Actual voltage of an Invertor

[Deleted User] · 31-03-2010 2:49am #1

This is a subject I've spent the last 4 hours googling with not one satisfying answer.

Has anyone metered their invertor and if so what did they get?

I just bought a 600watt and it says "12v -> 230AC"
in the manual it says +/- 5% giving me 220v to 240v variable like real electricity.

What I found was that the output at 12.4Vdc is 204.3Vac, which further drops to 195Vac under load.
Giving the product the benefit of the doubt I charged my leisure battery to 14.3Vdc which gave me 187.5Vac and 178.5V under load.
This is a colossal 22% drop in voltage on a fully charged battery.
All well and good for light-bulbs, motor based appliances and things like phone chargers with built in transformers but surely electronics are going to have problems with this.
Any thoughts?

Buford T Justice · 01-04-2010 1:29pm

It will also depend on the AH of the battery too. How much of a load are you pulling off the inverter?

*Kol* · 01-04-2010 3:13pm

Sir Liamalot wrote: »

This is a subject I've spent the last 4 hours googling with not one satisfying answer.

Has anyone metered their invertor and if so what did they get?

I just bought a 600watt and it says "12v -> 230AC"
in the manual it says +/- 5% giving me 220v to 240v variable like real electricity.

What I found was that the output at 12.4Vdc is 204.3Vac, which further drops to 195Vac under load.
Giving the product the benefit of the doubt I charged my leisure battery to 14.3Vdc which gave me 187.5Vac and 178.5V under load.
This is a colossal 22% drop in voltage on a fully charged battery.
All well and good for light-bulbs, motor based appliances and things like phone chargers with built in transformers but surely electronics are going to have problems with this.
Any thoughts?

What are you planning to power from this invertor? Did you have the inverter connected directly to the battery with crocodile clips? I must meter mine later to se what it produces.

paddyp · 01-04-2010 3:21pm

Did you measure 14.3v under load I imagine no way. Under load you will find that the battery voltage drops and the output drops proporionally. Is this a piece of chinese junk you bought off ebay and how much load are you putting on it. If you want to run 600w off it I'd be looking at getting at least a 2kw inverter.

What size cabling are you using on the 12V side?
What length are the cables?

For 600w you're drawing 50A plus the loss in the inverter and will need a beefy cable especially over long distances.

Aidan_M_M · 02-04-2010 12:40am

paddyp wrote: »

Did you measure 14.3v under load I imagine no way. Under load you will find that the battery voltage drops and the output drops proporionally. Is this a piece of chinese junk you bought off ebay and how much load are you putting on it. If you want to run 600w off it I'd be looking at getting at least a 2kw inverter.

What size cabling are you using on the 12V side?
What length are the cables?

For 600w you're drawing 50A plus the loss in the inverter and will need a beefy cable especially over long distances.

He's outputting 600w at (theoretically!) 220 volts , so it's actually only less than 3 amps.

A 600 w , 220v invertor draws around 15 amps from the 12v side .IIRC .

*Kol* · 02-04-2010 1:01am

I checked a cheap 150 watt inverter earlier and it was putting out about 190 volts. I have never had much use for it tbh anyway but it seems to work fine with small items like phone chargers, nintendo chargers and the like. But for most things like that you can get cigarette lighter plug type chargers that run off 12v which is much handier. Most flat panel TV's will run off 12v and you can get laptop chargers that run off 12v too. I don't have anything else that I need 220v for in the MH.

[Deleted User] · 02-04-2010 5:59am

I loaded it with a 60watt bulb for my diagnostics. 5amps I think. (I'm not sure if the denominator is 240 or 12 given the circuit, I'd imagine 0.3amps too low for a mains light - so to me at 600watts 50amp sounds right, and corroborates the battery manufacturer's spec.) www.satellitetv.ie/shop/download/battery.pdf

Yes it was the cheapest I could find from Maplin, which states quite boldly "12v -> 230AC" with +/- 5%...in much smaller print in the manual.
My battery is a new electrosol 125A. The leads from the inverter are 0.5m long and 15mm thick including insulation.

I've since checked a colleague's invertor from his car which read 184v off what I imagine is an 80a starter battery connected to an idling engine alternator.

I overspec-ed the invertor, I intend to pull 150watts from it. My other demands I'm using specific up amps or direct 12v.

14.4v was a momentary peak reading after I charged the leisure battery. 12.04v = 188vAC and 187v under load if I'm going to split hairs on my consumer rights.
(I've noticed the load doesn't proportionally effect the voltage, it's the same drop for 60w as for 360w)

The intended use is a 50watt surround sound system, possibly a 50watt-ish LCD, and what may else come on an "I'm up the side of a mountain and I can't find a socket" situation.
LCD's are allegedly finicky about voltage which I've been humming and ha-ing about.

The query is really;
What damage is caused by under-powering electronics?
and has anyone got and invertor that does what it says on the tin?

PS.

Aidan_M_M wrote: »

He's outputting 600w at (theoretically!) 220 volts , so it's actually only less than 3 amps.

A 600 w , 220v invertor draws around 15 amps from the 12v side .IIRC .

Can you show me how you calculated this? What is IIRC?

martyc5674 · 02-04-2010 11:02am

P=V*I
600w = 220v * 2.73A

Assuming a 100% efficiency that would translate to the 12v side aswell.

P=V*I
600W = 12V * 50A

But its more likely to be about 80% or 90% efficient so probably around 60amps on the 12V for 600W on the 220 side.

Marty.

paddyp · 03-04-2010 1:21pm

Aidan_M_M wrote: »

A 600 w , 220v invertor draws around 15 amps from the 12v side .IIRC .

You'd be a wealthy man if you could make that one work.

Volts x Amps = Watts
12 x 15 = 180W

marty wrote:

probably around 60amps on the 12V for 600W on the 220 side.

Spot on

Sir Liamalot wrote:

The query is really;
What damage is caused by under-powering electronics?
and has anyone got and invertor that does what it says on the tin?

Most modern electronics use a switching power supply if the electronics are rated for dual voltage 100 - 220V they will more than lightly have been tested between 80 and 270V. If the supply is dual voltage rated and as long as you have a relatively clean ac supply it will probaby be fine.

You say the voltage remains approximately the same with differing load which mean the feedback for regulation is working but the feedback is the wrong value. There may be an adjustment in it as its so cheap.

Assuming you have a good connection to the battery and the right sized cables the inverter is out of spec and you are perfectly entitled to land it back on their counter for a refund.

Have a look here for some cheap chinese junk that works.

http://www.dealextreme.com/details.dx/sku.21983

[Deleted User] · 05-04-2010 8:49pm

I'd imagine what you're referring to is for example a computer with a 110v / 220v switch. Or instruments that use low voltage to begin with that necessitate a transformer for instance phone chargers and laptops.

There are however a lot of appliances such as the 5.1 surround system in question with a standard 13amp plug unrestricted. Which reads 220v - 230v. I'm guessing a lower voltage would reduce the frequencies to something out of range of the amp.

Similarly circuitry will run at a higher current to compensate for the reduced voltage, generating heat the product was not designed for;
where I =P/V.
Not to mention that if said devices have fans directed from the mains inlet the fans are revolving slower.

That said I've only a layman's grasp of electronics, which is why I'm asking. For instance most ciruitry would run on signal level voltage so would it be safe to assume that electronics expecting mains will rectify what they get anyway? Stated or otherwise on the back of the appliance? I'd imagine there is a certain tolerance vs lifespan arrangement.

In any case 180v is taking the piss. So I'm going to try for another invertor, this time I'm bringing a multimeter with me. The only problem with slapping it on the counter is that I bought it online because the price in the UK from Maplin was about €20 less including postage. They don't reply to customer service emails, and they screen their product reviews.

Does this cheap Chinese junk give 230v? It looks like a bargain.

Richie15 · 05-04-2010 9:18pm

Sir Liamalot wrote: »

What is IIRC?

I believe it stands for "if I remember correctly".

[Deleted User] · 05-04-2010 10:02pm

oh right i thought it was something fancy about induced residual current or somesuch...thanks for clearing that one up

paddyp · 06-04-2010 1:34am

Sir Liamalot wrote: »

There are however a lot of appliances such as the 5.1 surround system in question with a standard 13amp plug unrestricted. Which reads 220v - 230v. I'm guessing a lower voltage would reduce the frequencies to something out of range of the amp.

Does this cheap Chinese junk give 230v? It looks like a bargain.

Transformers are large, heavy, contain a lot of copper and require large capacitors to smooth the output. Switch mode power supplies can produce the same output for vastly ranging input voltages, utilise a tiny fraction of the weight and copper the main cost is a small inductor/transformer and a transistor with very low on resistance. Thats why most electronics now use switchmode power suplies. It is unusual these days to see single voltage supplies as a result.

http://en.wikipedia.org/wiki/Switched-mode_power_supply

Regarding the dealextreme inverter i haven't used it myself but it receives good reviews including a person who claims to be like myself an electronic engineer who has dismantled it. I find their reviews to be accurate unlike maplins.

Frequency in this case has nothing to do with it i can give you 50hz at femtovolts or 50hz at megavolts.

Lightly you have bought a discrete inverter design from the 70s there are integrated circuits available now that encapsulate all the funtions of the switched mode supply into a tiny package and require about 4 external components. These are then ripped off and churned out in china for a tiny fraction of the cost. A sub 20$ chinese supply could easily outperform the maplin inverter in every area.

[Deleted User] · 06-04-2010 3:41am

thanks paddyp, i hear you knocking.

[Deleted User] · 06-04-2010 5:27pm

I've gotten a reply from Maplin customer services.

"
Dear Mr ...

Thank you for your email.

This sounds normal if testing it with a common multimeter. Using a true RMS multimeter will give the true RMS mains voltage.

What you are measuring here would be an average of the AC power.

Kind Regards
...
"

Indeed I've tested my clamp meter and noticed some major inconsistencies in the readings. Given that I had all the known parts of the equation I couldn't get the ampage to line up either.

I humbly apologise for crying wolf.
This reminds me of the time we forgot to PAT test the PAT tester.

"Unlike averaging meters, which can accurately measure only pure
sinewaves, True RMS meters accurately measure distorted
waveforms." - fluke user manual

Actual voltage of an Invertor

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