DIY Vantec modification


This page describes a particular behaviour of certain Vantec speed controllers and one way to change that behaviour. Note that no guarantee is given for this procedure. You should not attempt to modify any speed controller unless you are thoroughly competent with soldering small electronic components. If you have to return your Vantec to the manufacturer, and this modification is present, you will probably be charged for rectification work. This modification has been performed on several Vantecs (more than one model) and so far has worked fine, but it is not condoned by Vantec and there is no guarantee that it will work on yours, or will not change some other property of the controller. You're on your own!

If you are not experiencing the behaviour described below, it is recommended that you do not make any changes to your controller. If it isn't broken...


It has been noticed by several people that when certain Vantecs (it has been observed on several different models of Vantecs) are used in certain situations, there is the possibility of the Vantec resetting itself under high-load conditions. Alan Gribble, creator of the great Pussycat, observed this behaviour on one of his Vantecs a couple of years ago and set about finding a 'fix'. After some considerable research, he developed the procedure described below. Many thanks to Alan for allowing the procedure to be publicised.

We observed it when running our RDFR47E at 36 Volts (three sets of 3Ah NiCads) driving a pair of Bosch GPA 750 motors. In retrospect, it was also what caused KHz mobility problems in BattleBots Season 4 against Little Sister and Surgeon General. Whenever a full power start was attempted, the Vantec would reset, which would cause the motors to loose all power for about one second. After the one second, the controller would recover fully.

If driven around 'softly', there would be no problem. The behaviour was also noticed when running at 24 Volts, but less so. Once the 24V batteries had been discharged to around half capacity, the controller usually behaved fine, so it seems to be related to the amount of load that the controller is having to handle - light loads and everything is OK (you will not be able to reproduce it with the machines wheels in the air), but over a certain limit, the behaviour starts appearing.

We attempted other solutions, like fitting a large capacitor to the input lines on the Vantec and several ferrite sleeves to the motor leads, but with no noticeable effect.

factory.jpg (61448 bytes)There was thought to be a factory 'fix' for this behaviour. On Vantecs purchased since the middle of 2001, maybe earlier, it has been noticed that a capacitor and diode had been added to the circuit board, highlighted on the picture on the left. Click on the picture for a larger view. However although our Vantec RDFR47E, purchased in late 2001, had this 'fix', it still exhibited the behaviour.

Altering the behaviour

The procedure involves soldering two new components onto the control board of the Vantec. The controller should not need to be disassembled.

The components are:
60 Volt, 5 µF electrolytic capacitor e.g. RS partno 324-5335
10 K Ohm resistor

It is also recommended that you attach an AC Varistor/Transient Voltage Suppressor across each of your motors. e.g. RS partno 354-5180, manufacturers partno P6KE47CA. This cuts down on voltage spikes generated by the motors getting into the controller.

layout.jpg (115073 bytes)The positive end of the cap and one end of the resistor are both soldered onto pin one of the 14 pin DIL chip on the right of the picture. The negative end of the cap is soldered into an unused solder pad on the board and the other end of the resistor is soldered onto a nearby track.

varnish.jpg (101672 bytes)To solder the resistor to the track, take a sharp knife and carefully scrape off the green varnish, exposing a few mm of bare track. The exposed track, and the solder pad for the cap are circled in the picture. Be very careful not to damage the track itself. You may need to use a magnifying glass - those tracks are small!

resistor.JPG (36600 bytes)You can now solder the resistor in place. One end is soldered onto pin one of the chip, although in this case, the controller had the factory 'fix', so it was easier to solder onto the leg on the diode that is also attached to pin one.

final.JPG (131084 bytes)The capacitor can now be soldered in place. The negative wire should be passed through the solder pad hole. Be careful to crop the wire before soldering so that it does not protrude too far from the other side of the board. It may not go all the way through the hole - ours was blocked by glue on the other side. The positive wire is also attached to pin one of the chip.

Once you are happy all is secure, put a blob of contact adhesive or cyano on the components to keep them in place. Done! That's all you have to do. Go and test it and keep your fingers crossed.