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Semi-Diy 12V To 240V Sine Wave Inverters?


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#1 jsharris

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Posted 10 January 2016 - 08:05 PM

I've been looking around for one or two low power inverters, for a couple of battery back up ideas I have (as an alternative to having a generator).

The basic idea is to use a bit of spare excess PV to keep a modest battery bank charged up on standby, then, if we get a power cut (all too frequent around here) I can use the battery bank, via the inverters, to power one or two low power essential things.

I've read far too many tales of Chinese inverters being unreliable, unsafe and under-rated, yet I don't want to spend a fortune on something that appears to be non-Chinese, but is really just wearing a thin disguise.

Whilst looking around on that well-known auction site I've come across masses of inverter kits from China. Knowing that Chinese basic electronics is often OK, but that poor assembly, quality control and a complete disregard for safety are the reasons for their failure, I've been wondering if anyone here has looked at these kits and built one up?

This is the sort of thing I've been looking at: http://www.ebay.co.u...HQAAOSwJkJWjhzX

I doubt it's really anything like 1000 W, but as I could build it into a decent case, with proper heatsinking and circuit protection, it seems a pretty cheap way to get a sine wave inverter. Sadly I can't find anything about them from a brief bit of web searching, but the basic components look reasonable, as does the way it generates a PWM sine wave.

#2 SteamyTea

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Posted 10 January 2016 - 08:12 PM

I mentioned somewhere about connecting a couple of cheap inverters together (think it was about generators).

If you got a couple cheap 1 kW sine wave inverter, how hard would it be to hack into them and connect them up so they are in phase.

All I want to do is run a 2 kW load for an hour or so (water heating) and an induction hob (not at the same time as water heater).

#3 jsharris

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Posted 10 January 2016 - 08:18 PM

It shouldn't be hard to get several inverters phase synced if they are built from kits like this, as it should be possible to run them from a common clock.

#4 SteamyTea

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Posted 10 January 2016 - 08:24 PM

Good. I thought it should be fairly easy. If opening up the boxes anyway, should be easy enough to improve the cooling as well. And probably a better capacitor (as they always seem to fail).

Alternatively, if something is not grid connected, how hard would it be to build from scratch, not as if the frequency has to be spot on, so could spend the money on making the wave better and the efficiency much better when at low loads.
Mind you at £23.50, not worth getting the tools out for.

Edit:
Just noticed you have to get the tools out.

Edited by SteamyTea, 10 January 2016 - 08:30 PM.


#5 jsharris

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Posted 10 January 2016 - 09:40 PM

The price is the main reason for me looking at these. The hard to do stuff (the PCB etc) is done, so building it into a decent housing, upgrading the capacitors for decent ones, putting a decent amount of safety protection in etc, is relatively cheap, plus you end up with something that's pretty much a known entity, rather than the very much unknown of a Chinese no-name product. If you hunt around there are all sorts of variants of these kits, so with a lot more quoted power (BUT, they probably only make half their rated power..............).

#6 Alphonsox

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Posted 10 January 2016 - 09:45 PM

Wouldn't a second hand UPS from ebay suit the bill ? There always seem to be loads available due to companies throwing them out rather than replacing the batteries.

#7 SteamyTea

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Posted 10 January 2016 - 09:48 PM

Shall have to think about this, almost seems worth a 100 quid punt to see what can be cobbled up.

Or just try out one of these at 85 quid
http://www.ebay.co.u...nQAAOSw~gRVyd9z

#8 jsharris

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Posted 10 January 2016 - 09:59 PM

View PostAlphonsox, on 10 January 2016 - 09:45 PM, said:

Wouldn't a second hand UPS from ebay suit the bill ? There always seem to be loads available due to companies throwing them out rather than replacing the batteries.

I looked at them, but they aren't usually pure sine wave, often they have a pretty crude square wave, or modified square wave, output that is fine for running a SMPS in a computer, but not good for running anything like a 35W induction motor on a small air pump.

#9 jsharris

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Posted 10 January 2016 - 10:05 PM

View PostSteamyTea, on 10 January 2016 - 09:48 PM, said:

Shall have to think about this, almost seems worth a 100 quid punt to see what can be cobbled up.

Or just try out one of these at 85 quid
http://www.ebay.co.u...nQAAOSw~gRVyd9z

Modified sine (really just a sort of stepped square) wave should be fine with a resistive load, so perhaps worth a go. It's the safety and internal mechanical build quality that bothers me with this stuff, though. The Chinese seem to have a cavalier disregard for human life when they build electrical stuff, so before using something like that I'd want to take it apart and do a lot of checks on the build quality, earthing component heat sinking, capacitor ratings, EMI protection etc. If going that far it makes sense (at least for me) to build from parts, as that way I can be pretty confident that it'll be safe and less likely to wipe out all the radios for a few hundred yards around. Also, as above, I need a pure sine inverter to run induction motors OK.

#10 DamonHD

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Posted 10 January 2016 - 10:14 PM

JSH: this is the sort of thing worth asking about over at fieldlines.com where people regularly build inverters, etc. There was a long thread recently where someone had to give up their (bananas behaviour) SMA inverters and do something similar to your proposal.

Rgds

Damon

#11 jsharris

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Posted 10 January 2016 - 11:04 PM

Thanks Damon, I'll pop over there and have a look see.