12V water pump circuit

Submitted: Wednesday, Dec 16, 2015 at 19:46
ThreadID: 131145 Views:2029 Replies:10 FollowUps:8
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Building my own small caravan as seen on a few threads here.

Am having only 12V power. Have two water outlets, a cold water sink and a cold shower. Hot water from a solar bag.

Got a 44 litre black water tank installed. Got a 12V pump off that then a blue pipe 10mm to a "T" junction. One goes to a normally off solenoid 12V then to the shower. The other to a normally off solenoid to the sink.

For the life of me I cant work out the wiring circuit. Both the shower and the sink on/off switches have two poles only.

I have two cables from the pump area to the fuse box each with 2 cables eg two x a double cable so I can use two circuits one for each line. But I want to avoid a 24V spike if both switches are turned on the same time.
Hope you people can help out.
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Reply By: HKB Electronics - Wednesday, Dec 16, 2015 at 20:15

Wednesday, Dec 16, 2015 at 20:15
Generally the switches are wired in parallel, positive to the switch then
to the pump, earth on the other side of the pump, pretty simple.

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AnswerID: 593881

Follow Up By: eaglefree - Wednesday, Dec 16, 2015 at 21:03

Wednesday, Dec 16, 2015 at 21:03
Thanks HKB. I'm familiar with that basic wiring circuit. But what happens when you include two solonoids one on each tube i.e. one to the sink and one to the shower? How do you have the pump going on the shower and not going on the sink? Hope I've explained it well.?
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Reply By: HKB Electronics - Wednesday, Dec 16, 2015 at 21:59

Wednesday, Dec 16, 2015 at 21:59
Generally most use taps with switches in them, the water will only run through the tap
that is open.

If you don't have taps as such then you would need to run from the switch to the
solenoid then from the solenoid to the pump through a suitably rated diode. The diodes
will prevent the positive feedback to the other solenoid.

Another option would be to use a relay with a changeover contact, one switch operates
the solenoid and through the break contact to the pump.

The other switch operates its solenoid and the relay and connects to the make contact
of the relay.

The pump is connected to the lever spring contact.

Principle of operation is switch one operates its solenoid and through the realy the pump.
Switch two operates its solenoid and the relay and through the relay to operate the pump.

Hope that makes sense.

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Reply By: Peter_n_Margaret - Wednesday, Dec 16, 2015 at 22:01

Wednesday, Dec 16, 2015 at 22:01
Taps are pretty reliable :)

Cheers,
Peter
OKA196 Motorhome.
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Reply By: kgarn - Wednesday, Dec 16, 2015 at 22:22

Wednesday, Dec 16, 2015 at 22:22
Perhaps you could try something like this.
The pump will turn on when either switch (or both) is closed, but closing a switch will only open the associated solenoid, and not the other.

Ken



AnswerID: 593885

Follow Up By: kgarn - Wednesday, Dec 16, 2015 at 22:27

Wednesday, Dec 16, 2015 at 22:27
NB.

I should add that the diodes would have to be appropriately rated to carry the pump current !

Ken
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Follow Up By: eaglefree - Wednesday, Dec 16, 2015 at 23:14

Wednesday, Dec 16, 2015 at 23:14
Thanks Ken and the effort you put in.

Funny enough this whole process would have been cheaper and simpler if I'd purchased two pumps in the first place and had two totally separate systems with a "T" piece at the tank outlet. Fittings, solonoids etc - a second pump on ebay is cheaper lol

So I thank you all for your time but this electrical business is all too much for my brain cells to cope with. So a second pump will be the way I'll go.

Cheers Tony
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Follow Up By: Roachie Silverado - Thursday, Dec 17, 2015 at 05:59

Thursday, Dec 17, 2015 at 05:59
And you needn't fear a 24v spike if both switches are on at the same time.

You cannot deliver 24v to the motor if the supply is only 12v, regardless of how many switches you have turned on (unless you have a voltage converter/transformer of course).
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Reply By: kgarn - Thursday, Dec 17, 2015 at 08:51

Thursday, Dec 17, 2015 at 08:51
If you are trying to minimise weight then keep in mind that adding a second pump will add perhaps up to 2kg.
If you use the single pump configuration and use one half of a bridge rectifier as shown below then you would only add ~ 20g, however you may need to mount the device on a small heatsink.
The cost of the rectifier as shown is only $5.50 at Jaycar.

As shown in the diagram, only one half of the bridge is used, but the package is convenient and easy to use and mount..

Ken


AnswerID: 593889

Reply By: pop2jocem - Thursday, Dec 17, 2015 at 10:04

Thursday, Dec 17, 2015 at 10:04
Maybe I am missing some important detail here, has been known to happen (;=)) but wouldn't a pressure controlled pump such as a Sureflo as used in most vans be a much simpler way out. Just an isolating switch between the battery and pump.
Either tap being turned on causes a pressure drop and activates the pump. Turn the tap off and the restoration of pressure switches the pump off.

Cheers
Pop
AnswerID: 593890

Follow Up By: vk1dx - Thursday, Dec 17, 2015 at 11:00

Thursday, Dec 17, 2015 at 11:00
It kind of makes sense, what you say Pop. However, we had a pressure sensitive pump in the old Chesney and the tube to the sink developed a leak and we lost all the water. Luckily we were in a populated area. I chose to add a pressure controlled pump to the tank in the 4WD for just that reason as we nearly always are remote and solo to boot.

Both sides have merit and I would prefer to play it safe.

Maybe our OP has the same idea.

Phil
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Follow Up By: pop2jocem - Thursday, Dec 17, 2015 at 11:45

Thursday, Dec 17, 2015 at 11:45
You're dead right Phil about the possibility of a leak causing a loss of your precious water supply which is why I suggested an isolating switch between the battery and the pump. We always turn that switch off if we are leaving the van to go exploring. If in a caravan park we turn the supply tap off in case the leak happens in the same circumstances and worse if the leak is in the internal plumbing (:-0

Cheers
Pop
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Follow Up By: HKB Electronics - Thursday, Dec 17, 2015 at 11:57

Thursday, Dec 17, 2015 at 11:57
I have similar in my Vista, cold water taps have inbuilt switches, hot water I added
has pressure pump, both pumps have master switch which we leave turned
off when not using the taps.

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Reply By: Member - Rosco from way back - Thursday, Dec 17, 2015 at 10:18

Thursday, Dec 17, 2015 at 10:18
With all due respect, aren't you over complicating the issue. Why not use a single pressure pump configuration?
AnswerID: 593891

Reply By: eaglefree - Thursday, Dec 17, 2015 at 12:22

Thursday, Dec 17, 2015 at 12:22
thanks again.

Last night I ordered another pump...$29 including postage.

From a "Y" fitting from the tank the systems will be totally separate. See my "taps" aren't taps. The sink is a straight through spout with just a toggle off/on switch beside it and the shower is a straight hose to a camping shower head, again not a tap and with an off on switch. So full control must come electrically.

Hence the posts about diodes etc to prevent the other line running water when you want the firs tone only.

So never mind now, easy solution to buy a second pump.

Regards to all
AnswerID: 593894

Follow Up By: pop2jocem - Thursday, Dec 17, 2015 at 13:20

Thursday, Dec 17, 2015 at 13:20
OK I understand now. What you are intending is just an alternative to 1 pressure pump.

The only thing you might want to check on is if the pumps you are going to use have some sort of delivery and suction valves. If not you may need to install non return valves in the 2 top "Y" suction lines or the pump which has been selected will try to draw air through the other "Y" leg and cavitate because there is no tap to block it off.

Cheers
Pop
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Reply By: eaglefree - Thursday, Dec 17, 2015 at 15:37

Thursday, Dec 17, 2015 at 15:37
Yes Pop. think you have it.

This was the original purchase. Last night I purchased a second pump alone for $29.90. They say they have a "check valve". I imagine that means a built in one way valve so should be ok.

Really love this sight to sort out problems. Am in a regional area in Strathbogie tablelands Victoria.

Tony
AnswerID: 593899

Reply By: swampy - Thursday, Dec 17, 2015 at 16:02

Thursday, Dec 17, 2015 at 16:02
hi,
A form of flow control will need to be inline on the output side of pump .
The pump needs to pulsate to some degree if not it will not keep up with the demand.
If it barely pulsates u need to consider a larger pump.
A pump with internal bypass circuit is also a benefit ,reduces the aggresion of pump pulsation .

To simplify the system ,as been said before fitting taps at the sink & shower would have been the preferred method ..
In line ball valve would be ideal on the cheap / tap with wall mount fitting for the shower

A large cheap pump is around 75 17ltr flow and a large brand name is around 100$ 11 ltr flow

swampy
AnswerID: 593900

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