DC pump for 24 or 48v?

[Loner]

I am moving an RV onto some land I purchased. The RV will be powered by solar. The RV is setup for 12v but my power needs are more than a 12v system will provide so I plan to go with 24v or maybe even 48 since the RV is temporary anyway until the house is built.

Since the lights and water pump are 12v they are of no use on the higher voltage system unless I use a converter and that doesn't seem worth it since the RV is temporary. I need to be able to run a water pump off the higher voltage system. The water will be pumped from a 1000 gallon water tank that sits on grade so there isn't much lift. Can you recommend a good DC pump that can be used on 24 or 48v (haven't seen any for 48v)? I considered a pump that runs off A/C but would prefer to stick with a DC pump if possible.

[Naptown]

Shurflo and other make them.
No personal expperience.

[SummersWood]

Diaphragm type pump experience

The Shurflo type diaphragm pumps are a great work horse for your type of application:

The water will be pumped from a 1000 gallon water tank that sits on grade so there isn't much lift

They require about 75W for good enough house pressure at reasonable flow rate 30 psi and 10 lpm.
If you need higher flow rates, use paralleled pumps. They have a great 2.5m / 8 ft suction.

My system in operation for 9 years consists of a Shurflo 2088 24VDC mounted onto an 12 liter pressure accumulator tank.
This tank is absolutely required as the pump is the simplest type with a simple on/off pressure switch.
It has no fancy electronics for constant pressure/flow, those types have a phantom load on all the time.
Much better/cheaper is the simplest type with simple on/off pressure switch.

Now the one thing that I dislike about this pump is the failure rate of the pressure sensing microswitch
that turns the pump on/off. The microswitch is not available as a cheap repair item, but there are part kits to repair
the pump that are about half the price of a new pump because they include half a new pump: the pump head with switch.

Microswitch failure bit me in year 3 of 9 and I had to buy a new pump head. As I keep a spare unit for every pump (once qualified)
in our off grid home, I had a new Shurflo pump ready to swap in when the microswitch started failing.
The failure mode is the pump "chattering" as it reaches shut off pressure, rapidly cycling on/off.
This rapid open/close cycle of the microswitch with moderate current DC overheats their small contact area and the contacts burn out.
The pump is however still quite useable for a few weeks/months so this "pump chatter" is an audible indication of a slow failover mode.

My fix was simple electronics 101: a 24V auto headlight relay (BOSCH N/O) and a diode and a capacitor.
The microswitch now controls the low current to the relay coil, the relay switches the high current of the pump motor,
the capacitor (50V 1000uF) keeps the relay coil active and the pump operating for about one second after pressure opens the microswitch
thus driving the pressure passed the hysteresis ("chatter") point so the pump shuts off cleanly.
The diode protects the contacts from feed back of relay's coil field collapse current. Works dandy for many years.

Also diaphragm pumps are very noisy. But this is a feature as you will notice the pump turning on at a regular cycle
indicating a small water leak such as a seeping toilet cistern.
Lastly, you will need an inlet filter to protect the pump from grit.

[jon_r]

I have a Shurflo 120VAC pump wired directly to 4 small panels in series. This powers a plant irrigation system.

Note that the panels only add up to about 75V, but it works fine because while the pump is labeled AC, it is actually a DC motor. I think that the pump will last longer than if I operated at full voltage. At 10 hours/day, 365 days/year, this is a real concern.

[russ]

I have a Shurflo 120VAC pump wired directly to 4 small panels in series. This powers a plant irrigation system.

Note that the panels only add up to about 75V, but it works fine because while the pump is labeled AC, it is actually a DC motor. I think that the pump will last longer than if I operated at full voltage. At 10 hours/day, 365 days/year, this is a real concern.

BS - that stands for bull ****! You just made the statement that an AC motor and a DC motor are the same. Where do you get the 10 hours of sunlight in Michigan?

[inetdog]

BS - that stands for bull ****! You just made the statement that an AC motor and a DC motor are the same. Where do you get the 10 hours of sunlight in Michigan?

1. If the motor is a "universal" motor (that is a series, parallel or compound wound field motor with commutator and brushes) it will run equally well off DC or AC.
In that case the motor may be labelled for AC input at a particular voltage, but not actually be an AC-only (induction) motor. It will work off DC, although possibly at a different voltage.

So although what jon_r said could be confusing to some, that particular part of what he said is not necessarily BS.

2. Under a sunlamp maybe? You might be able to see a pump run for a total of 10 hours, but several hours on the start and end of the curve will not be moving much water.

[bcroe]

Fix

Microswitch failure bit me in year 3 of 9 and I had to buy a new pump head.

My fix was simple electronics 101: a 24V auto headlight relay (BOSCH N/O) and a diode and a capacitor.
The microswitch now controls the low current to the relay coil, the relay switches the high current of the pump motor

Its hard to believe, the company hasn't responded with an upgrade, to such an
obvious fault, and a similarly obvious fix. Maybe they like selling more pump heads.
Bruce Roe

[ZoNiE]

Its hard to believe, the company hasn't responded with an upgrade, to such an
obvious fault, and a similarly obvious fix. Maybe they like selling more pump heads.
Bruce Roe

They Do.


The pumps also chatter when you use a pressure tank in the system, as I have learned recently...

[mapmaker]

If the motor is a "universal" motor (that is a series, parallel or compound wound field motor with commutator and brushes) it will run equally well off DC or AC.
In that case the motor may be labelled for AC input at a particular voltage, but not actually be an AC-only (induction) motor. It will work off DC, although possibly at a different voltage.

Tech support told me that the AC is rectified. The brushes transmit DC.

They also told me that if I opened up the motor on my 120 volt AC shurfo (failed after 250 hours), it would be the negative brush that was worn out. It was. The technician assured me that the higher the DC voltage, the faster the brush wears out. The brushes on the 12 volt DC pump last the longest.

--mapmaker

[inetdog]

That makes a lot of sense, since there is a momentary arc as the brush passes across the copper commutator segments. Whether the copper or the brush is most eroded by the arc will depend on the direction that the current is flowing.

Maybe you should swap the two brushes occasionally the way you rotate tires to even the wear?

[ZoNiE]

That makes a lot of sense, since there is a momentary arc as the brush passes across the copper commutator segments. Whether the copper or the brush is most eroded by the arc will depend on the direction that the current is flowing.

Maybe you should swap the two brushes occasionally the way you rotate tires to even the wear?

THAT is a good idea...

[mapmaker]

THAT is a good idea...

Did you notice the font that inetdog used to write that "good idea"? His choice of font means something.

--mapmaker

[inetdog]

Did you notice the font that inetdog used to write that "good idea"? His choice of font means something.

--mapmaker

Perhaps my use of the "sarcasm font" was a little overstated.
Depending on the work required to interchange the brushes versus the cost of replacement brushes, and taking into account whether the two brushes are mechanically compatible along with the time required for any brush to wear into a new location, it might actually make sense. But I did not want to make it seem like an unconditional recommendation, just an idea for exploration.

[bcroe]

Perhaps my use of the "sarcasm font" was a little overstated.
Depending on the work required to interchange the brushes versus the cost of replacement brushes, and taking into account whether the two brushes are mechanically compatible along with the time required for any brush to wear into a new location, it might actually make sense. But I did not want to make it seem like an unconditional recommendation, just an idea for exploration.

For motors not using permanent magnets, it might be easier to reverse the power leads. Bruce Roe