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Battery powered 230VAC Inverter, safety precautions?

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Re: Battery powered 230VAC Inverter, safety precautions?

Postby Sam Spoons » Mon Dec 09, 2019 1:27 pm

Deep cycle batteries are designed to cope with being discharged to lower voltages than cranking type batteries, I don't think it makes much difference to the effective capacity but they last many more charge/discharge cycles used correctly. Car starter batteries can supply much higher amperages, typically several hundred amps, which would damage a deep cycle battery.
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Re: Battery powered 230VAC Inverter, safety precautions?

Postby Sam Spoons » Mon Dec 09, 2019 1:35 pm

Folderol wrote:
Sam Spoons wrote:My 18 watt combo draws around 0.34A from the mains at normal/gig volume so you should be well within the capability of that inverter. I might stick the 'scope on the output from my new power pack later and see what the 'modified sine wave' looks like.

I can tell you now. It will look horrible and nothing like a sine wave! Especially if only lightly loaded.

A true sinewave will actually be more efficient (as well as electrically quieter) as the transformer is not getting slammed with hard step sequences.

How do SMPSUs react to being supplied power as a 'modified sine wave'?
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Re: Battery powered 230VAC Inverter, safety precautions?

Postby Folderol » Mon Dec 09, 2019 2:50 pm

Modern ones don't care. The first thing they do is rectify and smooth it. The cap will have a slightly lower peak ripple current, so in theory will last longer, but whether that is measurable is moot. It's the EMI suppression that will have most trouble - all those lovely harmonics :tongue:
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Re: Battery powered 230VAC Inverter, safety precautions?

Postby Sam Spoons » Mon Dec 09, 2019 2:55 pm

Thanks Will. :thumbup:
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Re: Battery powered 230VAC Inverter, safety precautions?

Postby ef37a » Mon Dec 09, 2019 3:40 pm

Can we not build a 50Hz resonant filter like the tank circuit for a class C transmitter?

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Re: Battery powered 230VAC Inverter, safety precautions?

Postby Hugh Robjohns » Mon Dec 09, 2019 4:02 pm

Sam Spoons wrote:I might stick the 'scope on the output from my new power pack later and see what the 'modified sine wave' looks like.

Image

This website will give you some more info (although the way that 'scope is set up doesn't make it very clear what's going on!)

https://www.altestore.com/blog/2015/10/pure-sine-wave-vs-modified-sine-wave-whats-the-difference/#.Xe5hq5P7TRY
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Re: Battery powered 230VAC Inverter, safety precautions?

Postby Folderol » Mon Dec 09, 2019 5:26 pm

Exactly!
I really don't know how they can get away with calling it 'modified sine'. It bears no resemblance at all to a sine wave, and is a positively evil thing to do to an innocent transformer - I rather suspect that the one in the inverter has a bit of an air gap to reduce the chance of core saturation, although that will reduce the efficiency even further :protest:

P.S.
Actually the drawing is wrong. That is the voltage waveform, the current one would be exponential curves.
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Re: Battery powered 230VAC Inverter, safety precautions?

Postby ef37a » Mon Dec 09, 2019 5:34 pm

Folderol wrote:Exactly!
I really don't know how they can get away with calling it 'modified sine'. It bears no resemblance at all to a sine wave, and is a positively evil thing to do to an innocent transformer - I rather suspect that the one in the inverter has a bit of an air gap to reduce the chance of core saturation, although that will reduce the efficiency even further :protest:

B.b.b.b.but! In another thread we were talking about car radios of old and vibrators (shut up that boy at the back!) They must have produced a very similar waveform? Never had a traff go.

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Re: Battery powered 230VAC Inverter, safety precautions?

Postby Folderol » Mon Dec 09, 2019 5:48 pm

ef37a wrote:
Folderol wrote:Exactly!
I really don't know how they can get away with calling it 'modified sine'. It bears no resemblance at all to a sine wave, and is a positively evil thing to do to an innocent transformer - I rather suspect that the one in the inverter has a bit of an air gap to reduce the chance of core saturation, although that will reduce the efficiency even further :protest:

B.b.b.b.but! In another thread we were talking about car radios of old and vibrators (shut up that boy at the back!) They must have produced a very similar waveform? Never had a traff go.

Dave.
They were square wave, and definitely were air gapped. I know, cos I took one apart in my yoof. They were also distinctly low efficiency. The radio I had drew 5-6A from a 12V battery :o
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Re: Battery powered 230VAC Inverter, safety precautions?

Postby Sam Spoons » Mon Dec 09, 2019 5:50 pm

Of course I wouldn't be having this trouble if Berry had built the XR12 with a 12V line rat PSU like my Mackie DL1608 instead of a built in jobbie :headbang:
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Re: Battery powered 230VAC Inverter, safety precautions?

Postby Folderol » Mon Dec 09, 2019 5:58 pm

Hmmm. What's the rated power consumption, and how old is it?
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Re: Battery powered 230VAC Inverter, safety precautions?

Postby Sam Spoons » Mon Dec 09, 2019 6:23 pm

Didja mean the DL or Dave car radio?

The DL is rated 12VDC and 48 watts so by my reckoning a 7AH SLA battery would only run it for an hour or so, possibly less, before the voltage dropped too far. Maybe my Anker Li-Ion battery pack would fare better as it has a regulated 12VDC output. I'd give it a try but the power connector in the DL is unconventional and I don't have a spare handy.....
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Re: Battery powered 230VAC Inverter, safety precautions?

Postby Folderol » Mon Dec 09, 2019 7:10 pm

Nooo. I meant the Berry :roll:
The thing is you're currently doing two conversions, neither of them particularly well.
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Re: Battery powered 230VAC Inverter, safety precautions?

Postby wireman » Mon Dec 09, 2019 9:26 pm

Hugh Robjohns wrote:
Sam Spoons wrote:I might stick the 'scope on the output from my new power pack later and see what the 'modified sine wave' looks like.

Image

This website will give you some more info (although the way that 'scope is set up doesn't make it very clear what's going on!)

https://www.altestore.com/blog/2015/10/pure-sine-wave-vs-modified-sine-wave-whats-the-difference/#.Xe5hq5P7TRY

I should look at the output of my UPS to see what the waveform looks like, not sure if I can post the result however and it will be a couple of weeks before I can try.
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Re: Battery powered 230VAC Inverter, safety precautions?

Postby blinddrew » Mon Dec 09, 2019 9:27 pm

Folderol wrote:The thing is you're currently doing two conversions, neither of them particularly well.
That eloquently sums up my day.
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