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Battery powered 230VAC Inverter, safety precautions?

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Re: Battery powered 230VAC Inverter, safety precautions?

Postby Sam Spoons » Thu Dec 12, 2019 6:41 pm

Next job, maybe, replace the cheap inverter in the VJ for a pure sine wave jobbie, I'll be able to afford one if Foldy's serious abut buying the beers ;)
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Re: Battery powered 230VAC Inverter, safety precautions?

Postby Hugh Robjohns » Thu Dec 12, 2019 6:43 pm

Good result. Makes sense, though. 'Modified sine wave' inverters and UPS boxes are the works of Beelzebub. ;-)

H
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Re: Battery powered 230VAC Inverter, safety precautions?

Postby Sam Spoons » Fri Dec 13, 2019 1:35 am

Never thought of my UPS boxes, I suspect they, being cheap, are MSW not PSW inverters. I suppose they only need to work for a few minutes if the power goes down to let me shut down the digital desk and the main rig will also be off so I won't hear if they are introducing any noise.........

In practice is the modified sine wave inverter in my battery powered VJ going to damage the power tranny or smoothing caps (or any other bits for that matter)?
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Re: Battery powered 230VAC Inverter, safety precautions?

Postby Folderol » Fri Dec 13, 2019 11:14 am

Sam Spoons wrote:Never thought of my UPS boxes, I suspect they, being cheap, are MSW not PSW inverters. I suppose they only need to work for a few minutes if the power goes down to let me shut down the digital desk and the main rig will also be off so I won't hear if they are introducing any noise.........

In practice is the modified sine wave inverter in my battery powered VJ going to damage the power tranny or smoothing caps (or any other bits for that matter)?

Depending on the quality of the transformer, yes it could damage it. The rest, probably not.
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Re: Battery powered 230VAC Inverter, safety precautions?

Postby Sam Spoons » Fri Dec 13, 2019 12:47 pm

Although it's the standard Epiphone tranny so probably not great quality but I believe they are well overrated. There is a new circuit board* that replaces the original and runs two EL84s for 18 watts, you obviously have to change the OP tranny 'cos it's push pull not single ended but the power tranny is supposed to be up to the job.

If I ever get around to doing the conversion I'll definitely install a pure sine wave inverter

* https://www.gapcb.com/products/baby-will-pcb
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Re: Battery powered 230VAC Inverter, safety precautions?

Postby ef37a » Fri Dec 13, 2019 12:55 pm

Folderol wrote:
Sam Spoons wrote:Never thought of my UPS boxes, I suspect they, being cheap, are MSW not PSW inverters. I suppose they only need to work for a few minutes if the power goes down to let me shut down the digital desk and the main rig will also be off so I won't hear if they are introducing any noise.........

In practice is the modified sine wave inverter in my battery powered VJ going to damage the power tranny or smoothing caps (or any other bits for that matter)?

Depending on the quality of the transformer, yes it could damage it. The rest, probably not.

Not so sure Will. Transformers have to cope with rectifiers that just take gulps of current over a very small part of each cycle.

Maybe there are some caravan/boating enthusiasts here that have MS inverters and they can tell of their experiences?

I can say that in 40 odd years in retail electronics servicing and a few gitamps and hi fi amps, I saw very, very few faulty power transformers. Valve OP traffs were a more common problem but even here, rare and due mainly to TV components being cut to the bone.

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Re: Battery powered 230VAC Inverter, safety precautions?

Postby Sam Spoons » Fri Dec 13, 2019 1:27 pm

Might still change it just to get rid of the buzz. Found this on Amazon but it looks too good to be true at that price, what do you think?

https://www.amazon.co.uk/Almencla-Power-Inverter-AC220V-Ports/dp/B07V63S3BC/ref=sr_1_13?keywords=pure+sine+wave+inverter&qid=1576239800&s=electronics&sr=1-13
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Re: Battery powered 230VAC Inverter, safety precautions?

Postby Guest » Fri Dec 13, 2019 5:02 pm

unless it came out of a shop, I would just stick with branded names
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Re: Battery powered 230VAC Inverter, safety precautions?

Postby Folderol » Fri Dec 13, 2019 5:09 pm

@ef37a
A lot depends on the filtering from the inverter (if any), The power transformer in the amp will be designed to manage load current pulses, but not repetitive high voltage spikes on the primary.

I've not personally experienced such a failure, but have heard reports of them - although most commonly with cheap wall warts.
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Re: Battery powered 230VAC Inverter, safety precautions?

Postby Sam Spoons » Fri Dec 13, 2019 5:42 pm

tonyztigger wrote:unless it came out of a shop, I would just stick with branded names

I might buy off ebay, there are dozens of them on there at similar prices and ebay are usually pretty good at protecting the buyer (better in recent experience than Amazon).
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Re: Battery powered 230VAC Inverter, safety precautions?

Postby Guest » Sat Dec 14, 2019 2:01 am

Sam Spoons wrote:I might buy off ebay, there are dozens of them on there at similar prices and ebay are usually pretty good at protecting the buyer (better in recent experience than Amazon).
Very true. but you will end up weighting 2 weeeks for it to arrive then when it arrives 2 weeks later its broke and you have to pick up the return postage
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Re: Battery powered 230VAC Inverter, safety precautions?

Postby Sam Spoons » Sat Dec 14, 2019 11:11 am

Not my experience in general and, likely as not, the one that costs £90 in Halfords comes from the same Chinese factory as the £20 ebay jobbie. Just make sure you buy from a UK seller to make returning it easier if it proves unsatisfactory.
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Re: Battery powered 230VAC Inverter, safety precautions?

Postby merlyn » Tue Dec 17, 2019 7:48 pm

Sam Spoons wrote:Might still change it just to get rid of the buzz. Found this on Amazon but it looks too good to be true at that price, what do you think?

https://www.amazon.co.uk/Almencla-Power ... mp;sr=1-13

I'd think it will be better than a modified sinewave inverter. Seems like a bargain but is it too good to be true? Well, there may be corners cut, but they shouldn't affect powering a guitar amp.

First I don't believe it's 500W -- the voltage is likely to sag as the load is increased. That doesn't affect powering a guitar amp <100W.

Second the total harmonic distortion may be higher than more expensixe models, and the THD may increase as the load increases. Still, it's going to be better than the 25% THD of a modified sinewave inverter.

Cheaper inverters often don't have as good protection circuitry, but this one claims to, so that looks good.

Sam Spoons wrote:If I ever get around to doing the conversion I'll definitely install a pure sine wave inverter

* https://www.gapcb.com/products/baby-will-pcb

If you've got the skills to solder that circuit together you could consider taking AC out the circuit completely. It's possible to run the valve heaters from DC, so for that you'd need a 6.3V voltage regulator.

For the HT you'd need a DC-DC boost converter. You'd need one with the appropriate current rating but it's doable.
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Re: Battery powered 230VAC Inverter, safety precautions?

Postby Sam Spoons » Wed Dec 18, 2019 11:38 am

Yes, that was much the route I had been considering but I didn't want to mess with the VJ too much. Not sure I'll ever get around to building the 18 watt VJ much as I'd like to. I did build an Ampmaker 18 Watt kit which has been my main gigging amp for the last few years.

I've got a return address, in the UK, for the modified sine wave power pack, and they've said they will refund postage as it doesn't perform as it should. The ebay pure sine wave inverter should be here today so will check it out tonight.
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Re: Battery powered 230VAC Inverter, safety precautions?

Postby Sam Spoons » Thu Dec 19, 2019 4:15 pm

Sam Spoons wrote:Might still change it just to get rid of the buzz. Found this on Amazon but it looks too good to be true at that price, what do you think?

https://www.amazon.co.uk/Almencla-Power-Inverter-AC220V-Ports/dp/B07V63S3BC/ref=sr_1_13?keywords=pure+sine+wave+inverter&qid=1576239800&s=electronics&sr=1-13

Not sure about that one but I bought this one off ebay https://www.ebay.co.uk/itm/300W-Power-Inverter-Charger-12V-DC-To-AC-230V-Converter-Car-Pure-Sine-Wave-USB/293221255983?hash=item4445594b2f:g:5I8AAOSw0lVdd7Ph

And despite being listed as a "pure sine wave'" inverter the docs enclosed say it is a "modified sine wave" inverter so that's going back without ever being plugged in.
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