RC Electric Off-Road Trucks, Buggies, Truggies and more Discuss electric RC off-road, buggies & trucks here. Also discuss brushless motors, speed controllers aka ESC's, brushed motors, etc

Using a multimeter

Old 12-12-2004, 12:51 PM
Senior Member
Thread Starter
Join Date: Oct 2004
Location: Stockton, UNITED KINGDOM
Posts: 189
Likes: 0
Received 0 Likes on 0 Posts
Default Using a multimeter

I was looking at discharging a battery pack with a bulb discharger and a multimeter to measure voltage drop, could I do this and turn of the discharge when it reaches 5.4v or is it harder than that?
Old 12-12-2004, 03:13 PM
Join Date: Dec 2004
Location: Brooklyn, NY
Posts: 70
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Using a multimeter

If you simply put the meter across the battery and watch it….sure, no problem.

I haven’t actually built this, but if you know how to solder and feel adventurous you can build a little circuit that will cut of the battery at 5.4v

All you need is 2 Schottky diodes and a 5VDC relay. The schottky diodes don’t have to be RC quality….cheap ones will do. The relay can be something like this...

In the US we would buy this stuff from RadioShack. If you don’t know of an electronics supply place then ask the local hobby shop...they should know.

How it works:

When you connect your battery to the discharger, you will power the relay coil and the relay will turn on, connecting your battery to the bulb. When the battery voltage drops just below 5.4 volts, the relay will turn off, cutting of the bulb.

Why it works:
The coil on the relay needs at least 5 volts to work. Schottky diodes require 0.2 volts in order to conduct electricity. So, 5 + 0.2 + 0.2 = 5.4 volts needed to operate the coil.

How to build it:
What you want is to create two very simple circuits. First circuit is the one you already have, except that you’re going to cut one of the wires and connected it to the CONTACTS of the relay. Basically, you just added an on-off switch to your circuit.

The next circuit to build is completely new, but almost as simply. You want to power the coil of the relay with the battery you’re discharging. The best way is to solder two wires to the (+) and (-) of the discharger, and run them to the COIL of the relay. Cut the (-) wire, and add the two diodes in series.

Here's a rough diagram...

--discharger(-)------relay CONTACT----(-)battery (+)

--discharger (-)----(S)diode----(S)diode---relay COIL

The discharger (+) and (-) are the SAME POINTS in both circuits. I just show it as two circuits so you can see the difference.
The (S) on the diodes is the stripe. You just splice in the diodes in series in the (-) wire.

If you put the diodes in backwards, the coil just won’t turn on. No harm done. Just reverse them. In fact, it’s really difficult to damage anything with this circuit.

To make the COIL circuit a little simpler, use one regular diode instead of two Schottky diodes. The COIL will turn off when voltage drops below 5.7 volts.

Good luck!

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.