# Motor Mod



## Roy Von Rogers (Mar 21, 2009)

Hi all.

Just ran across an interesting post on the Zap Xebra forum. I will post some of it below, I have no idea what that device could possibly be ...

its a piece of precious metal(the builder tells me)in a sealed housing(abs) with a battery cable coming out each end. You connect it across -1 and -2 lead on the motor. 

There is a solenoid mounted back by the mod/motor/battery area that is switched off and on in the cab with a switch when needed. If you try to take off from a start with the mod on you will feel a extreme lack of power because it is in fact a resistor across the motor leads. 

Anything above 15 mph (approx) you can use it but it really only is NEEDED if you want full speed. At full speed without the mod on all is 'status quo' ....turn it on and it is just like an afterburner ( 6-8mph afterburner )....more speed and the motor just sounds like it has s m o o t h e d o u t somehow and you will get another 6-8 mph. I monitor my discharge current with a very nice shunt ammeter and the ammeter shows more current hense faster discharge.........BUT range is not suffered with the extra high speed. 

So I think the mod tricks the ammeter to think more amps are being used but they must not be because range is not suffering. I think also the key is motor smooths out and you can really hear the difference in the cab. I have a pk. The faster you are going when you flip the switch the more motor smoothing you feel/hear. At 15 mph, light throttle, you might not even know you flipped the switch, except on mine I put a red light on the dash under the switch so I could "see" if it was on. 

I told a dealer about this new and fabulous thing I had found and he said. "That has been done for years. Back in the day guys use to take a roll of romex and put it across the motor and accomplish the same thing". I know it works on 'back emf'. The dealer was not impressed at all but then maybe he does not need the extra few mph this give you. I am a highway user so I really need it to not get run over by a truck on my 4 mile drive home at 45mph ACTUAL. 

The guy that builds these keeps the secret as to what is actually in the abs housing. I guess you could cut it open and see but them may have to have the material tested to know what it is. My guess is it is a rod 4-10 inches long with a cable clamped to each end. The material is probably some carbon/iron/magnesium/copper/gold/alloy (keep guessing) material of some specific % of each at some diameter that is probably important also ??????? I guess if I was going to start manufacturing them I would cut it open and find out. 

For my purposes I don't care what is in it. It works just like he said it would and I was happy to have it. I paid $995 for it. I just looked at my credit card invoice for Oct 09. If the builder builds them for $25.00 then more power him (God bless America). The soleniod is a standard 12v like found on older starter systems 

Does anyone have any idea what this gizmo could be, btw the motor in question is a brushed series type.

Roy


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## major (Apr 4, 2008)

Roy Von Rogers said:


> Does anyone have any idea what this gizmo could be, btw the motor in question is a brushed series type.


Field weakening resistor


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## EVfun (Mar 14, 2010)

Sounds like a field weakening resistor and solenoid to activate it. Shouldn't cost more than $50 to make your own. It does tend to make life a bit harder on the motor controller and if used from a stop could leave the controller unable to effectively limit current at low speeds.


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## Roy Von Rogers (Mar 21, 2009)

I had a feeling thats what it was, but my knowledge on these motors is limited, so I figure I'd ask in here. I do apreciate all the good info from here. Allthough I'm not a dummy where this stuff is concerned, but reading here added a lot to my EV knowledge base.

What type and value would such a resistor be, I'm assuming it reduces some of the emf from the motor and lets it spind just a bit more ??

I'm aware that this should only be done at higher rpm's, as the poster stated. Also what is it that makes it harder on the controller, otherwise not to do it at low end.

I have one of these vehicles, and down the line I will add Lithium to it, at this point I added another agm bringing it to 84v, and it helped a lot, but wouldnt mind doing some field weakening to get it to run a bit easier at the top end, and maybe get a few more mph.

All info is apreciated.

Btw, when I hooked the 7th battery to it and took it for a drive, I knew what an EV grin was all about, that so many in here state . It was the first in a long time that I actually had fun driving a vehicle.

I know that most in here would bother with a Xebra PK, but I got the thing so cheap brand new (4500), I couldnt resist, and figured it was a good starter vehicle to get a feel what EV's are all about. I'm planing on installing 30 200ah TS cells eventually and keeping them charged at 3.5 per cell to keep it within the Curtis controller voltage, and using the vehicle to run local service calls, I may go down to 100ah cells, for I wont be driving a lot of miles per day, but havent made up my mind yet, and since I had major back surgery at the start of this year, I'm a bit slow on the take right now to do anything heavy duty.

Roy


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## major (Apr 4, 2008)

Roy Von Rogers said:


> What type and value would such a resistor be,


Hey Roy,

That's the trick  Knowing that resistance value. And that depends on the field resistance and the degree (or %) of weakening that particular motor can stand before commutation goes to hell. The present motor field would be on the order of maybe 4 to 12 milliohms. If your FW resistance (which includes cable and contactor) was equal to the field resistance, you would divert half the field current and FW it 50%. That may be too much.  

Resistor size (watts) would be determined by I²R, where I is the diverted current and R is the FW resistor ohmic value. You would also want to allow FW bring-in only when the controller is full on and drop-out FW whenever controller starts chopping. FW contactor should be oversized to deal with inductive arcing.

All in all, this is a good way for the DIYer to damage his equipment. The motor, controller, and rest of the vehicle systems were likely not designed to handle this. And you could also enter into problems safety related, like stability or fire hazard.

Regards,

major


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## Roy Von Rogers (Mar 21, 2009)

Thanks major I apreciate the info and warnings. Actually I'm not a diy'er, at least not technically. I work on high voltage eqipment and own a HVAC/Appliance business. I understand your warnings, cause I have the same problem at times in my business, people calling for diy info. I always try to assertain who I have at the other end, and to see if they have any technical talent, at least if he/she says "I have a voltmeter and know how to use it", I at least feel a bit more comfortable giving some basic info..lol.

I'm an old fart (66) and spend my younger years in the automotive field as a professional, and worked on all facets of that field. Used to specialize in the electrical and front end field, cause for some reason most techs were not comfortable with an automotive elecrical system in those days. And have worked on a about everything there is.

I have also spend some time in the electronic field repairing consumer and Ham (amateur radio) equipment, but since getting in to my present business, have fallen a bit behind, and attempting to bring myself up to speed with some of the newer components, which are nothing but discrete devices packaged up, I know its a bit of an understatement, but never the less is so. The only thing new I've seen come up of late are "Memristors", which if brought to fluition could bring our processing cababillties to a quantum leap. Times are facinating, I always have to pinch myself once in a while, cause as youngster I used to read a lot of good scince fiction, and I at times forget, that what was fiction then, I'm playing with today.

I hope I stay around to see a bit more, cause its facinating to a guy like me, who grew up in post WW2 Germany with bombs falling around me, and now I'm a citizen of the best country in the world, doing things I dreamed about when young.

Best regards

Roy


Roy


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