures are perfectly OK for that purpose. We could go into the minutiae of the physics involved but it won't alter the fact that something is wrong and it needs to be sorted out.

The inverter may be a little OTT but, at this stage, all he wants to do is to get his TV working properly.

Let's not over complicate it, eh?

(FWIW OP's battery set up is bigger than yours. His is operating at 24 volts, yours at 12volts. The total power output from his will exceed yours. Nothing wrong with that but you are misleading him by telling him he ain't got enough batteries.)
 
235 Ah at 24 volts. thats the point. At 24 volts equipment only takes half the current for the same power that 12 equipment takes. So thats makes the equivalent at 12 volt 470 Ah. Marginally more than 4 x110Ah in parallel.

I had not thought about it before but for a given collection of batteries you have the same amount of energy stored or available regardless of how you connect them!
 
You're right of course, so Pherans useable battery capacity is roughly similar to mine and my comment re him being light on capacity was wrong.

However, at 24v a 2Kw inverter under full load will draw around 83 amps and even under light load could be creating a significant drain?
 
Sorry for the spasmodic replies - as I said, we're on the move and it all depends whether and when I can pick up a wi-fi connection. I can't help feeling that you and VicS have correctly identified this as an inverter problem with the cut-out voltage set too high. Whether this is adjustable or not I don't know but I am contacting Vetus for advice. Since the model number of the inverter/charger doesn't seem to be anywhere on the unit itself or the remote control, I have had to send them photographs as an aid to identification. I'll try to remember to get back to you if/when Vetus come up with an answer. In the meantime, many thanks to you and Vic for your help.

Pheran
 
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