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Updated:  29-10-10

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John Williamson


Powerchair "Control Systems" E.G. Penny & Giles, Dynamic, etc.  If like me you have an interest in these things, since you want power, speed, with huge controllability you will want to learn about the BEST and most powerful available systems.

And importantly the "differences" between them relating to Powerchair performance and control. This page is only concerned with this one aspect.  The manufacturers own sites are a better place to see the "range" of add-on's lighting, actuators, fancy screens and other capabilities. I am only discussing power and control.

Over the past ten or twelve years I have been building my own, or very heavily modifying various different powerchairs because I wasn't happy about their comfort, indoor and outdoor capability, power (torque) or speeds.

Whilst doing this I learned a lot!  I have had very involved discussions with tech guys from P & G (Penny and Giles) who make rather a lot of these controllers! The P and G ones we are interested in here are the top end units such as the Pilot Plus, R-Net controllers. Pilot Plus is still available but superseded by the newer R-Net design. Which is basically the same, but with a fancy screen and more flexibility.  

Controllers and ratings...

These things are sold by every manufacturer in "AMP" RATINGS. In all cases they claim to be able to provide say 100 AMPS to both motors simultaneously. Now while this is true, its NOT the whole story!  I have been doing some digging and measuring.

We all "presume" that this means 100 amps at the 24v batter voltage to each motor. To do that they would need to take 200 amps from the batteries. But when you measure this under a stalled full power condition like when trying to climb a curb and it wont move, its actually 100 Amps from the battery only. Now you cant get anything for nothing so either there is only 50 amps going to each motor or 100 amps at half the battery voltage. HALF the power we expected. Its actually the latter. About 12v at 100 Amps goes to each motor and we don't move up that curb...

The manufacturers conveniently forget to mention that they mean 100 amps at HALF the battery voltage. So in reality the controller is half the real power we expected.

Penny & Giles All of the different Penny and Giles power modules from 50 to 120 amps can output that "Amp rating" to each motor. So a 100 Amp system can provide 100 Amps to each motor at the same time.  While this is happening there is still only 100 Amps at 24v being drained from the powerchairs battery. Now any schoolboy can see that that isn't actually possible unless the motors are receiving half the volts each. So effectively that's what happens. And half the volts means half the number of watts of energy to each motor. And I have measured it. And discussed it with them at length.

 

A 100 Amp Penny & Giles controller can therefore provide a MAXIMUM of 100Amps x 24v = 2400Watts Nominal Power. Or actually less as measured. Half what we are led to expect. Why does this matter? Well it means torque and control is reduced at the very times we require it to climb a ramp or get over a threshold. Not so good.

An R-Net 120 Amp controller can deliver a maximum of 60 amps to the motors, at half the battery voltage. So it has a little more torque and control but only as a "boost" for a short time and its really not a large amount. Effectively that is almost the same as 60 Amps at the proper battery voltage... The same number of watts. 

That is a MAXIMUM total value.   This effectively means that the 100 Amp units are really just behaving like 50 Amps when you need the power on a ramp for e.g. They are effectively only HALF of their rated values once the total possible output is taken into consideration.

This means that when trying to climb a ramp into a van or cross a threshold into a building you only have just 1200 watts per motor (total theoretical) on a 100 Amp system to propel and control you. And that is not really enough for a heavy person in a 6mph powerchair. Forget about doing this in an 8mph chair. Its be even worse.

In reality group 24 Gel batteries like MK's Gel favoured by the industry for e.g. have trouble doing this even when fully charged and new. They really cant do it when old or a little discharged. So your 100 amp Pilot Plus Controller really only gives about 40 real amps equivalent power to each motor at very best... That's why you get stuck on curbs, ramps & thresholds with little power or control in difficult situations. It is a combination of battery voltage dropping and the control systems limited "power" (watts) capability.

The the newer 120 amp R-Net controllers behave in exactly the same but with a 100 amp output that is boosted to 120 amps peak for a short time. (10 seconds) So it can take 120 amps from your batteries and deliver half the power (120 amps at half the voltage) to each motor maximum at the same time. Batteries allowing...  The same applies to VR2 and VSI controllers too! And some of those are just 50 Amps to begin with!

With this in mind I had a lot of email communication with P and G technical guys. After about 1000 words and 4 emails we finally got to the point!

They replied:

Dear Mr

Again, you are absolutely correct in stating that a reduction in voltage will result in a reduction of current. However, please bear in mind some typical values of resistance you might expect to see from a high-specification motor. A value of 0.05Ohms would not be atypical. This would mean that a current reduction would only be experienced at controller outputs voltages below 6V, roughly 25% wheelchair speed.

Best Regards - name removed for P and G.

So the very point where we need power - at the slower end of the powerchairs speed range, for ramps and other difficult manoeuvring operations the power is missing...  Remember this the next time your chair is stalled and will not turn, or go up a curb/ramp without a run up!

 

So how does the Dynamic DX (80 Amp) and DX2 (90 Amp + boost) Systems compare? 

Well there are MANY similarities. These too reduce voltage to the motor at lower speeds and so can also provide the full rated "Amp" capability as claimed, but again at reduced power (voltage). Although under some circumstances the Dynamic systems can actually pull the full rated Amps x2 from the battery. So have more power. (Double the system Watts)

E.g. the Dynamic system (DX2) can actually pull 2x 90 amps from the battery. 180 Amps at 24v. So some 4320 watts total power capability (claimed but not measured. So unlike the P and G system it is not limited to only 100 Amps (120 on boost?) from the battery (or just 2400 watts).

It can only do this however at the point where the motor voltage is at "full 24v" and not demanding more that 90 amps per channel. And so at about 1.5 mph or above. And as soon as demand increases on say a hill the full power is scaled back to a lower level.

An email here from Dynamic:

Hello John

The maximum current from the battery for the DX2-PMA90 is 180Amps. This is split 90A per motor. This will ONLY be achieved into a true 90A load at maximum speed demand. If you reduce speed, you will not get the maximum power output. If you increase load (increase the current) above 90A (current limit) you will not get maximum power. Above 90A, the power reduces through reduction in motor voltage in order to limit current.


Best regards - name removed.

So they both do the same tricks at the slow speed end of things, but dynamic "claim" that they can supply full power (2x the rated amps) and draw 180 amps from the battery. Although I actually think that the guy is mistaken.

So in real world use with Gel batteries there will be little benefit anyway as they cannot give this amount of power. However swap batteries to Odyssey or Optima AGM batteries that can actually produce this much current (amps) and the benefits in torque and power, especially off road and ramps, or with tall gearing are obvious to any spirited user.

So, if you are buying a new powerchair, which is the best system?

The maximum number of total watts your controller can provide is very important.  MORE is always better even if you never actually use them or need that extra torque to turn or climb a ramp. They are simply a "reserve" of power for the odd occasion that its important. This is not the same as "amps". What matters is the total system power.  

But for a manufacturer to fit a "big" Amp controller they need to make sure that the batteries and battery cables can and will survive that bigger load. And that the motors and gearboxes have enough strength to survive the extra torque. And that in fact a stalled or almost stalled motor actually draws that much current. Meaning in some cases a heavier motor.

All of which ads up to COST for them...  Bear all of that in mind when looking at powerchairs. Then you will see why some chairs have 50 Amp controllers... You want the BIGGEST Amp controller you can get for the best performance on ramps etc., while maintaining safe control. All of this stuff above is subject to Correct Programming!

 

And as we saw above its not even that simple because some systems do not do what it says on the tin, or they do "technically" but at lower voltage. So you don't get the power you expect.  Hence this table below so you can see what is what!

SYSTEM - Read details its very important!  - Some systems have HALF their expected power!  Especially check out the Dynamics Systems.


Penny & Giles -
Pilot Plus
100

 
100 Amps
Total System Maximum from batteries, or 100 to each motor but at half the voltage. So half the power. Total max system power 2400 watts.

Oops - this is why thresholds and steep ramps are difficult with loss of control at times.


Penny & Giles -
Pilot Plus
80

 
80 Amps
Total System Maximum from batteries, or 80 to each motor but at half the voltage. So half the power. Total max system power 1920 watts.

Oops - this is why thresholds and steep ramps are difficult with loss of control at times.


Penny & Giles -
Pilot Plus
50

 
Don't bother!


Penny & Giles -
R-Net 120
 
100 Amps Total System Maximum but with 10 second extra 20 Amp "boost"
from batteries,
or 100 to each motor but at half the voltage. So half the power. Total max system power 2400 watts. (with 20 percent boost for 10 Secs.)

However maximum is 1200 Watts to each motor simultaneously!  Oops - this is why thresholds and steep ramps are difficult with loss of control at times.  This systems has fancy colour screens and added gadget inter-connectivity but otherwise is much the same as the Pilot Plus System with an added short term "boost" capability. And a small gain in efficiency.


Penny & Giles -
R-Net
LOW Amp Output

 
Don't bother! Use the R-Net 120.

Dynamic DX 80  
160 Amps Total System Maximum
from batteries, or
80 Amps to each motor simultaneously!  But only at the speed that means the motors draw rated current. Better for control. But as speed is reduced the same voltage reduction applies as in the case of P and G systems. So that means no gain in actual stall torque over P and G systems. Although PEAK watts is 3840 (If their statement above is correct).
 
Dynamic DX2 90  
180 Amps Total System Maximum from batteries (claimed), or 90 Amps to each motor simultaneously!  But only at the speed that means the motors draw rated current. Better for control. But as speed is reduced the same voltage reduction applies as in the case of P and G systems. So that means no gain in actual stall torque over P and G systems. Although PEAK watts is 4320 (If their statement above is correct).
 
Penny & Giles -
VR2 50, 60, 70, 90 Amp Systems
 
50, 60, 70, 90
Amps Total System Maximum from batteries, or full rate amount to each motor but only at HALF the voltage when high current is demanded.  Only the 90 Amp unit is worth looking at for low end Powerchairs.

However maximum is HALF power to each motor simultaneously!  Oops - this is why thresholds and steep ramps are difficult with loss of control.
 

Penny & Giles -
VSI 50 Amp Systems
 
50 Amps total. 25 Amps to each motor simultaneously.

Don't bother unless you are very light and 103 years old...  My model helicopter uses a 60 amp with 80 amp "boost"!!!  And I am not sat on that...
 

 

Added, By JoeC in the forum and moved here as its useful info for many:

"Qtronix is just a re-badged P&G Pilot+. The programmer is the same, the connectors and plugs are the same, as far as I can tell only the mould they used for the joystick housing is different. Oh, and any stickers or decals- which is what I meant by re-badged."

"In my experience, a lot of the Dynamic DX module that I bought on EBay were originally installed in Pride chairs. Some of these chairs are rated for users up to 500 or 600 pounds, so they really couldn't cut corners on the electronics or the chair wouldn't be able to get over the threshold out of the showroom".

"It should be noted that Invacare owns Dynamic, and some of the controllers in Invacare chairs are based on controllers you see described on the Dynamic website. The Gearless Brushless controller appears to be made or designed by Dynamic, and some of the MK-5 controllers I have seen on EBay appear to be based on Dynamic Shark controllers (a lower end model that's more on par with the P&G parts)."

A forum post discussing this is here - one of many! Sign up to ask any questions

More to come asap!!!

________________________________________________________________________

[Image]And FINALLY after messing about designing my own chairs for the last 13 years and getting sick to death of a total lack of power from the industries hi end Controllers I decided to do things my own way as usual.

On the 28th of Sept 2010 I ordered a ROBOTEQ True 150 Amps per channel Robotics controller for these reasons.

It actually truly gives you 150 real amps per channel. No reduced voltages to "share" the power.300 real Amps total from the batteries. And it is happy to work from 10 volts right up to 50 volts.

I plan to use 36v and three Odyssey batteries to start with. That means a true 6000 watts of power to work with. Finally!

www.roboteq.com and my controller is this Click for specs and PDF manuals etc. At last I can stop messing about with gutless mobility products!  This is going in my generation 3 hi speed 12 mph powerchair.

It will be used on the MK3 Version 45V and 15 mph! of my home built powerchair!

 

 

 

 

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