The Camping Forum

[nutgone]

I'm gona have to look into this inverter earth scenario, I'm pretty sure what I said earlier was right, but it bothers me that mine has no earth whatsoever, whereas my dad's one (only 150w, with no cooling fan at all) has the earth tag on the socket connected to the metal casing via a ring terminal, even though the metal casing isn't connected to anything else at all (I think).

Think I'll be taking my dad's inverter apart again tomorrow, & looking it up somewhere.

I'm pretty sure isolation transformers don't require an earth & specifically tell you not to introduce one. So, unless you get a direct shock between poles (IE you make the circuit yourself) you shouldn't actually get a shock from just one of them.

I had this trouble getting my head around high impeedance earths required on some generating sets, which is a similar thing.
I spoke to my dad about it, but lost him somewhere near the beginning

[nutgone]

Found this little gem on an Australian website, which kind of backs up my theory on earthing....

No, don't earth it.
Earthing means connecting one output wire to either an earth stake or the chassis or both.
Earthing an inverter output increases the risk of electrocution.

If it's earthed and you touch the wrong (hot) wire, your muscles might respond violently under 'un'favourable conditions.

If it's not grounded you only can get zapped if you touch both wires at the same time (which is true for grounded as well of course). If you only touch one of either wire, nothing will happen to you.

Earthing only is good for distribution grids because it ties the system to earth potential. If this wasn't done, active and neutral could both 'float' to unpredictable voltage levels due to atmospheric charges accumulating in the overhead wires.

Best of luck, mr.batteryvalue

I'll carry on looking, but I really want to be testing!

Trouble is, it's pelting down out there! Not great inverter testing weather

[subaqua]

correct nutgone. the inverter is acting as an isolating transformer. another reason an RCD is an expensive waste of money on an inverter output. especially f its a modified sine wave output as the RCD needs to be capable of discriminating between circulating DC and AC currents .

but its sunday and i really don't want to think about work on a sunday evening

[nutgone]

I went to make a start on this today. although I've had a little car trouble (top hose decided to detach itself from the rad whilst I was blasting up a dual carriageway ).

I've left my inverter croc-clip leads at my brother's place (with all my camping gear) & my multimeter is showing low battery!

Typical!

Well, my "other" tent (the one I bought accidentally) should arrive at my brother's tomorrow, so I'll pop over (just to get my leads mum) & kill 2 birds. I needed to give the car a good run out anyway. Just make sure I take some tools & plenty of water with me, just in case.

[nutgone]

Here we go folks, the first set of results are now in......

I started with an 85Amp/hr leisure battery, the preliminary voltage reading was around 12.5v, so I put it on charge for a while, to top it right up.
Before I started testing I took another reading, it was going from 13.2v to 12.8v as the battery stabilised from it's recent charging.

So, with a generic 300w modified wave inverter, purchased from an ebay seller last season for about £15 (this will be practically identical to ALL 300w modified wave models, from Halfrauds, Argos, Maplins etc etc.

All these readings are testing current drawn, on the 12 volt side. It must be remembered that, as volts go down (ie. battery discharges) amps will go up slightly, as the watts will remain constant (Volts X Amps = Watts).

Just inverter on its own was using around 0.3amps

Inverter powering a 7w energy saving lamp was using 0.77-0.82amps, with a momentary start-up surge of 1.62amps

Now here was a surprise, the laptop charger caused the inverter to draw 2.67-2.72amps, far more than I was expecting. It made no difference weather the laptop was switched on or shut down. But with it disconnected the charger alone used practically nothing, registering around 0.3amps, which is what the inverter uses on its own.

A Sony Ericsson USB type phone charger used nothing when plugged in alone, rising to 0.46amps with the phone on standby, & to 0.52amps with the phone plugged in & in use.

My Phillips beard trimmer charger used 0.37-0.38amps total (this can't be used on the charger)

A 35w desktop cooling fan was tested on all 3 speeds;
Speed 1:- Start-up surge=2.80amps Running=2.76amps
Speed 2:- Start-up surge=3.04amps Running=2.89amps
Speed 3:- Start-up surge=3.30amps Running=3.05amps

Phone, laptop, shaver & lamp altogether were 3.56amps

Phone, laptop, shaver & fan (speed 3 I think?) altogether were 6.39amps

Just the phone charger & low energy lamp together (& good, real world type of usage) used 0.97amps

After this testing, I re-tested the battery voltage. Immediately afterwards it was 12.51v
After a further 10mins (timed) it had settled at 12.73v so still fully charged, although that's not exactly very long to use the inverter (I will do some longer testing next time).

Anyway, I went back when I had found a few more things to plug in. I found......

12v cordless inspection lamp charger, which drew a maximum of 0.58amps, This charger drew 0.37 with nothing connected, so this would be an example of a NON-intelligent charger.

Finally, a 40w soldering iron, drew 3.30-3.20amps (lowering as it got hot).
It was ready to solder in around 3 minutes. Not bad.

All this shows that, with careful use, an inverter & leisure battery will last you for several days, maybe even a week, depending what you run off it.
It's all far less current than I was expecting.

Next, I would like to test an LCD TV with a satellite decoder & possibly a DVD player, for a proper "REAL WORLD" test.
I can't see it using much more, if any more, than the laptop charger though.
So a couple of hours each evening for the kids watching a DVD, or for the adults to watch a movie or bit of telly in the evenings, shouldn't eat your leisure battery up as much as you may have thought.

It's all ongoing though. My dad's lent out his small LCD TV, he'll be getting it back in the next couple of weeks, to use in his caravan, so I'll grab it & test it on he inverter.

[M0KAS]

well i have just put an order in for an inverter, so i can have a play around to, the one i have ordered is on offer from argos, 350w RAC one, current price £16.99, some stores have them in stock and others dont, so i had to pay the £5.95 postage, even so, i dont think it was a bad buy really.. if anybody else wants one, here is the code number and linky to the item http://www.argos.co.uk/static/Product/partNumber/7403954/Trail/searchtext%3EINVERTER.htm i will see what other tests i can perform on the 240v side of things also.

[nutgone]

It might be worth doing some further testing on the 12v side, especially as that's the bit most campers are bothered about.
I only say this as I had a quick go with my dad's inverter yesterday. He's got a 150w one, with just a cigarette lighter plug & it also has no cooling fan, like many of the smaller ones.

Anyway, when the inverter was at rest, ie. nothing plugged in, it used less power than the 300w, only 0.21amps, but when I plugged in the 40w soldering iron (my last test on the other unit) it actually used more power than my 300w inverter, using 4.16-4.28amps, reading higher as it got hotter for some reason, on my inverter it used less as it got hotter, as one would expect.

My dad's unit is slightly older, it used to be mine. It was actually responsible for killing my cordless drill battery charger about 4 years ago, so I wonder if it's one of the older type, that isn't fully isolated between low & high voltage sides, which are no longer produced.
I will have to take it apart & have a look.

I will also borrow my brother's brand new 500w one & see what that's doing. That also has a USB output on it as well.

AFAIK the 230v side works on a 2 phase system, although with no earth I'm not exactly sure how you will test this, but it may mean any current readings will be distorted, as you can only measure current on one pole at a time.
I'm not totally certain about this, as I'm largely going on some testing I did years ago on boats (with generators, inverters & shore lines) & what I've been reading lately on the internet.

My brother's just informed me he'll bring his inverter over today, so I'll top the leisure battery back up & get on with it this afternoon

[nutgone]

I was going to do some more testing today, but got involved with my dad's latest project....

He's fixing a sidecar to his Moto Guzzi.....

[M0KAS]

I was going to do some more testing today, but got involved with my dad's latest project....

He's fixing a sidecar to his Moto Guzzi.....

Dont let Wayne see that piccy, he will be after converting that into a trailer, or even worse a caravan