correct ohms reading for gt380 coils

[Ramjam]

hi
Can anyone advice me on how to go about checking the resistance on my old coils? Primary and secondary circuits?
thanks
Mj in Beirut

[tz375]

Low tension side, disconnect coils at the large 6 contact plug and test between each pair of leads, Orange - White, Orange to B/W and Or-B.

For the HT leads (secondary) it's lead or cap top either of the low tension (primary connectors).

Primary is around 4-5 ohms and secondary is 12-15K IIRC.

[Ramjam]

and primary is tested with battery disconnected? And secondary with one lead of the voltmeter on the positive terminal of the coil and the second connected to the HT lead (with batt connected)??

thanks for your patience

M

[tz375]

Almost, but not exactly. Resistance is measured in Ohms and to measure that we disconnect power to the part and set the multimeter to ohms. The meter has an internal battery and it passes a certain amount of power through the item to measure the resistance to flow. It knows the voltage it's applying and measures the current and displays the answer as ohms.

If the part being measured is connected to any other wires or components we run the risk of a false reading.

[Ramjam]

i know all that. But are my connection suggestions correct?
thanks again

[tz375]

OK, let's try that again. Your last reply is somewhat inconsistent with the question.

The battery is disconnected - or at least the part you are checking is disconnected from the battery for any OHM checking.

[jabcb]

Since you are not 100% sure of what you are doing, its a good idea to disconnect the battery before you check any resistance.
Better save than sorry -- the battery might give you a false reading but worse yet it might damage your multimeter.

From your other topic, it looks like you have at least two different kinds of plug caps.
The right cylinder might have a non-resistor cap, while the center cylinder might have a resistor cap.

If you measure the secondary resistance with the plug caps installed, then you are measuring the combined resistance of the coil secondary + plug cap.

In order to make sense of the readings, you should remove the plug caps and take separate resistance readings of the coil secondaries & plug caps.

[Ramjam]

Please see attached photo to determine which type of coils i have. And here are my readings

Primary (multimeter set to 2000k) i got a reading of 004 for each of them

Secondary (multimeter set to 20,000) I got a reading of 9.03, 8.60 and 9.05

Caps were 2.83 and 3.50 (set at 2000 i think)

Please tell me if you think my coils are ok.
I am planning on changing the caps and leads in the next week when parts arrive btw

many thanks

[jabcb]

Looks like stock coils.

What multimeter do you have? Also, could you post a pic of the multimeter.
This will make it easier to figure out your readings.

Using the same scale you used for the secondary (9.03, 8.6 & 9.05 readings),
measure between the HT leads & the aluminum-colored metal bracket that attaches the coils to the bike.
Make sure to scrape around a little on the bracket so that you have a good electrical contact.

Using the same scale you used for the secondary (9.03, 8.6 & 9.05 readings),
what reading do you get when the multimeter probes are not touching anything?
(This is the open-circuit reading.)

[Ramjam]

the open circuit is always 1

here's a pic of the meter itself (from the net)

[jabcb]

about your multimeter……………….
Your multimeter is not auto-ranging. So to get the most accurate reading you need to select the correct range.
So when you look at the ohm settings on your multimeter just think of it as a scale.
For best readings from 0 to 200 ohms, select 200 ohms.
For best readings from 200 to 2000 ohms, select 2000 ohms.
& so on.

about testing your coils……………...
For coil primary resistance, select 200 ohms because the reading should be around 4 ohms.
For coil secondary resistance, select 20,000 ohms (20k ohms) because the readings should be around 10k.
For plug caps also use 20k ohm scale.

Please check again using the correct multimeter settings.

about an additional coil test………….
You also should check the coil for grounds.
Select 200 ohms on the multimeter.
Check between a primary wire & the aluminum-colored metal bracket that attaches the coils to the bike.
Make sure to scrape around a little on the bracket so that you have a good electrical contact.
Do this for all 6 primary wires.
You should get the open circuit reading.

[Ramjam]

HI
After a bit of time, i finally got round to checking the coils, as per your instructions.

For primary I have about 5 ohms on all three of them

For secondary, they are all around 9k except for one, which is 8.7k

Please tell me if the 8.7k one is a bit weak. What does it mean? Is it on the way out?
thanks
mj

[jabcb]

You also need to check the coils for grounds.

[Ramjam]

by the way. on the inside conductive 'tube' of the coil itself - where the HT lead is shoved - how much of it is actually electrically conductive? Is it the whole length of the tube or just the end where there is perhaps a spike?
thanks again
Mj

[jabcb]

I'm not sure what you are asking.

The coil consists of metal bar with the primary & secondary wires wrapped around it.
The wires are insulated & do not make any electrical contact with the metal bar.