Testing water pump no power.

Submitted: Sunday, Nov 02, 2014 at 11:54

ThreadID: 110018 Views:2506 Replies:3 FollowUps:10

This Thread has been Archived

jat g

Since adding a shunt my water pump stopped working. It seemed to be ok for 2 days the readings were fine now after I turned it on it seemed to have little to no power then it died altogether.

I began by testing continuity from battery. But now am boggled why at only some moments I am getting a reading on both neg and pos wire whilst on one end am only on possive.

Both Positive and negitive have been disconected from the terminals. I am testing with a multi meter on oms.

Back Expand Un-Read 0 Moderator Share

Reply By: Allan B (Member, SunCoast) - Sunday, Nov 02, 2014 at 13:11

Sunday, Nov 02, 2014 at 13:11

Forget testing continuity with a multimeter. It is likely to provide unrealistic readings which will confuse you. Trust me.

Your best method of testing is to reconnect to the battery and switch the pump on. Then use your meter on 'Volts' to test for 12v at the pump terminals. If you do not get 12v at the pump terminals proceed as follows: With the multimeter on 'Volts', connect its negative probe to the battery negative post and use the meter's positive probe to observe voltages starting from the battery positive post then along the positive wire, where accessible, all the way to the pump. The meter should be reading close to +12v all the way. If not then the fault is between the last +12v reading and the next low reading.

If you are reading +12v all the way to the pump, then test the negative wire from the battery as before still with the meter's negative probe on the negative battery post. Use the meter's positive probe to test from the negative side of the pump back along the negative wire to the battery. The meter should be reading close to zero volts all the way. At any point where the reading changes significantly from the last reading is the failed connection.

Do not be tempted to connect the meter's negative probe to a reference point anywhere but the actual battery negative post, right on the lead post, not the clamp terminal, or you could get false readings. Also do not have the engine running or any other loads such as radio switched on.

Cheers
Allan

Member
My Profile My Blog Send Message

AnswerID: 541213

Follow Up By: Allan B (Member, SunCoast) - Sunday, Nov 02, 2014 at 13:45

Sunday, Nov 02, 2014 at 13:45

Further to the above, and as a general rule for circuit testing, a voltmeter can provide unrealistic readings due to its high impedance. The circuit under test could have a point of high resistance yet the voltmeter may read the full source voltage.

A better test device can be using a 'test lamp' made by using a 12v auto lamp, say a 6 watt tail lamp, connected to a pair of test probes, or even just the bare ends preferably soldered to prevent fraying.

This test lamp provides a load of about 0.5 amps which provides some assurance that the circuit is able to deliver current.
The lamp can be protected by a small clear plastic bottle or similar.
It is also wise to check the lamp before troubleshooting by connecting to a known 12v source.

A more robust test lamp can be constructed by using a 22 ohm 5w resistor in place of the lamp with a pair of LED's to indicate voltage. Connect the LED's back to back (cathode to cathode) with a 1k resistor in series, across the 22 ohm resistor. Back-to-back LED's will then indicate without concern as to polarity.

Cheers
Allan

Member
My Profile My Blog Send Message

FollowupID: 827249

Follow Up By: jat g - Monday, Nov 03, 2014 at 07:22

Monday, Nov 03, 2014 at 07:22

Just as you say, it was confusing and giving faulse readings.
But we ended up doing the Volt test as you decribed. All seemed fine.
I like the idea of rigging up a test lamp. Wiil do that.

I tested the pump directly to a spare battery I had, guess what, it worked.

Now I heard about the GROUND being often the main reason so I cleaned that up.
Then the SWITCH, I jumped it. Still no success.

Joined the a wire from switch to pump nothing.
Took a wire from ground to negitive terminal of orriginal battery where it was connected - YES works.
So posivite side ok.
Ground not, why not? Mmmm it was working - Here's the answer I had disconected a Navra relay which had a neg ground to chassis. So now with no negivite ground connected no power to pump. I didn't relise this any quicker because there was a negative connected at the terminal along with the positive. That neg was however for conection to the hot water system ignition nothing to do with the pump. Which I took me the whole day before I'd realised how the whole thing was wired.
Man oh man how frustrating it is, with a memory like a siv sure didn't help.

So today I will make up a new lead to ground the aux battery to chassis.

Many thanks for your help, it will come also in very handy for future events.

FollowupID: 827296

Follow Up By: jat g - Monday, Nov 03, 2014 at 07:26

Monday, Nov 03, 2014 at 07:26

I take it that the little power it had before dieing was left over energy in the wires. Otherwise?!?

FollowupID: 827298

Follow Up By: Allan B (Member, SunCoast) - Monday, Nov 03, 2014 at 08:11

Monday, Nov 03, 2014 at 08:11

Good result.

Cheers
Allan

Member
My Profile My Blog Send Message

FollowupID: 827300

Follow Up By: Member - Bruce C (NSW) - Monday, Nov 03, 2014 at 09:10

Monday, Nov 03, 2014 at 09:10

Hi Allan,
Is this what you were suggesting for the test lamp

Test Lamp circuit

Cheers, Bruce.

At home and at ease on a track that I know not and
restless and lost on a track that I know. HL.

Lifetime Member
My Profile Send Message

FollowupID: 827301

Follow Up By: Member - Bruce C (NSW) - Monday, Nov 03, 2014 at 09:15

Monday, Nov 03, 2014 at 09:15

Sorry Allan, I forgot to change the format from BMP to JPG.

Is this what you were suggesting.

12 Volt Test lamp circuit

Cheers, Bruce.

Perhaps the mods could remove the previous followup. Thanks, BC.

At home and at ease on a track that I know not and
restless and lost on a track that I know. HL.

Lifetime Member
My Profile Send Message

FollowupID: 827302

Follow Up By: Allan B (Member, SunCoast) - Monday, Nov 03, 2014 at 10:07

Monday, Nov 03, 2014 at 10:07

Yes thanks Bruce, exactly that. I think I'll get you to draw all my schematics from now on. lol

Just to add, the 1k resistor in series with the diodes can be anything from 680 ohms to 1k ohms, 1/2 watt, just to limit the current to LED limits.
The 22 ohm load resistor must be 5 watt wirewound to handle the load current. (Jaycar RR-3258) And it will get warm if left on too long.

For those unaware, the LED anode (A) is the longer leg.

Cheers
Allan

Member
My Profile My Blog Send Message

FollowupID: 827305

Reply By: Allan B (Member, SunCoast) - Monday, Nov 03, 2014 at 10:32

Monday, Nov 03, 2014 at 10:32

.

WARNING

After Bruce posted the schematic for an LED test lamp with a load resistor I thought to add links to ready-made test lamps.
What I did find however were warnings about the possibility of setting off airbags whilst probing around with test lamps containing incandescent lamps or load resistors.

My old Troopy does not have airbags but if you do have them, better be careful of where you are probing, or use only low-current test instruments such as a multimeter or LED test lamp without a load resistor.

In general, I can see risks associated with working on the vehicle electrics when airbags are fitted. Setting them off can be a very expensive error and possibly render the vehicle undriveable!

Cheers
Allan

Member
My Profile My Blog Send Message

AnswerID: 541248

Follow Up By: Member - Bruce C (NSW) - Monday, Nov 03, 2014 at 12:12

Monday, Nov 03, 2014 at 12:12

Thanks for the heads up Allan.

I may have gotten a terribly serious surprise me thinks. Not to mention being totally fizzed off with myself as those replacement airbags don't come cheap.

At home and at ease on a track that I know not and
restless and lost on a track that I know. HL.

Lifetime Member
My Profile Send Message

FollowupID: 827308

Reply By: Allan B (Member, SunCoast) - Monday, Nov 03, 2014 at 12:12

Monday, Nov 03, 2014 at 12:12

For those who would wish to purchase a LED 12v circuit tester this one from Supercheap or similar from other auto accessory stores would do.

LED Circuit Tester

Cheers
Allan

Member
My Profile My Blog Send Message

AnswerID: 541251

Follow Up By: jat g - Tuesday, Nov 04, 2014 at 06:29

Tuesday, Nov 04, 2014 at 06:29

Dad digged up one of those yesterday whilst rumaging. Looks like I'II be needing it today. 12V connection from fridge not working. Can't believe it, here we go again.
240V via transfomer works ok though which means its not the fridge. Thinking switch ATM, as I have changed the fuse. 12V is connected to load terminal of solar panel regulator - checked connections all AOK.
Not only that but I read last night that the Regulator gave a reading of max voltage 16V ...... thats not right, max is suppossed to be 14.2V program 3 sealed gel for Dingo 40/40. What the heck now.

I feel a nervous brake down coming on.

FollowupID: 827350