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Overvolting for increased speed.

Old 10-24-10, 07:35 AM
  #1  
John Phoenix
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Overvolting for increased speed.

The FAQ for my E-Bike kit says:

" 48V 1,000W eBay kits? I often get questions from customers asking if we carry a 1,000W kit. The simple answer is there is no such thing. It is just a selling tactic. A true 1,000W wheel/motor weighs on the order of 50 lbs. What they are doing is simply overvolting a 500W motor. so that it is pulling the same amount of amps as a 1,000W motor. Our motors can run up to 750W without generating any heat due to over amperage. Keep in mind if you over volt our kits you will be voiding your warranty as our product liability only allows the federal law speed, not to mention that overvolting for higher speeds is incredibly dangerous."

and also:

"Also these kits are capable of running at higher voltages with no modification. Although we will not warranty anything over 36V. At 36V it runs at the correct and safe speed that it was meant for. If you are running at 72V and fry your controller please do not try and return to me as we will know immediately upon opening the speed controller what happened to it."

This tell me I can run up to 750 watts and that the motor is limited now.. it must be below that. ( I don't have a meter to check it yet.. getting one soon) If it can do 750 safely, I want it to.


So.. what happens when my warranty runs out in 6 mo? If this motor can be safely overvolted to make me go say 26 MPH, How do I do that?

Must I buy a new speed controller? Can I adjust this one for higher output? I shouldn't have to according to the info above it seems but I'm new to this and want the Pro's and Con's. Specs on the controller say, 36-60V 22A-35A max.

I want to get a Lifepo4 style battery or the one Amepedbikes sells ( using SLA now) BUT If I am going to spend 3 to 500 dollars on a battery.. I might as well get a speed controller ( if needed) that will make my motor go faster and invest in the 48 V battery - better for the money.

I don't want to go too fast.. just a few more MPH than i'm getting now. I feel the cops won't notice a few extra MPH if that's all I am getting. If this is all true it looks like my 500 dollar kit is turning out to be a better deal than I thought.

Last edited by John Phoenix; 10-24-10 at 08:35 AM.
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Old 10-24-10, 10:24 AM
  #2  
yopappamon
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You really need to stop reading their web site. Lol, just kidding.

The limiting factor for going to higher voltages is the capacitors in the controllers. Most are rated 63v so you are good at 48v battery. I don't know what controller comes with that kit, but you can open the case and look at the caps to see what they are rated at.

Most controllers have a low voltage cutout or LVC. It shuts down the controller when the battery gets low to protect the battery from over discharge. A 36v controller will have the lvc set around 31v. If you just increase the battery to 48v the controller will no longer protect the battery.

You can buy controllers that are rated for higher voltages and that are programmable so you can change the lvc. Edward Lyen sells some very popular controllers over on endless sphere.

48v lithium will be 58.5v fresh off the charger and settle back to 52.8v

Short answer is you should be fine just going to 48v, might check the controller caps. But be sure to get a battery management system (BMS) if you get lithium batteries.
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Old 10-24-10, 11:06 AM
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John Phoenix
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Thanks for the info..

Yeah I know.. I post and read a lot.. Love to learn all I can about E-Bikes.

So.. dropping to 31 volts ( mine is rated at 31.5 ) will be real bad for a lithium 48 V? I just assumed from 52 to 31 would mean a lot of voltage would have to drop before my controller cut out and that sounded like a good thing - means increased range.. But I guess there is something here i'm still not getting.

Also i read about sag - how do amp hour ratings effect this? I have 3, 12 V in series for 36 at 12/AH now.. should I get a battery that's got more AH?
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Old 10-24-10, 11:31 AM
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Lithium can be damaged and ruined if discharged too much. They also do not sag like sla's. So they hold their voltage up until they are close to discharged. And when their voltage drops, it drops very quickly. Too quickly for a person to notice and intervene, so it needs electronics to protect them.

Its something like this, for lifepo4. For each cell, fully charged is 3.65-3.7v, any more charging and the voltage will just spike and ruin the cell. Off the charger they will settle back to around 3.3v, they might sag some on high current discharges due to internal resistance. When they are discharged the voltage will start dropping quickly. Bms systems will shut them off at 2-2.5v, any further discharge will ruin the cell.

On sla batteries the cells average out as you charge the pack, on lithium they will not. Each cell is in a different state of charge and will get full at different rates and can over charge while the other cells are still charging. This is why you need a bms for lithium. It monitor each cell for voltage and bleed off charge when full and shut off the system when empty.

I'm no expert, but this is what I've learned over the last year on these forums. So if I have anything wrong, the experts can correct me.
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Old 10-24-10, 02:10 PM
  #5  
fietsbob
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We used to do that with drag racing Slot Cars, power to strip in track was higher
than the motor's DC V specification,
so they got down the track quite quickly..

then again the motors were not a big investment.
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Old 10-24-10, 10:25 PM
  #6  
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I recommend that if you get into overvolting a motor that you buy a product like the cycle analyst, It will provide you with details like how many amps you motor is drawing, and it can even be used to govern the maximum amps allowed from the controller to the motor.

I overvolted a 24V curried motor to 40volts, and drove it for close to a year without any problem. then, on one fateful day, I cooked the motor by driving into a lot of gusty wind for over an hour.

A stalled motor ( or a motor that is loaded ) draws more current, it I had the cycle analyst, I could have set the maximum amps to 15amps or 20amps, and I'll bet that I'd still be driving with that same motor.
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Old 10-25-10, 07:37 AM
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Absolutely on the cycle analyst.
The only problem is that it's $150!

If your controller can be configured for a max amperage setting, that's alot easier and cheaper than the CA.

My currie (24v) motor has been running on 36v (actually 39.6 avg) for over 3 years. My controller only allows a max amperage of 25a which is at most 900w or so.
Now mind you that is max wattage and not continuous.
On avg my continuous is 37v and 12a which is about 450w continuous which is what my motor is rated at anyways. (450w motor)
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