How To: Installing an MPI voltage regulator

[Grizzly4x4]

My comp buggy gets alot of testing done to it since I just caint leave anything alone for more than a few weeks. After the last comp I made some pretty drastic changes to it in hopes of being able to keep it up with the rest of the competition out there.
One of the things I did was switch to an 11.1V LiPo battery. I did this to lower my center of gravity, lighten the buggy overall, and to give me more punch when I need it.
Ever since I have been running this buggy I have had a Mamba 25 in it from Holmes Hobbies and it has worked great. However, the BEC is pretty weak so I had my steering servo wired directly to the main battery for power while running my dig servo off the Mamba's BEC. With the switch to 11.1V a new setup was neeeded so follow along as I install a voltage regulator to power my servos.

First thing is to solder a connector to the ESC side of the battery plug. I have lots of burned up servos so I just cut the wires and connector off of one. I snipped the yellow signal wire flush with the connector but it wouldn't hurt to just remove the pin.


Here you can see the servo power connector soldered to the male Deans plug .


Next thing you want to do is remove the BEC power wire from the Mamba's receiver plug. You could just cut this wire but I don't like to make permanant changes because I never know when I might want to change things again. Using a hobby knife GENTLY pry up the small plastic lock tabs and remove all three wires from the connector. Be sure to note the order of the wires before you remove them since not all receivers have the same pin positions.


Now cut a length of heat shrink and slide it over the wires. Then fold the power wire back under the heat shrink, be sure that the heat shrink is long enough to fully cover the connector. You don't want anything exposed that might cause a short.


Reinstall the Ground and signal wires into the connector. The finished product should look like this.



Now you are ready for the voltage regulator. I chose to use the MPI ACC234 Heavy Duty Regulator. This sucker is pretty big but it has some really nice features that make it worth it. No it doesn't come with the TLT chassis spacer zip tied to it.
1) A resistor pot allows you to adjust the output voltage.
2) It is rated for 20 watts of power dissapation. (more on this later)


Plug the female connector from the voltage regulator into the power tap on the ESC.


Plug the male connector from the voltage regulator into the slot on the receiver marked (B) or (batt). Before doing this plug a fully charged main battery into the ESC and use a voltmeter to check the output of the voltage regulator at the male connector.


Plug in the ESC to the channel 2 position of the receiver.


Here is what the system looks like outside of the rig.


Here is the system installed in my buggy. The steering servo is plugged into the channel 1 position and the dig servo is plugged into the channel 3 position.




The instructions say that it is designed for 5 cell NiCd/NiMH and 2 cell LIon RX packs but MPI told me that as long as the 20 watts is not exceeded the regulator will be fine.

So what does 20 watts mean?
With an input of 7.2V, and an output of 6.0V; it can handle 16.6 amps of current draw from the servos.
With an input of 11.1V and an output of 6V; it can handle 3.9 amps of current draw.
To calculate this you need to know the voltage drop across the regulator. That is found by subtracting the output voltage from the input voltage [input(V) - output(V)], then divide 20 by that number.
Current(amps) = 20(watts) / voltage drop(V)
For my setup: voltage drop = (11.1 - 7) = 4.1V then current = 20 / 4.1 = 4.88 amps
If I want to draw more current I have to raise the output voltage to be closer to the input voltage. However, the output voltage must always be at least 1V less than the input.

Recommendations:
1) If you want to push your components to the limit running an 11.1V input voltage then I would recommend running 7V output to the servos. This will give you the ability to pull 4.88 amps, which should be good for running a single high torque servo, and some cushion for when the battery is freshly charged. Running servos on 7 volts is pushing it for alot of servos, I have had good luck running Hitec servos at 7-8V but not JR's.
2) If you want to play it safe then I would recommend running a 9.6V input voltage. This way you can set the output voltage to 6 volts and have about 5.56 amps for the servos. This would be a pretty safe setup for rigs that get pack after pack run through them continuously.
3) Absolutely no worries if you run this on 7.2 - 7.4V with an output of 6V.

Because this is a competition buggy I try and push the lightest components as hard as possible since it does not usually see extended use.
If you do this mod your ESC will thank you by running cooler and being more stable.
As I found out, pumping 11.1V into the Mamba 25 while asking it to run the dig servo was really pushing it to the limit; and this was only a Hitec HS-81MG. The little ESC took the abuse but ran very hot and would thermal shutdown if I engaged the dig for very long.

With this setup, testing over the last couple weeks has shown the Mamba runs cooler and should live a happier life. So far I have had no problems with the voltage regulator.

Happy crawling.

Links:

Get your voltage reg, ESC, servos, and motors at:
Holmes Hobbies

MPI links:
MPI voltage reg
ACC-234 instruction sheet

[Badd]

Thanks for posting that Griz . that lipo stuff just drives me nuts . I also ran a regulator with my Mamba 25 . but I am runnin 7cells ,so I just run the cheep Novak regulator .

[Rockpiledriver]

Nice write up Griz.

[Grizzly4x4]

Thanks guys.

This setup may not be for everyone but I thought it might be interesting nonetheless for some. Plus the basic wiring idea should be applicable to other voltage regs.

[TLTCrawlin]

Good idea on the non permanent deal, I def want to do that, so when you go to sell the ESC you can take off the volt reg. and keep it for your new ESC!

[Tanis]

Griz, on the MPI site, are you looking at the specs above or below the ACC234. I don't see where it says 4.8-8.4v input, only that it needs to be 1v higher input than output. I have this reg, and I have been running it with an 8cell batt with no problems. Just wondering if I missed something.

[Grizzly4x4]

Originally Posted by Tanis

Griz, on the MPI site, are you looking at the specs above or below the ACC234. I don't see where it says 4.8-8.4v input, only that it needs to be 1v higher input than output. I have this reg, and I have been running it with an 8cell batt with no problems. Just wondering if I missed something.

This is just above where it says ACC234:
Key Features: • When input is higher than 6V/5.4V, it will regulate output to 6V/5.4V, • When input is less than 6V/5.4V, regulator is bypassed, • Weight only 0.4 oz, • Current: 10 Amp continuous, 20 Amp peak @7.2V input, • Input Range: 4V -8.4V.

This is just below:
Key Features: • Adjustable output voltage, • Large heat sink for optimum performance, • Weight only 1.4 oz, • Current: 15 Amp continuous, 30 Amp peak @7.4V input. • Output voltage range: 4.8-16V. Input voltage must be at least 1V higher than output. Note: Current capacity drops as input voltage increases.

[Tanis]

Ok, I thought the upper was for a different reg. Thanks for the heads up. It has worked for me on 9.6v so far, I will let you know if it fails or not. Nice write up.

Edit: After looking at the specs again, I believe the upper section is a different reg, as it only weighs .4oz and the ACC234 weighs 1.4oz.

[Grizzly4x4]

Originally Posted by Tanis

Ok, I thought the upper was for a different reg. Thanks for the heads up. It has worked for me on 9.6v so far, I will let you know if it fails or not. Nice write up.

Edit: After looking at the specs again, I believe the upper section is a different reg, as it only weighs .4oz and the ACC234 weighs 1.4oz.

Ah ha, I see what you are saying. I was confused because my instruction sheet says the voltage is 4.8V - 8.0V and the website says 4.8V - 16V. I'll edit my post when I am sure of what's going on.

Thanks for the tip though.

[Tanis]

I will be checking to see what you turn up, I can't find my instruction sheet. I want to change my setup if it isn't meant to handle 9.6v input, I don't want to ruin my electronics.

[Grizzly4x4]

Originally Posted by Tanis

I will be checking to see what you turn up, I can't find my instruction sheet. I want to change my setup if it isn't meant to handle 9.6v input, I don't want to ruin my electronics.

Here is a link to the instruction sheet:
http://www.maxxprod.com/pdf/ACC234.pdf

I have sent an email to MPI. I'm pretty sure that as long as the 20 watt power rating is not exceeded then the regulator will be fine. I'll update when MPI responds.

[TLTCrawlin]

my TLT, XRS, 55t, ST125 servo, and futuba 2ch tx/rx,

which one:
ACC134 6-Volt Regulator
or
ACC139 5.4-Volt Regulator

[Grizzly4x4]

Originally Posted by TLTCrawlin

my TLT, XRS, 55t, ST125 servo, and futuba 2ch tx/rx,

which one:
ACC134 6-Volt Regulator
or
ACC139 5.4-Volt Regulator

What voltage of battery will you be using?

[TLTCrawlin]

6c sub C

should I go MPI, or Novak?

[Grizzly4x4]

Originally Posted by TLTCrawlin

6c sub C

should I go MPI, or Novak?

The MPI should work for you, it's rated to 8.4V input volts. The ACC134 provides 6V output and your ST125 is rated for 6 volts so it should work great.

Here is a link to the instruction sheet, it tells you to choose the ACC134 if your servos can handle 6V.
http://www.maxxprod.com/pdf/ACC134-139.pdf

The ACC234 is the only voltage regulator I have used so I caint say if the Novak is a better choice or not for your needs. I can say that I like the quality of this MPI product.

[TLTCrawlin]

Thanks ill look into it, my XRS seems to power it fine, but I stlil might get it incase I run a bigger servo sometime.

[Rckcrwlr]

Great info Griz...I was just thinking of going to regs on my mamba. I think I am going to wait for the Castle Reg.

[Unholy]

The specs on that volt reg are printed backwards everywhere.

The input is 4.8-16 and the output is 4-8.4

I have tested it up to 12 volts input, but didn't have anything above that to test with.

I run 8 cell packs through mine with the output regulated to 7 volts no problem.

I mean think about it... how could the output be more than the allowable input?

[cartronicshn]

Thanks Grizz , i've had a regulator from MPI sitting here for over 6 months because i had no idea how to install it , i will hook it up to my mambas 25 and tower pro 995, i can know run 6-8 cells safely right?

[kris]

I have 4 of these all running on 3cell lipos. I run 1 for each servo on my super and run them to the steering servo on my SW2 and the Hustler2.2 the bec from Mamba max runs my winch servo on the Hustler. There has been a few times after runnig 3 packs in a row through my super you could probaly grill a burger on it but it still works, very good product you will be happy after doing this.