Speedboost using +6V instead of +12V battery in series?

[ProDigit]

Hi,

I have an XTreme XB-700Li bike, with 700W motor and 48V 20Ah battery pack in by bike, and have a second 48V battery pack 10Ah in parallel. Both batteries have a BMS, run without diodes, and so far it runs without problems.

I just wanted to make a 6V battery, 30Ah, to put in series with my battery packs, to boost speed.

I've read about shunt mods, which are not necessary for me, as the 700W motor is powerfuil enough to propel my 160LBS skinny ass over mostly straight roads; and also read about speed mods.
The speed mods on the bikes, usually go with their standard (eg:48V) + 12V battery in series with the stock battery. I've heard that 12V could damage the controller in the long run.
I don't want to damage my bike, and wonder if it perhaps better to boost volts in the +6-+9 range, rather than +12 range...

For that I will need to build my own battery pack, with BMS. I'll also need a charger that will charge this battery.

I'll probably use a fuse system (240/400V 30A), to disconnect the 6V battery while charging, and switch it on whenever I want to make use of the speed boost.

Would it make sense boosting the voltage so minimal? (I'm just hoping to have ~5MPH speedboost if possible).

And if it would do the trick, I'll need some help in choosing the right materials.

I can get regular lipo cells pretty cheap. I can solder them together.
All I need is a BMS that operates on these voltages, and a charger, that can charge the pack.


Where do I start looking for the right materials (which site sells them)?

You think this mod is a good idea?

 

[docnjoj]

Not a great idea! Just by paralleling a 10 ah and a 20 ah you reduce the availible mileage by half. You need to use a 20 ah batt to parallel, otherwise you have emasculated your 20 ah by half! Parallel batteries should have fairly equal amp/hours.
otherDoc

 

[ProDigit]

Not a great idea! Just by paralleling a 10 ah and a 20 ah you reduce the availible mileage by half. You need to use a 20 ah batt to parallel, otherwise you have emasculated your 20 ah by half! Parallel batteries should have fairly equal amp/hours.
otherDoc

I've extended the range, not reduced it.
The secondary battery provides more power, and leviates the pressure on the primary battery in acceleration. Essentially I made a 30Ah battery, but that is not really the question now,

The thing I want to know is if putting a battery in series with the internal battery, is a good idea or not; regardless of the internal batteries.

 

[dogman dan]

??? Adding 10 ah 48v to 20ah 48v in paralell gives him 33% more watthours. 33% more range. You are thinking in series doc.

But adding 6v more depends on the controller. Chances are, you got 63v caps. Chances are, your battery charges to 58v. So add 6v more, and you are running 64v. But only for a few minuites. Ride that bike for 1 mile, and you are bound to be down to 55v or so, and then adding 6v more at that time should be fine.

But you'll only see a very small increase in performance. 300w more. So a bit perkier up a hill, but only about 2 mph faster. Nothing wrong with getting all the performance you can out of it. 8) It would make your bike ride like it's fresh off the charger for longer.

 

[ProDigit]

??? Adding 10 ah 48v to 20ah 48v in paralell gives him 33% more watthours. 33% more range. You are thinking in series doc.

But adding 6v more depends on the controller. Chances are, you got 63v caps. Chances are, your battery charges to 58v. So add 6v more, and you are running 64v. But only for a few minuites. Ride that bike for 1 mile, and you are bound to be down to 55v or so, and then adding 6v more at that time should be fine.

But you'll only see a very small increase in performance. 300w more. So a bit perkier up a hill, but only about 2 mph faster. Nothing wrong with getting all the performance you can out of it. 8) It would make your bike ride like it's fresh off the charger for longer.

Thanks for the advise.
I wished I would have some table where I could see how much voltage increase I need to gain 5MPH.
I don't want to go too crazy.
Most people who have the lower powered XB-600 where able to get a good 10k miles out of their controller before the caps gave in; and that is with the 60V mod (in other words adding +12V).
Perhaps indeed the caps are only rated upto 60V, but they're flexible. Not to be ran all the time at that voltage, but like you said, the voltage drops anyway during acceleration and driving. The only time they will be handling over 60V is when the bike gets turned on, without acceleration or load.
Even then, just turning on the lights would drop the voltage somewhat.

also, according to my calculations adding a second battery of 6V in series would increase performance only by upto 120W, not 300, as the controller mostly limits the current, not the voltage. In other words, if my 700W motor would be running at 48V, 20Ah full acceleration, it would now be running at 20Ah, 54V.
that's from 960W to 1080W, or an increase of 11%.
That's 11% more torque, but I don't know how that translates to speed;
Even if speed would increase by 11%, it would only get me from 23MPH to 25.5MPH at best.
I guess that's kind of the formula.
In order to double speed, watts would need to be doubled; so my 5MPH speed increase from 23 would mean a 21.7% increase in power, or going from 48V to 58V (or have a 10V battery connected to it).

Without the right calculations, I only presume it must be something like this; in which case I can forget about 5MPH, unless if I would do more than one improvement (eg: put larger tires on it, increase voltage to +9V, and do a shunt mod, to get more torque out of it...)..

I wanted it to be a small project though....

 

[docnjoj]

??? Adding 10 ah 48v to 20ah 48v in paralell gives him 33% more watthours. 33% more range. You are thinking in series doc.

But adding 6v more depends on the controller. Chances are, you got 63v caps. Chances are, your battery charges to 58v. So add 6v more, and you are running 64v. But only for a few minuites. Ride that bike for 1 mile, and you are bound to be down to 55v or so, and then adding 6v more at that time should be fine.

But you'll only see a very small increase in performance. 300w more. So a bit perkier up a hill, but only about 2 mph faster. Nothing wrong with getting all the performance you can out of it. 8) It would make your bike ride like it's fresh off the charger for longer.

Hmmmm.........Soyou guys are saying that a 10amp plus a 20 battery // will give more range that in series. This must mean that the batteries will draw down at different rates so 1/3 for the 10 and 2/3 for the 20? Is this actually the case?
otherDoc

 

[ProDigit]

??? Adding 10 ah 48v to 20ah 48v in paralell gives him 33% more watthours. 33% more range. You are thinking in series doc.

But adding 6v more depends on the controller. Chances are, you got 63v caps. Chances are, your battery charges to 58v. So add 6v more, and you are running 64v. But only for a few minuites. Ride that bike for 1 mile, and you are bound to be down to 55v or so, and then adding 6v more at that time should be fine.

But you'll only see a very small increase in performance. 300w more. So a bit perkier up a hill, but only about 2 mph faster. Nothing wrong with getting all the performance you can out of it. 8) It would make your bike ride like it's fresh off the charger for longer.

Hmmmm.........Soyou guys are saying that a 10amp plus a 20 battery // will give more range that in series. This must mean that the batteries will draw down at different rates so 1/3 for the 10 and 2/3 for the 20? Is this actually the case?
otherDoc

Both series and parallel connection will give you extended range.
Parallel connection will result in greater torque, better battery load; and greater mileage when the same torque is applied as with a single battery.
Series connection will result in greater speed, slightly lower torque (torque is limited to the lowest amp battery in the chain); and greater mileage due to greater speed. Mileage is linear to the Watts that the battery connection provides. In my case a 20A and 10A battery, each provide ~960W and ~480W is a total of ~1440W.
Parallel connection will stress individual batteries less, and when one battery goes into low voltage shut down, one can still drive on the other battery; unlike series connection where if one battery shuts down, the whole bike shuts down.
Series connection are actually better for high RPM motors with low Torque. Most Xtreme XB bikes have a low RPM, high torque motor, that's speed limited; which means they're more made for towing, than for speeding (or, they will handle a battery parallel connection better than a series connection).

With high rpm motors (usually also brushed motors), doubling the voltage, usually doubles the speed. It does not seem to be the case with the brushless motors used in the Xtreme bikes; where doubling the voltage, would increase torque significantly, but not really double the speed (only marginally increase the speed).
I guess because the motor is controller limited.

 

[Jeremy Harris]

Both series and parallel connection will give you extended range.

True, at the same speed, not true if you use the extra speed that series connection may give, as power is pretty close to being proportional to the cube of bike speed. Double the speed and you use roughly eight times the power.

Parallel connection will result in greater torque, better battery load; and greater mileage when the same torque is applied as with a single battery.

True, but only for the rare case where the battery internal resistance is providing the current limit. Usually the controller limits current and hence torque.

Series connection will result in greater speed, slightly lower torque (torque is limited to the lowest amp battery in the chain); and greater mileage due to greater speed.

Sort of half true. If the controller is doing its job, then torque will be the same, as it is set by the controller current limit.

Mileage is linear to the Watts that the battery connection provides. In my case a 20A and 10A battery, each provide ~960W and ~480W is a total of ~1440W.

Not quite. Range at any given speed is determined by the energy in the battery, which is either measured in joules (watt seconds) or more commonly in Wh (watt hours). Power is measured in watts, and is given by the product of voltage and current.

Parallel connection will stress individual batteries less, and when one battery goes into low voltage shut down, one can still drive on the other battery; unlike series connection where if one battery shuts down, the whole bike shuts down.

Sort of, depending on how the BMS in each battery behaves and how the packs are wired together. If the packs are paralleled with diodes, then both BMS unit sshould behave like this - if not then smoke is a possibility if one pack runs to shut-off.

Series connection are actually better for high RPM motors with low Torque. Most Xtreme XB bikes have a low RPM, high torque motor, that's speed limited; which means they're more made for towing, than for speeding (or, they will handle a battery parallel connection better than a series connection).

With high rpm motors (usually also brushed motors), doubling the voltage, usually doubles the speed. It does not seem to be the case with the brushless motors used in the Xtreme bikes; where doubling the voltage, would increase torque significantly, but not really double the speed (only marginally increase the speed).
I guess because the motor is controller limited.

Sort of half true, half untrue. Both permanent magnet brushless and brushed motors follow exactly the same laws, so behave the same way. Losses may be slightly higher in some brushed motors, but generally there's not much to choose between them. Doubling the voltage will only increase torque if the motor winding resistance is such as to be limiting maximum current, rather than the controller. This can just about happen with some hub motors, those that have a high winding resistance, when they are run on low voltages.

 

[wesnewell]

Lots of misconceptions here. Paralleling batteries will only extend range. It will not increase torque or speed unless the single battery was sagging dramatically under load. If you want to increase torque (acceleration) you'll have to increase the amp output of the controller.
Adding 6v to a 48v system will hardly be noticeable. You need to add at least 12v, and 24v or more for significant improvement. More than likely, this will also require replacement of the controller. If you series in another battery pack, it should be of the same ah as the current one so they will discharge evenly. And while you can get a 24v pack with charger, I'd replace the whole pack and controller with a 72v system. A 15ah 72V system will have the same range as a 20ah 48v system at the same speed. As a general rule, increasing amps increases torque, while increasing voltage increases torque and speed.

 

[ProDigit]

Today I was riding with my extension battery, both fully charged for the first time,
I reached top speeds of ~23,6MPH on a flat, and 24,8MPH downhill.
When I was driving I noticed when my speed dropped below 22MPH, it got too slow.
Newly charged the speed averages between 23,6 and 23,8MPH (measured on a cyclometer,not the bike's speedometer, which displays speed incorrectly).
At 75% battery, the speed averages between 23,1 and 23,4MPH.

On 35MPH roads, driving at nearly 24MPH is quite ok, since I accelerate faster than most cars, and by the time they're going 30MPH, to overtake me, I'm already at the next stop light. Driving at 23MPH on average, and dropping to 22MPH does NOT feel ok.
Likewise driving at 24,6MPH makes me feel much more secure. While driving I thought that if I could only gain 2-3MPH, I'd be more than satisfied!
A +5MPH speed gain is something I hope to achieve with some improvements on the bike!

For that reason I want to find a high capacity 6-9V LiPo battery; preferably 30Amps, and use a bi-polar switch. In position one, the battery gets routed straight to the controller; in position 2, it gets routed via the Extension battery.

If my calculations are right, a 6V battery in series should give me a top speed of ~26MPH, and a 9V should give a top speed of ~27.5 MPH.
It seems worth it to me,to gain these few MPH's!
On a 35MPH road, I would feel more secure to drive 26MPH, than 22MPH; even if the 4MPH makes very little difference, if it's just enough to keep most cars behind me, instead of having them overtake me at every chance!

So, where would I find a good BMS, that would be able to handle a 6 (or 9)V 30Ah battery?
And where would I be able to buy a charger for these voltages?

Thank you!

 

[dogman dan]

Look for 2s A123 packs for various devices like a roomba. Size it at 35 ah, and you cannot run it out before you finish off 30 ah. Or get 4, 20 ah A123 pouch cells.

Charge it with an RC charger.

You are only going to see about 2 mph more speed. But that will get you that 24 mph.

 

[ProDigit]

Look for 2s A123 packs for various devices like a roomba. Size it at 35 ah, and you cannot run it out before you finish off 30 ah. Or get 4, 20 ah A123 pouch cells.

Charge it with an RC charger.

You are only going to see about 2 mph more speed. But that will get you that 24 mph.

Freshly charged I'm already going 23,5MPH!
Today I drove until 50% empty (on the internal meter), and I was still going 22,5MPH!
That was after driving a good 2 hours stop and go traffic.