4QD - DC Motor Control

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Battery Condition Meters

The circuit uses LEDs (Light Emitting Last) to give a 'line of light' type display which extinguishes from the top as the battery is discharged. In most applications it is connected to the battery via an ignition switch so that it extinguishes when the machine is turned off. It is currently available in three standard versions:

5 LED and 7 LED can be made for 36v operation, subject to minimum quantity order. The differences between 24v and 36v versions are minor as are the differences 48v and 36v so modification is simple.

The seven LED board could be made for 60v operation. Other versions with more LEDs could be produced to order, subject to minimum quantities. Other voltages and shapes can be designed to order.

By using LEDs the boards can tell you more about the battery than a simple moving coil meter will: this is because the LEDs do not suddenly switch on and off, but each LED fades over a range of voltage. The voltages are also a lot more accurate than cheap moving coil meters.

The circuitry is very versatile and can be adapted for anywhere a 'line of light' type voltmeter is required. 4QD can economically customise it for quite small quantities.


The LEDs extinguish at approximately the following voltages (other specifications to order):-

7 LED (48v) 5 LED (24v) 3 LED (12v)
LED 1 49.7 - 49.2     Green
LED 2 47.9 - 47.4     Green
LED 3 46.1 - 45.6 25.1-24.6 12.3 - 11.8 Green
LED 4 44.3 - 43.8 23.3-22.8   Green
LED 5 42.5 - 42.0 21.5-21.0 10.3 - 9.8 Yellow
LED 6 40.7 - 40.2 19.7-19.2   Red
LED 7 38.9 - 38.4 17.9-17.4 9.0 - 8.5 Red

Note that the yellow LED goes out at about 10.5v (21v or 2 x 10.5v for the 24v versions, 31.5 for 36v and so in). This is about the lowest voltage you should discharge to: over-discharging a battery can permanently damage it. The 'span' on the 5 LED meter is about 8 volts - which is OK for 24v operation and for 36v. Span on the 7 LED board is about 10v.

Sizes of the boards are:

The boards mount behind a panel, with a rectangular slot for the LEDs and two fixing holes at the end of the slot. Full details are in the instruction manual.

Ordering information and prices.

Click on the link to the price list and the secure shopping cart.
ItemPrice ListAdd to cart
3 LED meter for 12v:BCM-312Add
5 LED meter for 24v:BCM-524Add
7 LED meter for 48v:BCM-748Add


You can download the instruction manual from our manuals and catalogues page.

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© 1997-2015 4QD/4QD Ltd.
Page's Author: Richard Torrens
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Last modified: 2015