Ebay 500watt Power Inverter

I recently bought a 500w power inverter from Ebay. I have 100ah LA battery and connected it to the inverter. if the noise of the cooling fan is ignored, it is working fine. I also have few other components connected directly to the battery including a 12v fan, an adsl router etc. but when I run the inverter, I had electric shock on my 12v apps' power pins. Is this normal with this type of inverter or something is wrong?

This thing comes fitted with an internal cooling fan, the noise is so high (under normal room conditions it is unbearable). Though I bought a 500w inverter, it may be used to power led bulbs @220v of 50-80watts(5 to 8 nos x 9watt). with the required power is under 100watts can I remove the cooling fan?

12v cannot give you shock, output of inverter can give you shock though.
Mind you, if you did get a shock off a 12v source, then it may have been a capacitive shock due to the 12v common getting induced up to high voltage by its proximity to the inverter. Usually there is enough leakage in the components that span the isolation barrier to stop this but sometimes not.
Also, maybe it was static shock due to your rubber shoes on the carpet before you touched the 12v.

I had before a ups for computer which had galvanic isolation and don't remember having any such issues.
but the ups .. etc was big , had big transformer and unit was big. I know that technology.
but this inverter that I bought now ( what we have now available) is very small, have very small transformer(!!!), and may be any new technology. the feeling is same as looking at transformer based 12v power supply (old tech - 4 diodes , 1 cap) and then opening and looking at a 12v smps based design and getting surprised by the transformer (SMPS) size.

so what I am saying is that I am new with this type of inverter and is it normal to get a shock at the 12v input pin, or is the system faulty. If it is faulty I have to get it replaced or to do something about the shock myself .

(I am using the battery to supply my 12v fan/emergency light, router, laptop via boost converter etc for the last 1 1/2 years. since I have lot of power here in store (100amp is too much for this purpose ), I decided to extend the use by using as backup power for kitchen and dining room lights. I have to use 30mtr wires for this so I thought to not use the 12v led bulbs and 12v supply but decided to use an inverter and 230v led bulbs, ie the purpose of the inverter).

is the 12v input common earthed?....if it is earthed then I do not understand how you can be shocked from touching it.

I had an experience getting shocked from a 12V automobile system. It was when the battery was low. I asked my mother to start the engine. It would not crank the engine, however it had just enough juice to make the solenoid chatter. I accidentally put my hand on the contact. I was surprised because I felt repeated shocks as the solenoid chattered. This implied that the voltage was going over 100V somehow. I could not understand what was happening to make it do this.

Years later I realized the reason had to do with inductive kick coming from the solenoid turning on and off. Your equipment might do something similar, if has a switching inductor at the input terminals, without filtering or protection.

*** I am not an expert in this but the various explanations I am getting here.. well..
I wrote in one of the above posts - I am using this battery system for 1.5 years , not subjected to electric shock.

just one example. in normal smps based 12v , 15v power supplies the input 230v taken and rectified, filtered, applied as square waves to the transformers via 1 or 2 (or more) transistors/mosfets etc. the secondary output is filtered (lets ignore the other complex electronics on the secondary side) and given as output. There is an opto to connect between pri and secondary (you know what for). There is also a (sometimes) capacitor (decoupling?) that connects the primary and secondary , when damaged will result in an electric shock on the secondary.

My question here is simple and straight forward. in normal inverter the 12v supply is applied to a transformer via transistor/mosfet and 220v supply is available at the output side of the transformer. you may get an electric shock on the output but normally not on the input 12v side. There are options to make power supplies from 230v to 5v etc. without a transformer with capacitor etc. to draw current in milliamps range but you may get electric shock on the output . so with this inverter I bought is there any connection with the input and output so that there is electric shock on the input. is the output leaking to the input?
if this is system fault , I will replace or if it is normal I have no other option.

you would have to remove the Y cap and see if you still get a shock.......perhaps you can test with a meter between earth and the 12v rails. if you do it with finger, as you know, this is not advised, but making sure you have rubber souls on and only touch with one tip of one finger. Don't touch it in two places.
I am wondering of their is problem in the transformer itself, maybe. You would have to buy a flash tester and give it the flash test. -that would be the correct way to do it, ie no touching. flash test is 3500vac for one minute.

treez said:

flash test is 3500vac for one minute.

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Although the standards call for it, the manufacturers never agree for this. High voltage test will kill most, if not all, capacitors and probably the insulation in the transformer will fail. The transformer alone is supposed to pass DC 500V test as a test of good insulation. I am quoting from memory and I could be wrong.

I am very sorry friends , instead of asking a simple question , I really made it look complicated. The listing for item I bought on ebay has ended. it is similar to this : **broken link removed**

when the inverter is off there is no shock on the input pins or on battery terminals. But when I turn on the inverter, there is shock on the input pins. is this normal. any leakage from output to input supply? if it is not normal, I have to contact the seller.
This type of circuit has galvanic isolation ?

Both sides of the box can be opened and then have to remove 2 screws which hold the power transistor to the body of inverter (heatsink). After removing this screw I have to pull out the board to check it, which may be complicated. so after getting your reply I will contact the seller .

The ground on the HV side and the ground on the LV side are distinct but often they are connected with a high voltage capacitor of small capacitance. Some of these box type inverters do not have three pin connection and the ground is not connected. You can test with a neon tester (which can detect leakage of 100uA current) and get a qualitative idea of the current. You can test with a multimeter whether the 12V ground is connected to the metal body (most likely not). If it is not connected, you can use a three pin power connector and connect the body with the socket ground.

Hopefully it will go away. If not, you need to return the item.

as the OP says, the battery is obviously isolated from earth ground, so the output of the inverter should be isolated from earth ground, so it is interesting how the op has managed to get a shock , (which must be to earth ground).
I am suspecting that the 12V rails are getting somehow induced up to a relatively high voltage with respect to earth, and then the op is "discharging" this induced voltage when op touches it.....the thing to do is to connect ONE OF THE 12V rails to earth ground, and then power it up, and then see if you get a shock when you touch it (touch either of the 12v rails NOT TOUCH THE HIGH VOLTAGE OUTPUT!!).

tHIS Could simply be the normal effect of an isolated apparatus getting itself charged up with respect to earth ground.....this is why they have those flap things dangling down from cars.

There should be isolation between input and output of the inverter, but I do not know to which voltage level it is required for it.

treez said:

as the OP says, the battery is obviously isolated from earth ground,

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Obviously this cannot be correct because all potentials are always defined with respect to the earth. The output of the SMPS is obviously coupled inductively and capacitively to the input side. Using a diode rectifier cannot be an isolation because all real diodes have some reverse leakage current.

The isolation between the input and output side of a SMPS is notional at best. The isolation is best at DC and degrades at higher and higher frequencies.

Obviously this cannot be correct because all potentials are always defined with respect to the earth.

Click to expand...

What about a battery on a plane?....you see what I mean....if a battery rail is not connected to earth, then its voltage is not referenced to earth.

Do you think replacing the inverter with another one will fix the issue??

Not necessarily, somehow a voltage has been induced into the rails of the 12v Input.
Putting a ohmmeter across input to output will at least see if there has been a serious breach in the isolation.
Altenatively maybe earthing the 12v side can solve it, -stop it getting induced up in voltage.
I would go onto maplin.co.uk website, pretend you are interested in their inverters and ask if its possible to get a shock like you say, they have a questions page with their products, so you could ask there.

treez said:

What about a battery on a plane?....you see what I mean....if a battery rail is not connected to earth, then its voltage is not referenced to earth.

Click to expand...

For that, we have only potential differences.

Seriously, The current path for the battery and the 12V charging circuit forms a closed loop that is floating. This is inductively coupled to the mains circuit which is grounded at one point. The magnetic coupling and electrical isolation is only notional because on one side we are allowed to lift the ground...

I may have mislead all of you in a way. I am running this inverter and there is shock. To use it well I had it initially connected to the grid (for my room 100wattts load - 65 watts fan and 40watt Tube light) with the breaker to my room turned off. I tried to interchange the wires connected from the inverter to the load, still same. so here the phase connection to my room is disconnected but the neutral is still intact. That is where the shock coming from.
(I completely isolated the inverter from the current setup and connected a laptop and 60watt load to the inverter output and I am not getting electric shock.)

May be I am doing something wrong here. But I am connecting it to grid or not, is it normal to have electric shock on the input( considering the transformer isolation)?

AFAIK these so called "High-Frequency double conversion type Inverters " have no isolation between output H-Bridge (DC-AC) stage & Input push-pull (DC-DC) stage ... the grounds are tied together .. so always expect a shock when you connect these types of inverters to mains grid ...

The distance between the battery and the proposed 12v led bulb were 30+ mtrs and someone told me it is not a good idea to send 12v over the wire for that long distance and I thought of using an inverter and use this as a backup supply for the existing 5nos 230v LEDS. with this electric shock hazard I will use few completely isolated LED bulb as backup setup , to avoid any issues.
With the proposed load being around 50watts, with this inverter capable of supplying 500watts, I think removing the cooling fan to avoid the noise will not be an issue.