more volts better?

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flippy   10 kW

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more volts better?

Post by flippy » Mar 12 2018 4:54pm

the time has come that i need to decide on what to do in life.

right now i have a nice 16S25P battery.

but the little voice in me is saying i need to rip apart the entire pack and rebuild it into a 21S19P battery. that voltage is at the limit of the controller (regular KLS7230)

the goal for me would me that i can keep on cranking volts into that 1.5kW hub motor (it is a V2, so not that bad)so i can set som serious speed going. i hate being stuck at 45kph all the time.

im just wondering if the battery upgrade the best way to do this (going from 57v right up to 88v). i lose amps going from the battery to the controller but how will the controller respond to the motor? will the accelecration take a dive off the line?
is effieiency out the window when running a 48v motor at 72v?
second option would be to spend some peso's and order a 3kW QS motor with all the bells and whitles on it.
i already have a govecs to play with that goes to 115v. and i like these higher voltages a lot better then messing around with 50 kilos of car batteries onder your seat.
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Re: more volts better?

Post by billvon » Mar 12 2018 5:16pm

flippy wrote:
Mar 12 2018 4:54pm
the time has come that i need to decide on what to do in life.

right now i have a nice 16S25P battery.

but the little voice in me is saying i need to rip apart the entire pack and rebuild it into a 21S19P battery. that voltage is at the limit of the controller (regular KLS7230)

the goal for me would me that i can keep on cranking volts into that 1.5kW hub motor (it is a V2, so not that bad)so i can set som serious speed going. i hate being stuck at 45kph all the time.
Have you considered a phase-advance controller?
--bill von

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Re: more volts better?

Post by amberwolf » Mar 13 2018 2:08am

flippy wrote:
Mar 12 2018 4:54pm
but the little voice in me is saying i need to rip apart the entire pack and rebuild it into a 21S19P battery.
Unless you also lower the current limit of the controller, then it will now be harder on the battery assuming the controller still pulls the same current at startup or under heavy loads.

im just wondering if the battery upgrade the best way to do this (going from 57v right up to 88v). i lose amps going from the battery to the controller but how will the controller respond to the motor? will the accelecration take a dive off the line?
The cell groups will sag more in voltage, assuming the controller still draws the same current, because there are less of them in parallel.

But the total voltage will be higher, so it's likely that WOT from a stop will cause quicker acceleration because you'll have a high current for a longer time (takes longer for enough BEMF to be generated by speed to lower the motor currents).

You can play with the http://ebikes.ca/simulator with a similar setup (if yours is not in there) to see exactly what happens. Use the A vs B setup to compare a before/after version of your bike.

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flippy   10 kW

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Re: more volts better?

Post by flippy » Mar 13 2018 3:11am

billvon wrote:
Mar 12 2018 5:16pm
Have you considered a phase-advance controller?
i already have a KLS7230. plently of grunt to blow the coils out of the motor. going to the voltage limit of the controller seems like the most logical step for more speed. buying a new controller is a much more expensive step then rebuilding the battery.
amberwolf wrote:
Mar 13 2018 2:08am
The cell groups will sag more in voltage, assuming the controller still draws the same current, because there are less of them in parallel.
But the total voltage will be higher, so it's likely that WOT from a stop will cause quicker acceleration because you'll have a high current for a longer time (takes longer for enough BEMF to be generated by speed to lower the motor currents).

You can play with the http://ebikes.ca/simulator with a similar setup (if yours is not in there) to see exactly what happens. Use the A vs B setup to compare a before/after version of your bike.
i am not worrying a lot about voltage sag. it will sag some, but the 19P setup can deliver 180A continous so i am not worried about that. when sag becomes an issue i am probably already well beyond 30mph and need to ease off anyway.

i will ease off the current a bit to compensate for the higher voltage but do you think it would accelerate faster or slower?

i know about that tool, but it is basically useless for anything but bikes. i have a scooter with a 10" hub motor.
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Punx0r   10 GW

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Re: more volts better?

Post by Punx0r » Mar 13 2018 3:32am

It should be quicker if you're not presently hammering your battery (which it sounds like you're not) because as Amberwolf said, the controller will be able to provide peak current to the motor for longer as you accelerate.

I'd do it. You should see a ~40% increase in top speed and acceleration should continue to pull hard at your current top speed of 45kph.

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flippy   10 kW

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Re: more volts better?

Post by flippy » Mar 13 2018 4:12am

weird thing is that previously i had a 13S battery and got about 42km/h with a fresh charge but when i rebuilt the battery to 16S the top speed only increased by 4~5km/h not the 10km/h i expected. is this due to having a crap motor? or just bad luck? the hub motor is a V2 so the quality is not that bad. will jumping to 19S really give that boost in top speed i want? i just want 50km/h all the time instead of 47 off the charger and dropping to 40ish when near empty.

(and yes, i already fitted the biggest tire i can fit)

so my question is that the original motor is 48v. cranking up to 60ish only gained me 4~5km/h. will jumping up to 80v really do something or will it just kill the efficency?
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Re: more volts better?

Post by amberwolf » Mar 13 2018 1:23pm

Check it with the simulator--it'll give a result that's close enough to give you the idea whether it'd do something like what you want.

It's useful for any hubmotor-powered land vehicle; the fields that are bike-specific can either be disabled or set to custom values that emulate your particular vehicle. (just because it doesn't have a preset for you doesn't make it useless; it just takes more work to get your results).

If your motor isnt' listed pick one you knwo (or think) is close.

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Re: more volts better?

Post by Punx0r » Mar 13 2018 4:38pm

yeah, do give the simulator a try - it will give you an accurate answer if your motor is in there.

When you went from 13S to 13S did you maybe have more sag? Even if you don't, the increase in speed won't be proportional to the increase in battery voltage as the motor is more heavily loaded at higher speed (greater aero drag) and as we know, when you load down a motor it's speed drops.

FWIW last time I changed voltage on the same bike/motor I went from 12S to 18S (with a couple of volt or two more sag) and went from 30 to 40mph (rather than the ~45mph expected).

You want to have your top speed a good bit above you normal highest cruising speed, or getting there and holding it there (hills, headwind) becomes a pain. Bear in mind your controller is probably good for just under 100V - if your motor can take the load at high speed!

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Re: more volts better?

Post by John in CR » Mar 13 2018 10:15pm

I can't imagine any vehicle where riding at WOT is the norm. You'll love the higher voltage, but is 55kph or so really going to be enough, since 45 isn't? Your wh/km will increase significantly since wind resistance goes up geometrically with speed.

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Re: more volts better?

Post by flippy » Mar 14 2018 8:15am

John in CR wrote:
Mar 13 2018 10:15pm
I can't imagine any vehicle where riding at WOT is the norm. You'll love the higher voltage, but is 55kph or so really going to be enough, since 45 isn't? Your wh/km will increase significantly since wind resistance goes up geometrically with speed.
yes, technically i want 51 to be the top speed at all times, even when the battery drains. that is the legal limit (with added correction).
no, i dont need to have more speed then that as the fines are loudicrously high and it's a daily driver, not a fun machine for the weekeinds. i just want to be at the legal limit for speed. acceleration is not legally limited so i can have all the fun in 0-51. that said, i do want it to make it to 51 in the first place, not just fresh off the charger on a warm day.

power consumption is not an issue. i have 4.2kWh and one trip to work is 2~2.5kWh depending if i use the heated gloves and 55W HID lights :roll:

ps: what do you mean with "WOT"?
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Re: more volts better?

Post by Punx0r » Mar 14 2018 9:20am

"Wide Open Throttle" i.e. full throttle

The problem is that if you want to be at 51kph all the time, even when the battery is drained, or if there is a gentle hill, or if there is a head-wind, or if it is a cold day, then the bike needs to be capable of going faster. Probably at least 60kph on warm day/flat road/full battery/no wind.

This is a problem if the law says your bike cannot exceed 51kph. I think the only way would be to have a 60+kph bike but with a speed-limiter set to 51kph. Then you can just hold full throttle (WOT) all the time and keep cruising at 51kph, even if there are hills etc

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flippy   10 kW

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Re: more volts better?

Post by flippy » Mar 14 2018 9:58am

Punx0r wrote:
Mar 14 2018 9:20am
"Wide Open Throttle" i.e. full throttle
This is a problem if the law says your bike cannot exceed 51kph. I think the only way would be to have a 60+kph bike but with a speed-limiter set to 51kph. Then you can just hold full throttle (WOT) all the time and keep cruising at 51kph, even if there are hills etc
thanks.

and yes, this is my goal. i already have a button wich basically works as WOT (it puts 5v on the trottle signal) unless the brake is pressed as my commute is mostly long roads so keeping the trottle open for long is annoying. being able to keep 51 at all times is not a problem for the battery as it has overkill capacity and current rating and i can set the max rpm in the controller. i just want to shave off as much off my commute time as much as legally allowed. so that means maximum acceleration (as long as the motor doesnt turn into plasma) and hitting the actual speed limit at all times as fast as possible. i recon i can gain 15 minutes off my commute this way.

rebuilding the battery is no problem as building custom batteries is my (side) business.

my slight worry is the motor. i do not know how it will like having shoved 80V into basically a 48V motor.
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Re: more volts better?

Post by Punx0r » Mar 14 2018 10:27am

With the rpm-limiter in the controller it sounds like the system would do what you want. John may be able to advise what theoretical top speed your system should be designed for to ensure you always have enough power to stay at your target speed of 51kph over the whole journey (my mention of 60kph+ was a guess).

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Re: more volts better?

Post by amberwolf » Mar 14 2018 1:27pm

If for some reaosn the RPM limiter doesn't do what you're after, then for an automated speed limiter you can use the Cycle Analyst from Grin; if you're not already using one.

flippy wrote:
Mar 14 2018 9:58am
my slight worry is the motor. i do not know how it will like having shoved 80V into basically a 48V motor.
If it's a brushed motor, it'd have extra wear and tear on the brushes and commutator from this, and more waste heat out of the watts poured into it, heating it up more than you'd expect from the higher power level.

If it's brushless, it doesn't care what voltage you put thru it. It only matters the total wattage creating heat vs what it can shed.

There's various calculators to guesstimate what your watts at a specific speed might be, on flat roads. Then you can use a calculator (same one or different) to see what the watts would be at that speed on the worst slopes you have to deal with.

Then you can add in some percentage to deal with headwinds, etc.; whatever you know you'll encounter that will require more power to overcome and maintain the speed you're after.

Once you know what that wattage is, you can then guesstimate if your hubmotor is capable of doing that continuously. If it isn't, there's a number of threads about cooling hubmotors that might fix that; statorade (ferrofluid) and hubsinks are the simplest effective method of shedding heat that doesnt' require opening up the hub, or dealing with leaking oil or other fluids on your tires and brakes, etc.

Then, knowing the wattage its' going to take to maintain that speed, you can work backward thru your controller and battery to be sure they can also handle that kind of power, too. If they can't, you can replace the controller, and add more parallel cells to the battery, or rebuild it with new ones that are higher capability, or both.

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flippy   10 kW

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Re: more volts better?

Post by flippy » Mar 15 2018 4:49am

it's just a standard 1.5kW V2 hub motor. so ferrofluid is the only thing i can do to cool it. there is no space for hub cooling fins. it's not a bike.
Image


i might put in 1 or 2 small fans to circulate the air inside the motor better in order get more heat into the side panels to cool it. but i have to get another 5v supply to drive those, i cant use the output of the controller for this.
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Re: more volts better?

Post by Punx0r » Mar 15 2018 8:33am

Check out some of John's old posts on methods to air cool motors like these with air scopes/vanes

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flippy   10 kW

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Re: more volts better?

Post by flippy » Mar 15 2018 9:50am

Punx0r wrote:
Mar 15 2018 8:33am
Check out some of John's old posts on methods to air cool motors like these with air scopes/vanes
already read those and the motor needs to stay closed. this is a daily workhorse that gets driven in summer, rain and snow. the next battery version will also have internal heating to keep the battery at 20c during cold weather. so i cant have big holes in the motor when it's pissing outside. not to mention the sand and other crud that ends up inside the hub.
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Re: more volts better?

Post by Punx0r » Mar 15 2018 10:32am

Ok fair enough. I wouldn't bother with internal fans to circulate air, you should have reasonable turbulence anyway from the stator spokes and winding end turns churning up the air in the sealed shell. If not, mechanical vanes attached to the stator would be simpler.

Statorade might still help by transferring heat to the wheel rim and using it as a limited cooling surface. Otherwise, there's oil (ATF) fill which would help shed head via the motor side-covers, but it can be a pain to stop oil leaking out of the motor.

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Re: more volts better?

Post by amberwolf » Mar 15 2018 12:55pm

flippy wrote:
Mar 15 2018 4:49am
it's just a standard 1.5kW V2 hub motor. so ferrofluid is the only thing i can do to cool it. there is no space for hub cooling fins. it's not a bike.
If there's clearance on the side covers to the frame, etc., you could bolt heatsinks to those. :)

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Re: more volts better?

Post by John in CR » Mar 15 2018 5:52pm

Mine are daily rider workhorses too. I just opened mine after 5 years of strong air flow, and I couldn't believe how clean the inside was, so anything sucked in blew right out the other side with the exception of a tiny amount of magnetic dust stuck to the magnets. Exhaust holes must extend to the perimeter of the motor to accomplish this. My only concern would be salt if you ride where there's snow, but put a conformal coating on the hall board and hall wires, along with a good coat of electric motor paint on everything, and it would likely be fine. Just rinse with clean water after use. Also, make sure you mount the motor, so the halls and hall boards are high in the motor, not low, to reduce the risk of getting them dunked.

A sealed motor will suck water in through the wires. Take a look at Justin's tests in this regard. There's no way to stop water ingress, so I'd much rather have it open so it dries out. On the intake side I drill the tiniest holes and cut the tiniest slots for air intake. I use straight cuts perpendicular to the axle to avoid any "scooping" action to catch debris. The tire must also play a role in deflecting dust and debris.

I've bought used motors from hardcore commuters, and they were always sealed, and had significant rust from water getting in. There's a large volume of air inside motors like yours, and after getting heated up, it will suck available water in as the air cools and contracts.

Our motors are like alternators with hall sensors. Alternators work for decades open and exposed to the elements.

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Re: more volts better?

Post by Toorbough ULL-Zeveigh » Mar 15 2018 8:50pm

amberwolf wrote:
Mar 15 2018 12:55pm
flippy wrote:
Mar 15 2018 4:49am
it's just a standard 1.5kW V2 hub motor. so ferrofluid is the only thing i can do to cool it. there is no space for hub cooling fins. it's not a bike.
If there's clearance on the side covers to the frame, etc., you could bolt heatsinks to those. :)
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