48VDC pump switch

khotton

Solar experts,

I am in the construction phase of an off-grid house in central Mexico. It took me forever to weigh the pluses and minuses of various PV solar options (12, 24, 48 V battery bank; all 120VAC, some AC and some DC circuits...). I decided for the main house it will be all 120VAC with a 48V battery bank. But for some added realiability, I felt it best to use a 48VDC water transfer pump (so if I have an inverter failure, I can still pump water).

My question is will a standard 120V AC wall switch work for a 48VDC pump (or will internal arcing be a problem)? My choices for pumps at 48VDC are limited but the Conergy Solar Slowpump model 2607 looks promising. I only need to pump about 25-feet of water head, so the pump motor is well oversized (spec. is 4.3-gpm at 160-ft of head). I have a roof-top tinaco (600Lt) with gravity fed water to sinks and bath. Actually, I will only need to transfer about 50-gallons of water per day from cistern to tinaco.

What type of power switch would you recommend? I want to minimize pump cycling (for long pump life) and felt a simple on/off switch (i.e. run pump in morning for 15-minutes to refill tinaco and then turn off) would be best and simplest. Comments and suggestion appreciated.

Thanks,
Kevin

icarus

Re: 48VDC pump switch

How many amps does the pump draw?

I use a Square D pressure switch, and was advice to de-rate it to ~10% of it's ac spec. The other simple solution is to use a Square D QO breaker of the proper size. QO breakers are DC rated for up to 48vdc. (Now that I think about it, I can't remember is QO's are switch rated, but I think they are, help anyone)

Another pump option would be something like the shureflo 9300 submersible. It will run on 24vdc so you would have to use a transformer to run it off 48vdc,

Icarus

mike95490

Re: 48VDC pump switch

Any way you can set the pump to run in the afternoon, as the solar gets the batteries into FLOAT mode ?

Switching 48V will be tough, it wants to arc. You must buy a properly rated switch or relay for it.

Lefty Wright

Re: 48VDC pump switch

If you want to operate the pump manually go to an electrical supply house and buy a "motor rated" switch. They have DC ratings and will open automatically if the pump motor is overloaded.

They have replaceable heaters which are rated for the amount of current your pump draws. You have to know the full load current rating of your pump. Just order a heater rated a little higher.

mike95490

Re: 48VDC pump switch

khotton wrote: »

What type of power switch would you recommend? I want to minimize pump cycling (for long pump life) and felt a simple on/off switch (i.e. run pump in morning for 15-minutes to refill tinaco and then turn off) would be best and simplest. Comments and suggestion appreciated.

scenario:
Get up in AM. Turn pump on. Start coffee read paper watch news about drug lords & police in a shootout, next town over. Call friends go outside, feed chickens. friends call back, military choppers overhead, watch them for a while. Eat lunch. change clothes to go into town. Whoops, clothes all wet - Pump running all morning, tank overflowed into attic.

Maybe a 15 minute timer switch ? A toilet tank style fill valve ? Overflow drain to outdoors ?
Exer-cycle style water pump for backup :
http://www.edc-cu.org/ppt/WheelDeal.pdf
http://www.gilgnet.com/docs/Bicycle_pump_disclosure.pdf