Need to safely run a 100 volt voltage gauge leads. Use a resistor?

Thread Starter

eddie500

Joined Nov 5, 2011
43
I need to run from the back of my car to the front a 100 volt wire from the hybrid battery. The wire is for a 100 volt volt gauge.

My question is since I don't want to have 100 volt wires run to the front of the car for safety. Can I simply just use a 100K ohm resistor at the start of the wire run that will limit the current to very low levels without changing the voltage reading?

I assume because a volt gauge draws so little current, the voltage will be very close (99%+) to the real voltage and this will limit the current in case of a short or touching the wire and killing someone.

Please let me know what you guys think and what resistor value I should use or if I should do it another way.

Here is a link to the voltage gauge I will use and have mounted at the front of my car.
https://www.aliexpress.com/item/GWUNW-BY536V-DC-0-99-999V-100V-Voltage-Tester-Meter-digital-voltmeter-5-bit-high-precision/32841613186.html?spm=a2g0s.9042311.0.0.4f354c4d5Li5wj
 

crutschow

Joined Mar 14, 2008
23,361
That meter has an input impedance of 1 Megohm, so using a 100k ohm resistor in series will reduce the voltage about 10%.
To limit the current to a safe value in case of shock or short circuit, use a 10kΩ, 2W resistor in series (it will dissipate about 1W under short conditions.
That will reduce the voltage to the meter by only about 1%.
 

MisterBill2

Joined Jan 23, 2018
3,883
Crutschow advice is fine, I would use a 1000 ohm quarter watt resistor, which would limit any short circuit current to 12 mA, and it would burn out after a short time. Resistors are cheaper than fuses and if a short happens once then work needs to be done to fix it. And if one side of the battery is grounded then that lead to the meter probably does not need protection. Just don't have the resistor embedded in the wiring.
 

ericgibbs

Joined Jan 29, 2010
8,739
hi eddie,
When you say, for 'safety' are you referring to your personal safety from a lethal electrical shock.?
Using a low value resistor will not give you that level of safety.

100v/1000R =100mA

E
 

crutschow

Joined Mar 14, 2008
23,361
I would use a 1000 ohm quarter watt resistor, which would limit any short circuit current to 12 mA
Your calculator needs batteries. ;)
Or were you thinking it was a 12V battery?

10kΩ will limit the current to 10mA, which should be safe for electrical shock.
 
Last edited:

spinnaker

Joined Oct 29, 2009
7,815
The meter is only going to draw whatever it draws which is probably next to nothing. To prevent short (i.e. fire) the wire should be fused with a low value fuse. You could add the current limiting resistor as an added safety feature to prevent possible shock.
 

MisterBill2

Joined Jan 23, 2018
3,883
Your calculator needs batteries. ;)
Or were you thinking it was a 12V battery?

10kΩ will limit the current to 10mA, which should be safe for electrical shock.
Yes, my mistake. Indeed I was thinking of a 12 volt battery. 10Kohms is a better choice for the higher voltage. Sorry about forgetting that it was a higher voltage battery pack. Probably 8 of the 12mvolt cells in series.
 

crutschow

Joined Mar 14, 2008
23,361
To prevent short (i.e. fire) the wire should be fused with a low value fuse. You could add the current limiting resistor as an added safety feature to prevent possible shock.
If you have an adequately power rated resistor at the battery end, you don't need a fuse.
 
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