Controller to run both 36V & 72V ?

[WaterDog]

Hi Guys,

Would a different controller allow, by adding a second 36V battery and the appropriate switches, the bike to run as either: (1) 36V or (2) in series at 72V?

I read a post that I understood as suggesting that my brushless motor can likely handle 72V. This Prodeco Phantom X3 e-bike has an OEM 500W brushless motor in the hub of the rear wheel and was designed for 36V. Various pictures are below.

I'm imagining that I could chose between a long-range 36V slower bicycle or a really fast bicycle shorter-range extra-fun bicycle.

The OEM 36C 16Ah battery has been replaced by a 36V 10Ah battery. Currently it's speed limited to 20mph. I'm turning it into my SUV - local cargo hauler and recreational traveler. I intend to buy a second 36V battery for longer trips. I already have a heavy duty 40A switch so that I can run the second battery after I've used the first.

It's got a twist throttle. It has no LCD display, no sensor for pedaling torque, and no brake sensor. I have ridden motorcycles for decades and am confident without any of that.

The only connections used on the current controller are:

• Two wires (red and black) to battery

• Four wires to twist throttle that has 3 lights to show battery status

• Nine pin connector to the hub motor

If I can use a different controller to run both 36V and 72V, what controller do you suggest?

Thanks!

Joe

(BTW I understand that by adding solder to the shunt, I could increase torque, but probably not top speed.)

 

[amberwolf]

Would a different controller allow, by adding a second 36V battery and the appropriate switches, the bike to run as either: (1) 36V or (2) in series at 72V?

Yes...but:

--The BMS of both batteries has to handle that full 72v (or higher) because if either one shuts down for any reason, then you can end up with the full seriesed pack voltage across just the FETs of that one, and if they can't handle it they fail. The most common failure mode for FETs is shorted, which means that you might not see an immediate problem, but that the BMS can no longer turn off the output so it cant' protect the cells from overdischarge, and you can damage the cells (with the potential risk of fire after the right kind of damage).

--If you put twice as much voltage across the motor, it will try to go twice as fast (at full throttle). If you already get about 20mph out of it, it means that full throttle unloaded would be around 40mph...but air resistance at those speeds wont' let you actually go that fast, and the difference in the actual speed vs the speed it's trying to make you go generates waste power as heat in the motor....potentially damage windings, halls, wiring insulation.

You may also want to test ride down a good hill to see how the bike responds at the faster speeds, if you haven't already. Some of those bikes can get a death wobble going from frame flex, and they don't all have great brakes either.

I read a post that I understood as suggesting that my brushless motor can likely handle 72V.

Yes, it will phsyically handle it fine, as far as the voltage itself goes.

I intend to buy a second 36V battery for longer trips. I already have a heavy duty 40A switch so that I can run the second battery after I've used the first.

If you run them both in parallel, all the time, they'll both last longer and perform better, and you'll get a bit more range out of the whole setup, because there will be less voltage sag under load.

Four wires to twist throttle that has 3 lights to show battery status

If you do series the batteries, you'll probably need to disconnect the fourth (battery voltage) wire, or the doulbed voltage may blow up the electronics in there (depends on the design of the meter). (doesnt' have anything to do with the throttle itself)

If I can use a different controller to run both 36V and 72V, what controller do you suggest?

There's quite a few that would work. Some by Grin Tech http://ebikes.ca (the only ebike-related company I've bought from that I would recommend) include the Phaserunner
https://ebikes.ca/shop/electric-bicycle-parts/controllers/phaserunner-l10.html
and the Grinfineon 72v version.
https://ebikes.ca/shop/electric-bicycle-parts/controllers/c7240-l10.html
https://ebikes.ca/product-info/grin-products/grinfineon.html#FAQontheCurrentSinewaveGrinfineonControllers

You may have to change connectors on various things to plug them into the new controller (either the stuff already on the bike, or the controller's). They carry cables and connectors to match what's on their controllers, if you want to do it that way.

(BTW I understand that by adding solder to the shunt, I could increase torque, but probably not top speed.)

Remember that doing this prevents the controller from knowing what the current actually is, and it can no longer protect itself against overcurrent, so there is a risk of the FETs just blowing up randomly. (usually during higher throttle usage..but not always). It works most of the time, but since the protections are removed, there are failures.

 

[WaterDog]

Wow, Amberwolf, wow!

Thank you for so much thought and specificity. I will be going back to slowly digest your thoughts. But I wanted to immediately let you know that I'm quite grateful for so many things that you alerted me to, such as:

• Death wobbles. I crashed hard as a child from this. And I don't know how my bike handles high speed. I'll check it out using your suggestion to find a hill and safely test this progressively.

• BMS issues. Hadn't considered this.

• Possible damage to motor from air resistance creating heat. I'd love if I could have reliability and speeds up to say ~30mph.
  I'm in Los Angeles and don't have many opportunities to go faster and be within my feelings of what's safe around car drivers.

• I hadn't heard that the batteries would last longer and perform better if run in parallel. Sounds accurate intuitively.

• I had been wondering how the increased voltage might affect the electronics in the battery status lights next to the twist throttle.

• And I appreciate your direct answer with a list of specific controllers

Gratefully,

Joe

 

[WaterDog]

So, the specs on the battery I purchased (36V 10AH Lithium LiFePO4) state that it has a "12S Cell 36v 30A BMS built in the battery pack."

I'd like support and thoughts on Amberwolf's BMS concerns. I have only rudimentary understanding of BMS. I have considered rebuilding the battery pack for two reasons: (1) to change its square-ish brick type shape; and (2) learn more this technology. If I did, I could consider a different BMS.

I'm guessing that: (a) 72V (or higher voltage when charging/fully charged) would likely fry the 36V BMS; and (b) A 72V BMS wouldn't properly manage the charging of a 36V battery pack.

Should I also or instead be focusing on amperage?

Still feeling that gratitude for all the support from Amberwolf!!!

Joe

 

[amberwolf]

• Possible damage to motor from air resistance creating heat. I'd love if I could have reliability and speeds up to say ~30mph.
  I'm in Los Angeles and don't have many opportunities to go faster and be within my feelings of what's safe around car drivers.

depends on the motor and your throttle usage and he speed your trying to go and he conditions, for how mch power is wasteda dn how much heat is generated.

if you go to grin tech's ebikes.ca motor simulator and pick the 9c 2807 i's progbably a lot like your motor. then pick the controller type that you'd probably use for the new setup, and the battery, you mgiht ahve to use a custom to get the voltage. then setup bike wheels size weight and riding conditions and test hrottle positions vs speed to see what happens and watcht he numbers below the chart for heating and power usage etc.

theres also a trip simulator once youset up the bike the way you need in the motor simulator to try out a specific trip.

probably work fine with that motor but don't know it so can't sayh for sure.

 

[amberwolf]

sorry the bleow is all rambly and jumbly and raw, i kept dozing off.

So, the specs on the battery I purchased (36V 10AH Lithium LiFePO4) state that it has a "12S Cell 36v 30A BMS built in the battery pack."

all that means is the bms is made to keep tabs on 12 series cells of lifepo4 chemistry, and that it is made to handle up to 30a output. it might or might not actually limit the output to 30a by shutting off power if you exceed it, it might just only be made to handle that much current.

most stuff doesn't have sufficient info on it's lables or even the seller's ad page to really know mcuh useful info about them, and almost never everything you really need to know ot use it outside it's design intent (whcih is what you want to do).

if you didn't want to use 36v and 72v modes (which isn't really necessary, unless you simply can't control your throttle hand to limit your own speed) then just use a single 72v lifepo4 bms that does 24 cells in series, at 30A max (since you dont' know what the cells can actually handle, safer to assume you shouldn't exceed that) to manage both sets of cells instead of the 36v ones in series.

of course first you can just try it out with both of them in series and if the bmss blow up then you can get the 72v, and if they don't then you are all set.

I have considered rebuilding the battery pack for two reasons: (1) to change its square-ish brick type shape; and (2) learn more this technology. If I did, I could consider a different BMS.

You probably can't chang4e it's shape. it's probably made of flat pouch cells inside that can't be change din layout because it won't have the right pressure on the cells to keep them from swelling up in use.

if it's made of a bunch of cylindrical cells, you could change its shape to some degree, but you should leave the existing tab strips all in place, and just cut the strips between the cells so youc an then solder new interconnects between the tabs, and not solder to the cells or have to buy and learn how to use a spotwelder and all the headache and cost this can entail.

I'm guessing that: (a) 72V (or higher voltage when charging/fully charged) would likely fry the 36V BMS; and (b) A 72V BMS wouldn't properly manage the charging of a 36V battery pack.

the frying depends on the fets used in the bms. you could open the pack and look at them to get the p/n off them and search for the datasheet, then find the Vds figure which is the max voltage they're meant for.

the managing is complex. some bmss can be set for the number of cells they are acutally motniroing, afaik mostly the bluetooth capable ones or the ones that have their own displays or cna be hooked up serially to something for programming and monitoring. so that's not necessarily a problem

but if you have to reconfigure the battery from 36v to 72v you have to stop and turn the bike off. and you also have to disconnect all the balanc wires that were bewteen the 36v packs in parallel, and the main wires, and the bms, and then you have to reconnect all taht stuff so the packs are in seires and connected to the bms correclty. then you have to change the bms settings so it is now monitoring as 72v,, then you have to turn it all back on and start riding again. hen you have to do taht all in reverse to go back to 36v

so what i would do instead is just make a 72v pack out of the two 36s, or just buy a 72v that can handle the current draw you need for your riding conditions, and has the ah you need for the range you want.

then use a 72v controller, and just manage your throttle hand to keep your speed wher eyou want it.

if you can't then you can get a controller that has programmable levels and then set them up to the speed ranges or whatever that you want, and siwtch between them as needed.

or if you can't get that contorller or want something simpler, add a switch to your throttle that puts a voltage divider on the signal line to cut the voltage output in half, or something similar.

Should I also or instead be focusing on amperage?

current matters because your bms is limtied to 30a either to protect the cells or to protect the bms. or both.

30a may actually be a peak current rather than constant, becuase most of these lifepo4 cells can only really handle 2c at best and if its 10ah thats only 20a. Some fo them only take 1c or 10a without lots of voltage sag / etc.

So 30a is 3c (3 x 10ah) and you might get so much voltage sag at tah current level that it causes problems, especially as the battery is more emtpy than full, either bms shutdown due to cell level lvc or controller shutodwn due to battery level lvc (assuming you dont[' use something that can do donw to 36v vbut is only meant for 72v). Or the cells will just be pushed so muich harder than they were meant for that they age faster than usual, heat up more, and start losing capacity/etc faster than normal.

But without knowing exactly which cell is in there and exactly what those cells are actually capapble of from the manufacturer (not from the seller, who will often lie outright to make a sale, so i don't trust what any of them say, and the cheaper it is the less likely it is that what they say is real), real world testing is the only way to know what they'll really take.