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Post by johngalt on Aug 8, 2021 20:00:17 GMT 10
Hi I've just been going through my water security plan. I live on a generic suburban block in a major capital city so not rural or anything. My main store of water is a 500L rain water tank, I'm planning to add either a 3kL or a 5kL rain tank in the near future. I had planned to use my garden bore as a supplemental water source to top off the tanks, the water is more than clear enough with just a hint of sulphur smell and a bit of iron, Any drinking water will be filtered using an RO system anyway.
The main problem I see is running the pump during a power failure, the pump is a single phase 1100 watt (8.1A running) unit down about 50 meters however the spec sheet says the starting current is 4.2 times running, that puts it at about ~6500 watts (34 A), mind you that's only for a fraction of a second during startup.
I have this chunky old Honda generator from the 80's that would start it but running a generator during grid down would attract a lot of attention plus the ongoing petrol requirement so I would rather not use that path.
The other idea I had was a solar pump controller, they do make them and I have enough panels for it but it's almost $2k for the unit for something I may possibly never use.
The 3rd idea I had was using a Lithium solar power brick like the Bluetti however inverters suck at starting motors plus the peak instantaneous load is only 4800 for a fraction of a second then back to 2200 watts. I do like the idea of the lithium pack as it would also power other appliances around the home as well as being able to take it away camping so it would have multi uses.
So my question is this: Has anyone ever used one of those ebay soft starters to reduce inrush current of starting motors or have any other ideas on how to silently run a power hungry bore pump?
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Deleted
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Post by Deleted on Aug 8, 2021 20:31:38 GMT 10
Im assumning this is a submersible pump at the bottom of the bore in which case I would be concerned the actual current draw may be higher than the spc due to volt drop in the smallish cabling typically used on bore pumps. Get an AC clamp meter and check the actual current draw when running so you know exactly your current draw is. If you have access to a decent high speed electrical data recorder you can trend the start and then you will know how much your start current is and for how long. With this info you can then look at at alternative power sources that can supply what you need.
You may be better to ditch the current pump and replace with a DC pump and solar converter. A search of ebay for solar bore pump shows plenty of options at relatively low cost although I have no experience with these products myself
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malewithatail
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Post by malewithatail on Aug 9, 2021 10:10:08 GMT 10
Previous to modern power semi conductors, the usual way to "soft start" a drive was to do star/delta starting if 3 phase, or reduced voltage starting using an inductor or capacitor arrangement to reduce the inrush current. Nowadays, with the cheap and easily available IUGBT's and SCR' etc available, the modern soft starter is a reliable device. I have used a soft starter to get away a 2.7 kw water pump on a 3 kw inverter, and it works. It wasn't a bore pump, but the principle is the same. Some modern bore pump motors are already powered from a controller as they are a dc type 3 phase motor, kind of like a high power stepper motor and a external soft starter wouldn't work with that type.
In 2012 Silicon Chip magazine published a simple soft starter based on a thermistor to reduce starting current. You should be able to get a copy of it through the publishers. I have a copy of the actual circuit, but not of the whole article. Also, Jaycar has a power tool soft starter kit, number KC-5511, but that is for universal type motors with commutators, like drills and saws. It should work with an induction motor though I haven't tried it yet. (There is a KC-5511 kit on my bench I was given as it didn't work, but I'm not sure weather that was because of the operators not understanding just what it was supposed to do, or if its actually faulty).
In any case, next weekend I will investigate weather the kit is faulty and try running a house type water pump and let u know.
By the way, these kits are relatively simple to assemble, and soldering is a good skill to have anyway.
Solar arrays and pumps are cheap now and they work really well, especially in the smaller sizes for domestic use. The solar array does tend to stand out though. I've installed quite a few of late and was surprised just how efficient modern submersible pumps are. They will start pumping, very slowly, nearly at dawn, getting more flow as the sun comes up. Even in overcast weather, they will still pump something.
Experience is a good teacher, but her fees are high.
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Post by johngalt on Aug 13, 2021 17:03:17 GMT 10
I've just measured the current draw of the unit, I don't have anything fancy just a Japanese clamp meter made in the late 90s, no peak hold so all these values are running current. With high flowing water (Hose tap open) 6.8 Amps With all valves closed (Dead headding) 5.0 Amps Funny I didn't expect the amps to drop the less water was flowing. Must be activating the bypass valve at the pump. I was thinking of getting one or two of these units and mounting it up in a box ready to go should I need it. Altronics seem to have a kit but there are no specs on it and doesn't quite look like what I need. Jaycar had something but discontinued. www.ebay.com.au/itm/284307854694?var=585811012101I didn't really want to rip and replace the pump with a solar pump plus I would have no way of getting 38m of water filled 40mm poly up to the surface by myself to change the pump, plus don't want to be undertaking that sort of work during grid down. I might also have to start the pump with all valves closed to reduce current then slowly open the valve to the water tanks, once running it can run for hours to fill the tanks and I'm thinking it might be once a week task depending on water use. |
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malewithatail
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Post by malewithatail on Aug 14, 2021 10:12:13 GMT 10
Pump operates more efficiently when not dead heading, less friction loss as well, hence the lower amps running.
Induction motors, like the standard Davy water pump besides a house tank, need between 5 and 10 X the running current to start, depending on the pump design, pipe lengths etc.
Its not good practice to start a pump dead headed, ie outlet closed off, the pressure can build very quickly and burst the pump casing, happened to me last weekend at a fire when the captain quickly closed off the nozzle on the portable pump and the sudden pressure buildup split the pump casing from top to bottom. Its an understatement to say I got wet !
For $ 110, try it, if it doesn't blow up at first try, it will probably be ok, then get a spare. Only thing is the description of a fan in the top. Fans start on a very light load and build up as the speed increases, pump do too, but water isn't as compressible as air is.
Faster than a speeding ticket !
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