Let's Make Robots!

High Power Switch

Vendor's Description: 

DAGU products support site: https://sites.google.com/site/daguproducts/

This is the "High Power Switch" from DAGU. Originally designed for the "Wild Thumper" robot chassis's it is a very versatile switch that can be used with any robot that draws more than the 2-3A that most small switches can handle.

This switch will work with batteries from 6V to 24V with a maximum voltage of 32V so you can charge your 24V batteries without damaging the switch.

Without any heatsinking this switch will handle 10A easily. Mounted on a CPU heatsink with heat transfer compound and a cooling fan and this switch will handle up to 60A continuous!! The FET's are fully insullated to simplify mounting requirements.

To make the switch as robot friendly as possible we have now added a socket for an external manual switch. This allows another switch to be more conveniently mounted. Simply leave the onboard switch in the "off" position.

A digital input allows the switch to be controlled by a processor. Simply connect the grounds and apply a voltage of ate least 1V to the digital input to turn the switch on. This gives a robot the ability to turn itself off after recharging it's battery.




Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.

Hi Oddbot,

Question from an ignorant so please bear with me, trying to learn.  


From your initial description of switch you state that for applications drawing more than 10A we have the option to mount on heatsink.  I note the two black mounting pads on the switch next to "IN" and "OUT" happen to be same dimensions as WTC.  WTC is mounted on it's heatsink with pads.  


Can you clarify for me if switch would be mounted on a given heatsink using pads or you meant switch PCB directly on heatsink (with some method of fixing) using a thermal compound, as you note the FET's are fully insulated ?


I also just learned what FETs are thanks to the WIKI page etc.  Apparently heralded the semi-conductor age.



OddBot's picture

Your question is a bit confusing. The switch comes with mounting screws that allow it to be mounted on a flat surface as you can see in the photos.

If you are using the Wild Thumper chassis then it's aluminium chassis can be used as a heatsink. The holes in the switch PCB are intentionally spaced to suit the Wild Thumper chassis. If your using the switch in something else then just drill some mounting holes in a heatsink (or aluminium plate) and mount the switch to it.

Some heat transfer compound should be smeared betweewn the FETs and the heatsink surface. Alternatively use some zinc cream (thick white sunblock) which is also primarily made from zinc oxide.

Actually Bi-Junction Transistors (BJT's) came first and I think diodes came before that.

Thanks for the reply oddbot, much appreciated. Perhaps I was confused because Ive just realised from a google image search that what I described earlier as the "pads" are indeed the FETs, with the three pins from each?

I use mechanical 6 pin switches with plastic casing for switching my motors which work on 24V. Due to heavy load and sparks during switching, plastic casing eventually gets hot and melts to block switch movement. Speed controll or mcu interfacing was not a problem yet. Searching for a substitute, i'm planning to try a mosfet h bridge. What do you think? Is it good over the mechanical switch? It's for a manually controlled robo for robowar events.

Also be aware if you work with switches or relays that the contacts need to be rated for DC. AC switch ratings are not valid for DC. The reason is that AC has zero current flowing at times. This extinquishes the arc when the contacts are opening and reduces the wear on the contact. Since DC never has a zero crossing the contacts need to be much heavier to handle the arcing.


Thanks for the advice. I've checked it. They are for DC circuits. Amps is the problem.

OddBot's picture

Although they can be used instead of mechanical switches it is obvious from your explanation that you were not using a suitably rated mechanical switch to begin with. As it's for a robot war event I would stick with a mechanical switch for safety reasons.

First of all you need to determine what is the maximum current your robot is drawing. If you use a 1A switch for a 50A load then of course it is going to melt!

What is the stall current of your motors? What weapons are you using and what is their maximum current draw? You say your system is 24V so you really need a heavy duty switch for a truck or bus as they use 24V. If your hard up for money then go to a wreckers / junk yard otherwise I would buy a new switch for greater reliability.

Make sure your power wiring is also rated for the same maximum current otherwise during battle your robot will end up under-powered. If your max current is 30A then make sure your power wiring is also rated for 30A.

Then I must go for some switches for truck or bus. Thanks alot for pointing it out.

In my previous post, I had a DAGU High Power Switch that was giving a very large voltage drop under load, causing my Wild Thumper controller to go into charge mode when trying to climb large objects. After talking with @OddBot, it seemed that the switch was faulty.

I went back to Jameco and purchased another DAGU High Power Switch and installed it in my Wild Thumper. Everything seemed to be working well, and the robot was able to climb things without going into charge mode.

However, when I put the bot on the bench (raised up so that the wheels were not touching the ground) and measured the voltage across the IN and OUT terminals with my Fluke meter, I got some interesting results:

Voltage when idle:

IN: 7.79V
OUT: 7.79V 

Voltage under full throttle:

IN: 7.66V
OUT: 7.53V 

It seems that, under load, the voltage across the OUT terminals is 0.13V less than the voltage across the IN terminals.

Is the switch working as designed, or is this an indicator of another potentially faulty switch? The switch has the same date for QC: 2012-2-7

OddBot's picture

That's normal, any switch, either mechanical or electronic has a small amount of resistance. Even your wires have resistance which is why you need bigger thicker wires for higher currents.

If you look at the data sheet for those FETs their resistance (assuming -10V Vgs) is typically 0.021Ω. As your battery voltage is less than 10V we will assume a resistance of 0.03Ω. There are two FETs in parallel so this halves the resistance to 0.015Ω.

You had a voltage drop of 7.66V - 7.53V = 0.13V. So your current draw would have been about 0.13V / 0.015Ω = 8.66A.

I had to guess the actual resistance of the FETs as they can vary a bit and your Vgs is not the -10V listed in the datasheet. Still, 8.66A / 6 motors is only 1.4A per motor which sound about right if you were holding the platform off the ground with all motors at full power.