thank you all for the info
i guess electronics is to reduce amps (in automotive electrics ) as over the years wires sizes have
got smaller ,
but they still have big batteries and starter motors to get the 10litre engines going, maybe why using a
big hammer to knock big nails in works .
Thanks again

 

misterbill2 could you please explain the parts used to make this ie you say (5ohm and 1 ohm ) what size type etc and if poss a drawing as not sure thanks graham

 

Sorry about no circuit drawing, I am not near the computer that has the drawing software. For the resistors I was thinking of the type in the gold-colored aluminum blocks, mounted to a piece of aluminum perhaps 1/8 or 1/4 inch thick. That same piece of aluminum can then have a hole to mount the NO pushbutton. The resistors can be the 5 watt size because current can only flow when the button is pushed. That portion of the circuit is a string, just like the drawing on the starting post. The connection goes from the battery plus to one side of the PB switch, then a connection from the other side to the 1 ohm resistor, then a connection from the other side of the 1 ohm resistor to a terminal of the five ohm resistor. From the other terminal of the five ohm resistor comes the positive connection to the wire to test. The Positive side of the green LED connects to the other button terminal from the battery connection, the negative side of the LED connects to the 74 ohm resistor, and the other end of that resistor connects to the wire between the one ohm and five ohm resistors. For the low current check part, the positive terminal of the yellow LED connects to the battery plus side of the button, the negative side of the yellow LED goes to one side of the 1200 ohm resistor, and the other side of the 1200 ohm resistor connects to same terminal of the five ohm resistor as the positive connection for the wire to test.. The negative connection part is exactly the same as your original circuit with the 3 light bulbs..
HOW IT WORKS:
When the checker is first connected the yellow LED should light if there is any continuity because it is drawing less than 20 milliamps. Pushing the button puts a 6 ohm load on the wire, drawing 4 amps, and 4 amps through the 1 ohm resistor provides 4 volts to the green LED with the 74 ohm resistor serving to limit the current. It can get away with using 20 watt resistors because current only flows when the button is pushed, so don't hold the button on for very long. 2 or 3 seconds should be enough to see that the wire is OK or not.

It should be simple to draw the circuit based on my description, I can see the circuit very clearly in my mind. Sort of like a road map.

 

For the tester use a 5 ohm and one ohm resistor in series, with a green LED and it's own 74 ohm resistor across the big one ohm resistor.
That is for the 4 amp check. Then for the low current tracing check, just a yellow LED with a 1200 ohm resistor to give a low current check. Add a NO pushbutton in series with the high current side to avoid a big heat build up.But it does not have the red LED to show open. That is why the yellow one is included.

I believe what Mr. Bill has in mind would look a little like the following:

R1 and R2 total about 6 Ohms so in a 24 volt circuit 24 / 6 = 4 Amps. The actual values of R3 and R4 will depend on the actual LEDs used. This is why D1 & D2 do not have labeled part numbers. V1 24 Volts merely represents the 24 VDC system power and I omitted the normally open push button switch. I believe this is approximately what the circuit would look like. Mr, Bill or anyone else feel free to correct what I have here. A 20 Watt resistor should be OK for R1 but R2 should be about a 100 Watt (big resistor).

I see Mr Bill replied and even for momentary push button use I did go with a much higher resistor wattage. I would use, as suggested, the aluminum housing resistors.

Ron

 

And note that the push button switch has to be able to switch 4A.

 

Here's my take on Mr. Bill's verbiage: (and I swapped the 1Ω & 5Ω resistors because the numbers didn't work out the other way) (and 3vf means 3 forward volts, the voltage drop across some LED's. As Ron said, the actual voltage will vary with the LED you choose. Numbers will change)

[edit] Sorry, no buzzer.

[edit] Drawing removed due to error.

 

(and I swapped the 1Ω & 5Ω resistors because the numbers didn't work out the other way)

But the green LED and 74Ω resistor must be connected across the 1Ω resistor.

 

But the green LED and 74Ω resistor must be connected across the 1Ω resistor.

I missed that. I tried to go as much as possible according to the verbal description of how it was wired and that's what I came up with, but I swapped the 1 and 5 ohm resistors because the description said one side of the green LED was connected to the switch. The way I have it drawn it drops 20 volts across the 5 ohm resistor. If I've got it wrong - let me know exactly how to change my drawing and I'll make the changes.

 

I missed that. I tried to go as much as possible according to the verbal description of how it was wired and that's what I came up with, but I swapped the 1 and 5 ohm resistors because the description said one side of the green LED was connected to the switch. The way I have it drawn it drops 20 volts across the 5 ohm resistor. If I've got it wrong - let me know exactly how to change my drawing and I'll make the changes.

When the button is pressed there would be 20V across the 5Ω resistor and 4V across the 1Ω resistor. As drawn, the calculation for the green LED current would be 20V - 3vf = 17V, 17V / 74Ω = 230mA and most LEDs won't stand that for long.
Either:
1. Swap the resistor values.
2. Change the 74Ω to 1.2k
3. Move the green LED and its resistor so it is connected across the 1Ω resistor.

 

1. Swap the resistor values.

Corrected. Thanks Al.

 

Corrected. Thanks Al.

View attachment 150206

Yep, that'll do the job.

 

WOW thanks very much all of you ,
just looking at parts needed will these be ok

10mm LED Diffused 200mcd 40°
https://www.ebay.co.uk/itm/10-x-Amber-10mm-LED-Diffused-200mcd-40-/252431180635?hash=item3ac612235b

Green 10mm LED Diffused 300mcd 50°

75 Ohm 0.25W Metal Film Resistor
1.2K Ohm 0.25w Carbon Resistors 1/4w Resistor

Resistor, Axial Leaded, 5 ohm, HS Series, 25 W, ± 5%, Solder Lug, 550 V

Resistor, Solder Lug, 1 ohm, HS Series, 100 W, ± 5%, Solder Lug

and once again thanks very much

 

Resistor, Axial Leaded, 5 ohm, HS Series, 25 W, ± 5%, Solder Lug, 550 V
Resistor, Solder Lug, 1 ohm, HS Series, 100 W, ± 5%, Solder Lug

The 5Ω should be 100W and the 1Ω should be 25W

 

ok thanks will swop around , are the other ok

 

ok thanks will swop around , are the other ok

Yes, looks good to me.

 

Corrected. Thanks Al.

View attachment 150206

THANKS TONY!!! Your drawing is exactly what I was saying. Perfect. And yes, I should have mentioned that the push button switch should be good for at least 4 amps. It might be that some experimenting will be needed, depending on the forward voltage of the LED devices used, but most of the red ones switch on around 1 volt, so that is why 74 ohms. Also, I think that is a standard 10% tolerance value.

 

@MisterBill2 Last year I bought a bunch of LED's. Super Bright. I tested ten of each color and charted their forward voltages.

3 mm Clear Blue: 2.82 Vf avg; 2.8 min; 2.83 max; 0.01 v standard deviation (STD)
5 mm Clear Green: 2.92 avg; 2.72 min; 3.03 max; 0.11 v STD
5 mm Clear Red: 1.95 avg; 1.92 min; 1.95 max; 0.01 v STD
5 mm Clear Yellow: 2.01 avg; 1.98 min; 2.07 max; 0.003 STD
5 mm Clear White: 2.97 avg; 2.92 min; 3.01 max; 0.003 STD

5 mm RGB LED: Red 2.1, Green 2.8, Blue 2.9 forward volts

This list is to demonstrate that no matter what you expect for a value, it CAN be anything. But these numbers seem to be close. Using the values I listed SHOULD get you pretty close to 15 milliamps. Which should be plenty bright to see in daylight.

Whatever voltage you're starting with you subtract the forward voltage of the LED from that. Then you calculate for the current you want to use. It's typical to see LED's run at 10 mA, and that should be plenty bright. 20 mA is considered typical max for LED's. 15 mA is a good in-between for daylight observation. I don't know how well this would fare in full direct sunlight, but I'm thinking you should be able to see them with just a little bit of shade. Experimentation is in order.

 

@MisterBill2 Last year I bought a bunch of LED's. Super Bright. I tested ten of each color and charted their forward voltages.

3 mm Clear Blue: 2.82 Vf avg; 2.8 min; 2.83 max; 0.01 v standard deviation (STD)
5 mm Clear Green: 2.92 avg; 2.72 min; 3.03 max; 0.11 v STD
5 mm Clear Red: 1.95 avg; 1.92 min; 1.95 max; 0.01 v STD
5 mm Clear Yellow: 2.01 avg; 1.98 min; 2.07 max; 0.003 STD
5 mm Clear White: 2.97 avg; 2.92 min; 3.01 max; 0.003 STD

5 mm RGB LED: Red 2.1, Green 2.8, Blue 2.9 forward volts

This list is to demonstrate that no matter what you expect for a value, it CAN be anything. But these numbers seem to be close. Using the values I listed SHOULD get you pretty close to 15 milliamps. Which should be plenty bright to see in daylight.

Whatever voltage you're starting with you subtract the forward voltage of the LED from that. Then you calculate for the current you want to use. It's typical to see LED's run at 10 mA, and that should be plenty bright. 20 mA is considered typical max for LED's. 15 mA is a good in-between for daylight observation. I don't know how well this would fare in full direct sunlight, but I'm thinking you should be able to see them with just a little bit of shade. Experimentation is in order.

Yes! Just exactly what Tony said. And I was right about the red ones being just a bit less than 2 volts.;

 

How about this circuit 4A test current:

It is principle only.
If you agree with it, we can add more LEDs, buzzer etc.
Edit: We can decrease dissipating power of R3 up to 6W, using module $5.98:
https://www.ebay.com/itm/5A-Digital-Control-DC-DC-Step-down-Power-Buck-Module-5-36V-to-1-32V-12v-5v-24v/152228350713?_trkparms=aid=444000&algo=SOI.DEFAULT&ao=1&asc=50998&meid=fc8f12c7ca354915bb156c4c6193eef6&pid=100752&rk=5&rkt=6&sd=152332717605&itm=152228350713&_trksid=p2047675.c100752.m1982

Even more: we can put new resistor R4 about 40 Ohm, in series with D1, then we will see tested wire state on display (Input voltage of converter).
Lower voltage - lower resistance of wire.

 

ok so today i made ' the tester ' it works perfectly
so a BIG THANK YOU to all who helped me ,

next mission to make one that works at 5v and say about 2amps
to check the sensor wiring from ecu's

poss 4.5 v battery