Inverter reverse current
Submitted: Thursday, Mar 27, 2008 at 12:06
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Member - Troll 81 (QLD)
Inverter reverse current
My 7 year old 300w inverter has finally decided to start playing up. I have had many good camping trips with it. Over the weekend I was running a 48w fluro light and I went to the car to grab a beer out of the Engel and when I touched the hatch to open the lid I got a little zap and felt some current running through me. This obviously gave me a fright and I thought the fridge was faulty. So I unplugged the Engel and tried again and the current was still there. I then went around to the engine bay to
check voltage and stuff at the battery and again when I went to open the bonnet I got a nasty zap. I then relised that it must be the inverter causing this. I turned it off straight away after this and used my other inverter and the problem went away.
Does anyone have any theories as to why this happened? I am guessing it’s just age and I good really good service out of it?
Reply By: Member - John and Val W (ACT) - Thursday, Mar 27, 2008 at 14:55
Thursday, Mar 27, 2008 at 14:55
Troll -
Suggest first, satisfy yourself it's not just a static electric bite - the sort of zap we all get occassionaly by sliding out of a vehicle then touching the vehicle.
If you're convinced it's coming from the inverter, talk to an electrician (not an autoelectrician, a mains type person.)
To get a shock from mains voltages such as your inverter produces, electric current must flow through you. One side of the 240V mains supply is connected to ground, so many electric shocks result from standing on the ground and somehow coming in contact with the other side of the mains supply.
With an inverter though, there isn't any obvious connection to the ground, so standing on the ground and touching the vehicle shouldn't result in any current flowing through you, so no shock. Get someone with a suitable meter and knowhow to make a few measurements.
When dealing with mains voltages, if in any doubt, touch with the back of your hand fiirst, not the front - that way if it is dangerous you'll jump away, not have your hand forced closed to grip it tighter. Better still - let someone else do it!
HTH
John | J and V
"Not everything that can be counted counts, and not everything that counts can be counted."
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Follow Up By: Member - Troll 81 (QLD) - Thursday, Mar 27, 2008 at 15:00
Thursday, Mar 27, 2008 at 15:00
John
When I went to open the bonnet I had to use the bonnet clip thing to unlatch and even then I felt it going through me. After I turned the old inverter off I went and touch everywhere I got zapped before and there was nothing.
I am 100% sure it was coming from there. I am not even going to try and turn it back on I am just more curios as to why. I am so proud of this little inverter it might get a little spot in my wall behind the bar for lasting so long :)
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Reply By: gasgas - Thursday, Mar 27, 2008 at 20:45
Thursday, Mar 27, 2008 at 20:45
It sounds like there is a short between the 240v Active and the 12v Negative inside the inverter, thus causing the vehicle to become live and anything else that is connected to the battery (your fridge)
WITHOUT POWERING UP THE UNIT you can prove this by using an ohm meter to measure the resistance between the Active pin on the inverter (left hand side as u look at the 3 pin outlet) and the negative terminal.
Shoul read a low resistance if my hunch is right.
PLEASE, DO NOT PUT POWER ON THE UNIT UNTIL YOU HAVE HAD IT CHECKED BY SOMEONE QUALIFIED
AnswerID:
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Follow Up By: Member - Troll 81 (QLD) - Thursday, Mar 27, 2008 at 20:56
Thursday, Mar 27, 2008 at 20:56
Thanks for your reply sounds like you are onto something,
The plan is to leave it unplugged for good. The unit has served me for 7 years and I am happy with that.
FollowupID:
561041
Reply By: avro - Thursday, Mar 27, 2008 at 21:47
Thursday, Mar 27, 2008 at 21:47
You almost certainly have an inverter that does NOT have the secondary winding (the 240 volt one) isolated from the primary (the 12 volt one). Unfortunately most of the older
inverters were like this, and unless it clearly states that it is isolated (all the recent Jaycar ones are) it almost certainly is not. In effect these have a single winding, tapped at one end for 12 volts. These are potentially dangerous and in my view should not be sold or used. They have recently been banned on Victorian worksites I understand, but should be banned everywhere.
You usually need to touch both an active and an inactive to get a big (usually lethal) belt, but the capacitance of your body canl cause a small current to flow and give you a tingle (or worse). My advice is to cut the leads off (so it cannot be used again) and throw it in the rubbish bin.
Regards avro
AnswerID:
295117
Follow Up By: unimog - Thursday, Mar 27, 2008 at 22:23
Thursday, Mar 27, 2008 at 22:23
Avro is on the ball, absolutely correct.
Oh, by the way, if you really like the feeling of being electrocuted you might be able to still buy the 'old' type of
inverters, brand new from China for not much more then a few dollars...
Banned, but still available... where? on Ebay, where else..
FollowupID:
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Reply By: Nomadic Navara - Thursday, Mar 27, 2008 at 21:48
Thursday, Mar 27, 2008 at 21:48
Being 7 years old it is possible that the primary winding in its transformer is also part of the secondary winding (called an auto transformer.) If one of the output leads had leakage to ground then the whole of the car could have been live.
Most of the newer
inverters have the primary and secondary windings of their internal transformer isolated from each other. Always purchase
inverters that have their 240V output electrically isolated from the 12V circuit. You can
check if there is isolation with the ohms range on your multi meter. Disconnect the inverter from everything. If there is an input switch on it switch this on. Set the multi meter to a low ohms range and
test to see if there is any resistance between either of the input leads and the output leads. If there is any resistance between an input lead and either of the output leads it is not an electrically isolated unit and should be thrown out or used with caution.
To see what an auto transformer is
go to this link
PeterD
AnswerID:
295118