Weird 330w inverter question

Submitted: Friday, Jan 21, 2005 at 10:55
ThreadID: 19647 Views:2703 Replies:11 FollowUps:10
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Hi all

I have recently wired 40 amp-capable cable directly from a heavy fuse box near my battery to the rear of the car and fitted an Arrid power socket there for my fridge, lights, etc. I tried my 330w inverter on it yesterday and "boom!" - I took out the 20 amp fuse in my fuse box as I turned it on. I know the inverter works as I have just removed it from my other car.

Given that it's a 330w jobbie, I presume that at full continuous capacity it will be drawing around 27 amps. But in this case there was no load!!!! I just plugged it in - that's all. I replaced the fuse with a 30 amp one and it did it again. I wasn't prepared to go any higher as I'd be approaching the limit of the wiring's maximum rating.....

Does anyone here know what the idle current on these things is meant to be - in approximate terms? Or, have I suddenly (literally overnight) got a bad inverter?

It used to run a 25-amp fuse in the old car and there were never any problems.

Cheers and thanks for any advice :)

Chris
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Reply By: Member - Chrispy (NSW) - Friday, Jan 21, 2005 at 11:02

Friday, Jan 21, 2005 at 11:02
PS - All my other devices (fridge, lights, etc work on this circuit - so it, in itself, is fine......
AnswerID: 94238

Reply By: Penguin (NSW) - Friday, Jan 21, 2005 at 11:12

Friday, Jan 21, 2005 at 11:12
Hi Chris,

I had a similar problem with my inverter connected through a fuse in my camper - just kept blowing. I'm not sure about the pure sine wave models but my "modified" (read square wave) one seems to drag a huge amount of current on startup.

If you have access to an ammeter, check out what the startup current is and go from there. If not, we're both in Sydney - send me a MM.
AnswerID: 94242

Reply By: Member - Alan S (NSW) - Friday, Jan 21, 2005 at 11:13

Friday, Jan 21, 2005 at 11:13
Hi Chris,
I have a 400w invertor and on the specifications its supposed to draw 0.9amp with no load.
Can you try the invertor on a different 12 volt source, from what you have described its sounds like its stuffed to me
AnswerID: 94243

Reply By: Baz (NSW) - Friday, Jan 21, 2005 at 11:23

Friday, Jan 21, 2005 at 11:23
Hey Chris inverters are a funny thing we have 2 a 300w pure sine wave and a dick smith 300w modified, the Pure sine when connected to the car to run our charger that charges our battery in the camper just sits there clicking on off on off it is strange and the charger does the same but the DS cheapy runs our charger no probs.

I have heard that they can just stop working suddenly as they are not very durable and shaking about in a vehicle is not good for them.

Baz.
AnswerID: 94244

Follow Up By: Utemad - Friday, Jan 21, 2005 at 11:38

Friday, Jan 21, 2005 at 11:38
Inverters can be a bit strange. My 200w (til it blew) would power my laptop but not my Dad's. However his 300w wouldn't power mine or his but it powered everything else fine. Strange.
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FollowupID: 353243

Follow Up By: firestang - Friday, Jan 21, 2005 at 16:33

Friday, Jan 21, 2005 at 16:33
If i run my inverter in the work van for something that doesn't draw much current it will click on off on off all the time as you said yours does . If i plug something else in at the sme time it runs fine , it needs a bit more current draw ,mine does anyway .
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FollowupID: 353291

Reply By: Utemad - Friday, Jan 21, 2005 at 11:35

Friday, Jan 21, 2005 at 11:35
Mine did the same thing as yours about two weeks ago. It was powering the laptop no probs and then I noticed the laptop wasn't charging so I checked everything over and found the fuse had blown for the inverter. I replaced it and it blew too. I later dicovered that a screw had rattled itself loose inside and shorted something out. It was the screw for the earth terminal of the 240v output connector. Now I'm up for a new inverter :-(
AnswerID: 94245

Reply By: Member - Chrispy (NSW) - Friday, Jan 21, 2005 at 11:46

Friday, Jan 21, 2005 at 11:46
Thanks guys :)

Yup - I just found a neighbour who had a multimeter that actually worked :(

I connected it up with the main switch "off" and there was a slight spark from the terminals as I connected.

Once connected it was drawing 0.00A

I turned it on (with no load) and it drew 0.25A

I connected a light with a 60-watt globe and it drew 3.94A

So... stuff-all really.

Must be the initial contact with the power-source (slight spark) that does it. What a pain!!! I wonder if I can electrically damp that with something..... ??

Oh well. I'll just have to connect directly to the battery for this weeken using some alligator clips.

Cheers and thanks for the help!!
Chris
AnswerID: 94247

Follow Up By: MrBitchi - Friday, Jan 21, 2005 at 14:03

Friday, Jan 21, 2005 at 14:03
A digital multimeter when used as an ameter will never catch the startup current. The display response is too slow. Try replacing the fude with a solid state circuit breaker. Might handle the startup surge a bit better.
Your local Narva stockist should be able to help you out.

Narva No. 54630

Cheers, John.
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FollowupID: 353272

Reply By: hl - Friday, Jan 21, 2005 at 12:06

Friday, Jan 21, 2005 at 12:06
Hi,

Many inverters have a rather large capacitor across the input. It can create quite a surge when you first connect it, makes no difference whether the inverter is on or off. (will also spark quite a bit if you disconnect and short the alligator clips)
A slow blow fuse should take care of it, or better still use a circuit breaker. I have a 70 amp breaker directly at the aux battery before the cables that go through the firewall. I still use individual fuse blocks for the lighter load circuits, but the 70 amp breaker should blow when all else fails or if a cable gets pinched somewhere, perhaps in a crash.
I am surprised though that it blew a 30 amp fuse.
The idle current on modified square wave units is usually much less than 1 amp, the sine wave units are less efficient and have higher idle currents.
Cheers

AnswerID: 94251

Follow Up By: Member - Chrispy (NSW) - Friday, Jan 21, 2005 at 12:14

Friday, Jan 21, 2005 at 12:14
hl - thanks for that.

Any idea what size capacitor might do the trick? I presume I could simply run it between the two screw terminals if it won't fit inside the case....... correct?
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FollowupID: 353254

Follow Up By: Member - Chrispy (NSW) - Friday, Jan 21, 2005 at 12:16

Friday, Jan 21, 2005 at 12:16
PS - Do you know if slow-blow fuses come in blade format? I know the barrel types do......
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FollowupID: 353256

Follow Up By: hl - Friday, Jan 21, 2005 at 13:48

Friday, Jan 21, 2005 at 13:48
Hi Crispy,

You misunderstood me. That capacitor (or a bank of them) is already there inside the inverter and it causes the surge.
To prove my point and overcome the problem temporarily, just connect your inverter directly to the battery, to charge the capacitor. Don't turn it on though, then connect it to where u wanted it. It should not blow the fuse this time if my theory is correct. I don't think the blade fuses come in slow blow.
Cheers
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FollowupID: 353267

Follow Up By: Member - Chrispy (NSW) - Friday, Jan 21, 2005 at 13:54

Friday, Jan 21, 2005 at 13:54
hl

Ahhhh!! I see.

I was under the assumption that it may not have a smoothing capacitor in this one..... I would hope so, but you'd never know with the cheapies.

I'll try your theory out.

Cheers and thanks again
Chris
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FollowupID: 353268

Reply By: ianmc - Friday, Jan 21, 2005 at 13:19

Friday, Jan 21, 2005 at 13:19
I have used a 330w Digitor inverter for some time thru the cig lighter plug .It has that type of plug supplied with it & its been no trouble at all.
330w is about 1.5amp at 240v plus what theinverter _Affordable_Storage_Drawers.aspx so fusing shouldnt be a problem.
AnswerID: 94259

Follow Up By: hl - Friday, Jan 21, 2005 at 13:54

Friday, Jan 21, 2005 at 13:54
Hi...

It is that at 240V... but your inverter will pull more than 25 amps at full load to produce the 240V output. Far too much for the cigarette lighter circuit (and the plug for that matter).
Just running a laptop won't be a problem though.

cheers
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FollowupID: 353269

Follow Up By: Member - Chrispy (NSW) - Friday, Jan 21, 2005 at 13:56

Friday, Jan 21, 2005 at 13:56
Yup 330 / 12 = 27.5A
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FollowupID: 353270

Reply By: Redeye - Friday, Jan 21, 2005 at 14:44

Friday, Jan 21, 2005 at 14:44
Hi,

330/12 is correct if the inverter was 100% efficient. The actual current draw will be in excess of 27 amps by the % of inefficiency. Possibly 10% to 20%

Also have you tested the socket to ensure that the +ve is the tip. A reversed power feed may also cause a product to draw excessive current and blow fuses.

Using a cigarette lighter socket to power anything that _Affordable_Storage_Drawers.aspx current for extended period is asking for problems. The wiring is designed for short bursts of power to heat the lighter not continuos current draw.

Garry
AnswerID: 94280

Follow Up By: Member - Chrispy (NSW) - Friday, Jan 21, 2005 at 14:52

Friday, Jan 21, 2005 at 14:52
You are quite right in regard to efficiencies... but I was just making a general statement :)

I have very solid 8mm cable from the battery right through to the socket. I don't use ciggy lighter sockets as they are useless in terms of vibration resistance and general quality of connection. I use a German made variation of the Arrid sockets that are built to take 40 amps or thereabouts. I can't see the brand name on it though....

The polarity is correct.

Cheers
Chris
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FollowupID: 353277

Reply By: Member - Craig M (NSW) - Friday, Jan 21, 2005 at 22:26

Friday, Jan 21, 2005 at 22:26
Hi Guys,
Just a bit of info I found in the latest DSE catolouge concerning inverters.
It says that using the standard form of inverter (modified sine) is not recomended for continuous running of a laptop due to the fact that it will stuff up the laptops battery. They recomend using the pure sinewave inverter if using continuous to power a laptop.

Cheers
AnswerID: 94352

Follow Up By: hl - Saturday, Jan 22, 2005 at 08:42

Saturday, Jan 22, 2005 at 08:42
Hi,

Yes, I saw that too... Wonder who made that assumption. I can't see any reason at all why it would do that!

Cheers

(Laptop batteries do a wonderful job of stuffing themselves under any conditions)

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FollowupID: 353350

Reply By: Member -Dodger - Saturday, Jan 22, 2005 at 15:57

Saturday, Jan 22, 2005 at 15:57
Most small inverters like you have should not exceed about an amp on start. If you are switching it on unloaded and blowing fuses than there is either a defect with the inverter or the way its connected. Even on full load it should not exceed 29 amps. To test for internal problem disconnect the inverter and use a multimeter on resistance and check what resistance reading you get between the pos and neg on the inverter. Also check the supply socket in case the connections are shorting.

cheers

Dodger
I used to have a handle on life, but it broke.

Cheers Dodg.

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AnswerID: 94412

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