Managing Inverter In-Rush
Managing Inverter In-Rush
(OP)
I've built a cute little solar fountain- I love the sound of running water, and it complements my wife's award-winning front garden nicely I think- she was lukewarm at first but I think she's grown to like it too, but then again she's always been a tough audience for any of my projects- even the ones she "directs"...
Anyway, the original build started out with a nice simple option for the pump: a little 500 gph 12VDC boat bilge pump. I didn't expect it to last long, but of course they're cheap too. Regrettably, it failed after a couple months of 4-8 hr/d operation, which is obviously too quick.
DC pumps are expensive for some reason, and I'm chronically cheap. I bought a very small brushless DC pump as a test unit, and it too failed- even faster than the bilge pump.
So- the option seems to be 120VAC pond pumps, which are a dime a dozen, offered with warranty, and available at the local Home Despot. I bought one, and found it runs quite well on a little 400W inverter I had laying around. But regrettably, the inverter has a huge inrush current, likely to charge the input caps. While it works just fine when connected directly to my solar-charged deep cycle FLA battery, when connected to the load protection output of my charge controller, the inrush trips the overcurrent protection on the charge controller.
The charge controller I'm using is this one from Morningstar:
https://2n1s7w3qw84d2ysnx3ia2bct-wpengine.netdna-s...
The 10A 12V version.
My original strategy had a 12V timer turning the pump on and off at the right times of day, so it runs for enjoyment when people are around but shuts off at night and during a couple periods during weekdays to give the solar panel a chance to top up and balance the battery. The timer has contacts which are rated for AC, so I can use it on the output side of the inverter. But the problem is how to start up the inverter in the first place? Any time we get a string of dark days in a row and the load control feature of the charge controller kicks in to protect the battery from over-discharge, I'd end up with the inrush problem when it re-starts.
So far, the only idea I've had is putting a pre-charge resistor in series with the inverter inlet. The inverter draws about 2A at 12V when running the pump, and I have to keep the inrush below 10A to keep the charge controller happy. I'd likely have to put a time delay relay in parallel with this resistor to short it once the precharge is done, otherwise I'd be running the inverter at too low an input voltage for it to be happy. But of course the time delay relay is another component and more bother.
Any other suggestions on how to handle this would be welcome!
Anyway, the original build started out with a nice simple option for the pump: a little 500 gph 12VDC boat bilge pump. I didn't expect it to last long, but of course they're cheap too. Regrettably, it failed after a couple months of 4-8 hr/d operation, which is obviously too quick.
DC pumps are expensive for some reason, and I'm chronically cheap. I bought a very small brushless DC pump as a test unit, and it too failed- even faster than the bilge pump.
So- the option seems to be 120VAC pond pumps, which are a dime a dozen, offered with warranty, and available at the local Home Despot. I bought one, and found it runs quite well on a little 400W inverter I had laying around. But regrettably, the inverter has a huge inrush current, likely to charge the input caps. While it works just fine when connected directly to my solar-charged deep cycle FLA battery, when connected to the load protection output of my charge controller, the inrush trips the overcurrent protection on the charge controller.
The charge controller I'm using is this one from Morningstar:
https://2n1s7w3qw84d2ysnx3ia2bct-wpengine.netdna-s...
The 10A 12V version.
My original strategy had a 12V timer turning the pump on and off at the right times of day, so it runs for enjoyment when people are around but shuts off at night and during a couple periods during weekdays to give the solar panel a chance to top up and balance the battery. The timer has contacts which are rated for AC, so I can use it on the output side of the inverter. But the problem is how to start up the inverter in the first place? Any time we get a string of dark days in a row and the load control feature of the charge controller kicks in to protect the battery from over-discharge, I'd end up with the inrush problem when it re-starts.
So far, the only idea I've had is putting a pre-charge resistor in series with the inverter inlet. The inverter draws about 2A at 12V when running the pump, and I have to keep the inrush below 10A to keep the charge controller happy. I'd likely have to put a time delay relay in parallel with this resistor to short it once the precharge is done, otherwise I'd be running the inverter at too low an input voltage for it to be happy. But of course the time delay relay is another component and more bother.
Any other suggestions on how to handle this would be welcome!





RE: Managing Inverter In-Rush
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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Managing Inverter In-Rush
When doing installations, one of the tools I made for charging the large input capacitors used in inverter and UPS systems, or for final checks before making connections in high energy storage 48VDC plants, was a small tool that used a 120VAC 100w halogen lamp and also had a 12VDC 55 watt halogen lamp. This device was used to first close the circuit using these "resistors", then if all is well, then make the circuit connection.
A time delay relay (a simple rc circuit driving the relay coil could do that) to start the inverter with the resistor in series, then relay shunt it out of the circuit would suffice.
Halogens may or may not work for you or, you if you use them, may need to experiment with the wattage rating, as their cold filament resistance is very low.
RE: Managing Inverter In-Rush
Bill
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"Why not the best?"
Jimmy Carter
RE: Managing Inverter In-Rush
DanEE- thanks for the suggestions- they're very helpful. I have a bunch of big wirewound resistors to choose from, which will do just fine I think, but only with the relay. If I use a normally open contact on the relay I guess I could use an RC circuit on the coil, probably with a time constant of a half second or so- will take some experimenting. When I've tried that strategy before I got an annoying buzz out of the relay as the RC circuit charged up, but this delay is so short that it may not be such a problem. Fortunately at least this inverter re-starts after its input is interrupted without having to go and push the "on" button again, and its on-state loss with no load is pretty minimal, so I'll likely put the timer on the AC side of the inverter rather than having to pre-charge it every time the timer for the pump turns on.
RE: Managing Inverter In-Rush
You get a virtual LPS for that one, and a virtual drink in the Pub too!
RE: Managing Inverter In-Rush
Dan - Owner
http://www.Hi-TecDesigns.com
RE: Managing Inverter In-Rush
You could try just adding a hundred feet of extension cord between the charge controller and the inverter. That worked for a friend of mine trying to start wood working equipment from his generator. Just added enough resistance to slow the rush.
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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Managing Inverter In-Rush
Did I miss that 65A inrush capacity on the spec sheet? Typical...
I haven't measured the inverter inrush except by observing the spark you get when you connect the input alligator clips to the terminals of the battery, which is surprising, though that's typical with DC circuits...It's a 400 W inverter driving a 25 watt motor, but the inverter I have is FREE (picked up at random at a different garage sale a few years ago), so I'll try to make it work. It's a little Chinese toy of a thing, but does have an internal fan which doesn't even bother to turn on to run this 25W motor load. I'm not sure whether or not the 75W toys that you can buy to plug into your car cigarette lighter would even start the little (presumably) shaded pole motor in the pump.
RE: Managing Inverter In-Rush