ohms reading confusion

[kevtherev]

I have been checking my manifold heater resistance.
Spec asks for 0.25 to 0.50 ohms
I checked the reading with my multimeter which has ohms scale .. 200, 2k, 20k, 200k, 2m, 20m.
I used the lower of the options (200) and got a reading of 2.5.

Am I right in assuming the meter itself will not go low enough to gain the correct reading?

and.. would a grounded element show a resistance of zero (infinite)

[VWCamperfan]

2.5 should be 2.5 ohms on your meter with that setting.
Try just putting the probes together and see what reading you have. The final reading can vary quite a bit depending on what leads you use.
It should read 0 (zero) but if it doesnt, just subtract that number from your meters ohm reading when testing something.

[1664]

2.5 should be 2.5 ohms on your meter with that setting.
Try just putting the probes together and see what reading you have. The final reading can vary quite a bit depending on what leads you use.
It should read 0 (zero) but if it doesnt, just subtract that number from your meters ohm reading when testing something.

He's trying to measure 0.25 not 2.5 though. With the probes together you should be able to 'zero' the meter by turning the little screw in the bottom centre of the view glass with a slotted screwdriver.

I assume those last two are 2M and 20M in which case 200 is the lowest and the chances of an accurate reading of between a quarter and a half an ohm on that scale is wishful thinking.
a grounded element would be nigh on 0 ohm on the lowest setting.

I've got a good old fashioned AVO meter here Kev if you'd like me to bring it to Vanfest

What the hell's a manifold heater anyway.........

[1664]

err......I'm assuming you're using a cheapo analogue multimeter from the pound shop aswell

[kevtherev]

Thanks mate
so if the meter went down further to 20 and I tested the circuit then would it would read 0.25?

Ok I checked the meter itself by touching the probes and it shows 0.3 ohms on the 200 setting.
I don't have an adjustment screw Bren...and, Yes I would like you to bring it to VF please.

i'm using a Clarke CDM20 with a digital display.. I get by

[VWCamperfan]

He's trying to measure 0.25 not 2.5 though.

Yes but the reading he's getting is 2.5, which is why I wanted him to check the resistance with the probes connected together.

[toomanytoys]

As said.. never see a .25 ohm reading on a 200 ohm scale... unless you have a very expensive "Fluke" (or similar) meter.....

[1664]

The closer the range is to the value you're trying to measure the more accurate it should be. Having said that a digital should be better than an analogue. Maybe the resistance IS 2.5 ohm (less 0.3 = 2.2 with probes)

[VWCamperfan]

so if the meter went down further to 20 and I tested the circuit then would it would read 0.25?

No it wouldnt kev, at it's lowest range the meter will display what the resistance actually is.

0.25 ohms seems extrememy low though, that would be drawing 48 amps!

[toomanytoys]

so if the meter went down further to 20 and I tested the circuit then would it would read 0.25?

No it wouldnt kev, at it's lowest range the meter will display what the resistance actually is.

0.25 ohms seems extrememy low though, that would be drawing 48 amps!

Yeah I was thinking.. that would be a shed load of current... cant be right surely...... the heater would be glowing.........

[kevtherev]

so if the meter went down further to 20 and I tested the circuit then would it would read 0.25?

No it wouldnt kev, at it's lowest range the meter will display what the resistance actually is.

0.25 ohms seems extrememy low though, that would be drawing 48 amps!

ok.. well these are haynes values and the highest is 0.50 ohms.
maybe someone else can check their manifold heater element resistance?
simply disconnect the thick red wire that disappears under the manifold connect the probe to the red wire spade and the other to the inlet manifold...and read. (not injection)

[1664]

I didn't bother to think of the current - so this manifold heater thingy is hooked directly to the vehicle 12v supply; no electronics in between or anything?

Just checked my AVO ranges too and it might just manage to register the value

[kevtherev]

OK quick description...
the heater has a relay in the junction box it has direct current from the battery.
the relay is triggered by the sensor on the thermostat housing (lilac and black).
when temp reaches 60 deg C the thermoswitch separates and the relay switches off.

All this is for a smoother warm up transition as fuel hits the cold manifold and freezes.. sort of a de icer.

[toomanytoys]

Start on gas Kev... never need it then.....

[kevtherev]

Start on gas Kev... never need it then.....

it does help Si I've tried both heater on and off (I have a manual switch for the relay ....long story)
During warm up with heater on it seems to tick over nicley, without it the engine seems lumpy.