Field weakening

GEM Forum
1

Rather than hijacking the 29mph thread, I’m starting a new one.
May on be of interest to only a few.

Testing results of field weakening “only” on T4 7.5hp.
Top speed on level ground = 34mph with MM1/2. 12/1 gears. Stock tires. Poor batteries.
Max arm amps 245.

Stock setting is 65 = 2.1 amps.

External circuit reduces minimum F current 25%. 1.6 amps minimum or equivalent setting of 62.

Seems field weakening alone does not produce noticeable results on my Gem.

I have not reprogrammed F7 to 62 for a test of my circuit math.

Would this be expected result. Going from 65 to 62?

2

After more testing. Seems I gain 2mph when I flip the FW switch.:clap2:

3

65 to 85 are common setting for a 5 hp I go to 60 on a 5 hp 55 on a 7

4

Thanks.
Just so you know, not changing the settings.

I’m listing calculated equivalent settings.

My test may not mean much, already going faster than is safe for motor.

Should I expect anything other than higher speed?

5

YES MUCH better performance gives more amps accelerating.

(2) ways to limit speed 1 limit amps and reduce performance. 2 Keep amps and use the speed limiter.

2 is what I use. Cart maintains performance when passengers are added.

6

Good news then.

I’ll keep at it. See if I can get better acceleration.

Can only test a few passes. Batteries are weak in 2008.
2010 has the wheel off.

Remember, I’m weakening field only.

7

Dave

You do have the 2X MM installed - right?

Rodney

8

Yes I do.
I’ll keep play with the field until something happens.

9

lets clearify a few things .
Dave,
I real world changing from 65 to 62 gives you only a small increase in speed. going all the way down to 55 might give you 10% . the biggest change is fooling the speed controller ( like your mm does) or by changing rolling radius or gear ratio .

i’d like to hear about how you are externally dropping you field current. between this and your mm your doing some unique things .

shunt motors love voltage , thast why they slow down so much when batteries get low . they can get the amps but not the volts . my guess would be if you were to add a 6 volt battery in series with your 72v batteries and charge the whole thing to 84 volts instead of the current 77.4 (12.9X6) your cart would accelerate faster then all of the controller mods combined .

Rodney,

fyi changing #7 does not give the motor more amps, it changes the field ratio so the motor rpm’s increase giving you more top rpm . you do give up a little torque in the top end but its not very noticeable .

10

The MM is simple. Does exactly what high speed magnet does.
Spoof controller into seeing 1/2 speed.

By being totally electronic, I can customize to read a % lower. 20% for example.

That will protect motor from over revving, as it will still limit at 30mph. 25 on speedo.

Also can make speed read correctly from 1-22 then switch to 1/2.
The controller then sees stock performance until overdrive.

Or if needed, switchable, turn it on or off.

11

The FW is just in testing stage. I have no real experience with FW changes, so don’t know what to expect.

While testing, I have a switch in cab.
I can weaken field at any time while driving. This is a % from stock curve.

Very conservative so far. If I blow something up it will take the fun out of it.

My first idea is to make an add-on to MM, that will weaken field at a set RPM when an overdrive switch is “on”.

While it may be of little use to programmers, it may find a niche with diyers.

Or possibly T3 users.

I lack something to test it on. My 7hp T4 is peppy and fast now.:frowning:

12

[quote=kinghappy;29289]lets clearify a few things .
Dave,
. my guess would be if you were to add a 6 volt battery in series with your 72v batteries and charge the whole thing to 84 volts instead of the current 77.4 (12.9X6) your cart would accelerate faster then all of the controller mods combined .
.[/quote]

That is on my to-do list for my doggy 48v tomberin if programming doesn’t help.:slight_smile:

13

I really want to do the 6v add on battery thing on my e2 , but I cant find a 6v gel battery that isn’t a monster. may have to try and find a used 6v gel monster and just prove concept.

the lithium pack I run keeps voltage much higher then the gels , the difference in acceleration and top speed compared to a stock cart and even a reprogrammed stock cart is pretty amazing .

it did over 40mph with a stock 5hp motor and I never have an over heat problem .
so i’m pretty sure adding more volts to a stock battery setup would work well .

14

My plan is to add a lithium cell or two.
Single cell chargers are common. It would have more capacity than other batteries, so it would not need to be monitored closely.

15

[quote=Inwo;29303]My plan is to add a lithium cell or two.
Single cell chargers are common. It would have more capacity than other batteries, so it would not need to be monitored closely.[/quote]

so you would setup the onboard to just charge the 6 gels , then put the lithium at the end of the series and charge it with its own charger?

as long as the gels would discharge quicker then the lithium it should work .

Dave you have some very creative ideas!

16

Yes, and there may be ways to spoof the controller into accepting even more voltage. The accessories could remain connected to 72v.

I would do better with service information on controllers.

17

Appears voltage is sensed on Pin1.

18

[quote=Inwo;29309]Yes, and there may be ways to spoof the controller into accepting even more voltage. The accessories could remain connected to 72v.

I would do better with service information on controllers.[/quote]

have you downloaded the available info from flight systems ?

the t4/t5 can accept up to 86v and I know from experience the dc to dc converter well operate at that level

19

[quote=Inwo;29303]My plan is to add a lithium cell or two.
Single cell chargers are common. It would have more capacity than other batteries, so it would not need to be monitored closely.[/quote]

I take that back. Having trouble finding them now.

6 months ago, I got this quote:

Hi
Pls check pictures, 10A and 20A are the same appearance.
The quotation for 3.65V 10A charger:
100 pcs ---------18USD/PCS
200 pcs -------16 USD/PCS

The quotation for 3.65V 20A charger:
100 pcs ---------28USD/PCS
200 pcs -------26 USD/PCS

Are these aluminum case with fan?—Yes.
Pls advise me your quantity.

Thanks Amy

Usually, they will send samples for same price. Shipping would be a big deal.

Can’t find then on Ebay anymore.

20

Losing confidence as aux. FW has no effect.

To check, I lowered F7 from 65 to 60. Can’t really feel a difference.