How to limit DC water pump inrush current

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Re: How to limit DC water pump inrush current

Postby karrak » Thu Jan 26, 2017 12:52 am

tom rickard wrote:This pump is the supply to the evap. airconditioner (not the internal pump that circulates water through the pads). It essentially pumps water until it is stopped by a float valve. The airconditioner constantly uses a small amount of water, so the pump cycles often but for a very short time.


I have a 240VAC to 24V Meanwell supply. The adjustment for my unit and looking at the diagram for your supply should be between the screw terminal and the power on LED. It might be worth trying the pump with the lowest voltage that the supply will put out to see if it will work.


Regarding the short run time. It might be worthwhile putting in a delay timer that would delay the pump restarting for whatever time it takes the evap cooler to say half empty the tank.

Is the motor power wired directly through the float switch, if so is it rated to handle the 30+ amps of inrush current?

I'll try fitting a battery inline,


When you say inline I assume you mean in parallel with the power supply. It might be worth putting a 30A fuse from the + terminal of the battery.

Simon

Simon
Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
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Re: How to limit DC water pump inrush current

Postby karrak » Thu Jan 26, 2017 8:21 am

Another thought.

If the only problem with your old pump is the pressure switch, can you disconnect the pressure switch and replace it with the float switch and timer or maybe get a replacement pressure switch?

Actually, If the pressure switch is stuck on you don't even need to remove it, just put the float switch/timer inline between the power supply and the pump motor

Simon
Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger https://github.com/simat/BatteryMonitor
Latronics 4kW Inverter, homemade MPPT controller
karrak
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Re: How to limit DC water pump inrush current

Postby tom rickard » Fri Jan 27, 2017 8:41 pm

Thanks for the good thoughts..

The float valve is a mechanical valve. In effect the pump behaves as if it is hooked into a system with a slightly leaking tap. Also the A/C is 25meters away from the pump and power supply, so to replace it with an electrical float switch and run the wiring back to the pump is probably harder for me than to install my header tank!

The faulty pump is an ebay special that cost me $25, not really worth messing around with.

I did mean to put the battery in parallel across the terminals of the pump. I will have a play tomorrow with firstly reducing supply voltage, then installing a battery. I'll report back with my findings.
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Re: How to limit DC water pump inrush current

Postby tom rickard » Sun Jan 29, 2017 9:49 pm

Hi. I found the voltage adjustment pot, turned it down to 11.5V, and the supply now runs the pump. It still cycles very often though, so I think in any case it will be a good idea to just go with a header tank and gravity feed.

Thanks so much for your assistance.
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Re: How to limit DC water pump inrush current

Postby karrak » Sun Jan 29, 2017 10:51 pm

Hi Tom,

I assume that the new pump also operates via a pressure switch?

Rather than putting in a header tank which I assume would need float switches to start and stop the water going into the tank and a pump how about using your current setup but with a delay timer something like this one http://www.ebay.com.au/itm/DC-12V-LED-Display-Digital-Delay-Timer-Control-Switch-Module-PLC-Automation-GU-/351543112127?hash=item51d99a31bf:g:x5EAAOSwKsRWFgcD. This would have to be hooked up to a more powerful relay.

Another option might be a pressure tank. Do you have any old gas cylinders lying around?

I am puzzled. There must be some reason why you aren't hooking the evap cooler up to your house water supply?

Simon
Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger https://github.com/simat/BatteryMonitor
Latronics 4kW Inverter, homemade MPPT controller
karrak
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Joined: Wed Jan 21, 2015 1:14 am
Location: Cookernup (near Harvey) SW Western Australia

Re: How to limit DC water pump inrush current

Postby tom rickard » Wed Feb 01, 2017 5:22 pm

Probably should have mentioned that we don't have mains water, I don't want to cycle our 240V pump, but thought the DC pump would handle it OK. The header tank i'll set up will fill via a timer tap on our outside tap, and when full it will overflow back into the tank it's coming from. The pump might run for an extra 5 mins or so, but we have plenty of power in summer.

I try to keep things as simple as possible, to operate, and also maintain. I have seen quite a few off-grid set-ups where if you weren't the one that installed it, you'd have no hope of operating the house. I like the idea of electronic gadgetry and controllers, but when they fail (and they all eventually do) it can be a pain. When I've finished the water supply to our evap air conditioner, anyone will be able to see how it works.

When I build my new house, i'll use reverse cycle airconditioning and an external vent system, and do away with evap aircon altogether.

The same goes for off-grid power. I know of a system here in SA where it was professionally installed, and it is a nice system with good components, but his installer retired, and he had a minor issue with the system and couldn't find an electrician that would touch it with a barge pole!
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