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Author Topic: small 12v inverters  (Read 1843 times)
chasfromnorfolk
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« on: April 25, 2020, 10:47:01 AM »

Hope someone might help pass the lockdown time: I have a 240v electric ram - maybe off a tilting chair - rated at 160w bought at a car boot sale 20 years ago in case it came in handy.
I’m housing some rescue hens in my polytunnel and think I can rig the ram + car battery + solar panel + timeswitch to open the door enough for the hens to let themselves out in the morning.
I see plenty of cheap inverters on eBay - is there any point in getting one over-rated beyond 160w to provide a ‘cushion’ or would, say, a 300w one just suck more from the battery?

Cheers,
Chas
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kdmnx
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« Reply #1 on: April 25, 2020, 10:53:55 AM »

You absolutely DO need to over-rate the inverter!

For several reasons:
  • Those cheapo inverters straight out lie about their capacity. Usually by a factor of 2.
  • That "ram" is likely to be an inductive load, therefore it'll draw a large amount of power on startup, you usually need to overspecify components such as inverters by a factor of 4 for an inductive load.

For this application, I'd buy an inverter that has 1200-1500W written in big writing on the box.

(It might be easier to buy a 12V ram.)
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12x JA Solar 340Wp panels (total 4080Wp)
Lux Power inverter charger
5x PylonTech 2000 2.4kWh batteries (total 12kWh (11kWh usable))
biff
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« Reply #2 on: April 25, 2020, 01:47:51 PM »

Hi Chas,
           Silverline do a 300watt modified sine wave for £50,00. Argus and Screwfix inverters are not bad. To be honest, you really don,t go by the money but by the humour the Chinese workers are in when they stick them together, There is a small    95mm x 55mm x 15omm approx, jobbie marketed under about a dozen different namesm It is genreally silver in colour with black writing on it, it comes in both 12v and 24v. I fount the 24v version outstanding and gave years of use. I never got much feedback on the 12v version but for the size of the 24v one (the two were the same size) it really performed very well. They were alarmed and with dual sockets, I know,, not a lot of room foe one socket never mind two but they worked well. Modified of course.
 So If you look out for those measurements,( ijust checked them) You could try for one of them for about £25 to £35.
                                    Biff
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Scruff
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« Reply #3 on: April 26, 2020, 05:52:15 AM »

You absolutely DO need to over-rate the inverter!

For several reasons:
  • Those cheapo inverters straight out lie about their capacity. Usually by a factor of 2.
  • That "ram" is likely to be an inductive load, therefore it'll draw a large amount of power on startup, you usually need to overspecify components such as inverters by a factor of 4 for an inductive load.




Amen!  signofcross

For this application, I'd buy an inverter that has 1200-1500W written in big writing on the box.


Or go 2X low frequency.

We all now mod sine is marketing for inverting square right? Terrible for induction motors...run! horror
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chasfromnorfolk
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« Reply #4 on: April 27, 2020, 10:38:52 AM »

Thanks, All, for the imput, if I progress I’ll report back - but it sounds like one of those jobs to put back in the list...

Chas
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