Voltage query

[Fordulike]

After somebody on another thread mentioned Conhis motor, i took a look at their website.
Now i thought i had grasped the basics of battery power and motor power, but something has stumped me.
They sell a 24v 200w motor and also a 48v 200w motor.
Now i was under the impression that the motor takes the power it needs.
If it's rated at 200w, ignoring peaks, it would provide an average of 200 watts of power.
I assumed that the higher voltage motors would by default have a higher wattage rating.
Would the 48v motor have more torque or spin quicker?
Please can someone explain as my head hurts

 

[Fordulike]

Have i explained properly or is it gobbledegook?

 

[NRG]

The stated wattage is the continuous power rating of the motor. In use the power will peak and dip depending on load and throttle position. The higher the continuous rated power of the motor the more the power will peak depending on the ability of the controller to supply the current.

With regard to voltage the motor coils will be wound with a specific voltage in mind to meet the electrical design criteria and speed for a given wheel size so a 24v 200w motor sized for a 26" wheel to give a speed of 15mph or so will be wound for an RPM of 193 or thereabouts. The same wheel but with 48v motor would be wound to meet the same RPM but the difference is the amount of current used to get that speed, halving the voltage doubles the current draw....doubling the voltage halves the current draw. So 200w / 24v = 8.33amp, 200w / 48v = 4.16amp or half....

Either way you cut it the power will be the same. The main difference though will be the dictated size of the battery due to the current draw. A 24v motor with a 24v battery will need more Ah to get the same Wh rating as a 48v battery IE: A 48v 10Ah battery has a Wh of 480, to get the same for a 24v battery you would need a 20Ah battery.

Over volting a motor will make it spin faster so you can get more speed but the constraint will be the controller maximum voltage and the extra generated heat inside the motor, you can only go so far

 

[Fordulike]

Quote:
Either way you cut it the power will be the same. The main difference though will be the dictated size of the battery due to the current draw. A 24v motor with a 24v battery will need more Ah to get the same Wh rating as a 48v battery IE: A 48v 10Ah battery has a Wh of 480, to get the same for a 24v battery you would need a 20Ah battery.

After looking on Ping's website, the two different batteries are roughly the same price and physical size.
If the outcome is the same whichever voltage one opts for, i still don't get why someone would choose one over another

 

[jerrysimon]

Well from my basic understanding you would choose the higher voltage option for less current draw for the same power.

Advantages

1. For lower current draw the cable could be thinner ?
2. The motor would run cooler for the same speed ?

I also thought a higher voltage motor spins faster for the same amount of current draw, as a smaller voltage motor ?

As I said I am no expert lol

PS just re-read my reply I think its probably pants

Regards

Jerry

 

[flecc]

It is fundamentally about wire thickness. As NRG says, the higher the voltage the lower the current for a given power, and the wire thickness to carry current depends only on the current in Amps, not the volts. That's why fuses are rated in Amps, not volts.

For example, the cables that electricity pylons support feed electricity to many thousands of homes and businesses, each using many Amps. If the power was being sent at 220 volts, the cables would have to be many feet thick to carry the many thousands of amps which wouldn't be possible. The cables would break under their own weight or the pylons would collapse.

Therefore the power is sent at very high voltage which reduces the number of amps pro rata. At 22,000 volts the cables could have only 100th of the cross section, at 220,000 volts, 1000th of the cross section.

In motor design, it's a matter of balancing the factors for the desired result, and for e-bikes about 24 to 36 volts is generally preferred to provide for the legal market. Those Conhis motors often provide for the UK illegal market, and for those higher powers, higher voltages can be more suitable.

In a motor example, to double the power of a 24 volt 200 watt motor to 400 watts, there's two simple ways:

Double the cross section of the wire in the motor coils to enable double the amps to flow. This would increase the motor weight and size, but keep running temperature roughly the same.

Double the voltage of the existing motor, keeping the Amps the same. This would keep the motor small but increase the running temperature considerably.

The designer chooses the compromise best suited for the purpose.
.

 

[Old Timer]

Tony

what I was surprised at was the thinness of the wires from hub to controller on Annes Brushed 36V synergie.

Going on from that, I took two Kettle plug leads (the type you might use as an extension being male one end and female the other.) I needed to make up two patch leads to be able to use a variety of batteries with any of our bikes. The leads were 12" long, I cut them in the middle and made up a lead male+male and a female+female. The quality of the cables were nothing special and not up to running a kettle so they were obviously designed for pc work or similar. Anyway, I soldered the wires and then heat shrunk them.
I tried them out yesterday for some 6 miles or so with the synergie 36V battery running my 36V powertrek( a heavy bike made even heavier with the two batteries on board) via one of these patch leads and it ran perfectly powerfully and absolutely no warming of the cable or plugs. Now if i look at the normal default cables from the powertrek or my Alien the cables are of much thicker diameter. Are the manufacturers erring on the safe side or might I get a problem if running the bikes for a further distance (ambient temp yesterday was around 15 C.)

 

[flecc]

Since the cables didn't get warmer Dave, you shouldn't get any problem, even when the weather warms up more. The first effect of cables too thin is a loss of power and some warming, the two going together, more loss of power = more warming. If you noticed no power loss, it will be ok.
.

 

[Fordulike]

Thank you for all of your knowledgeable replies.
I've now got my head around the topic and i should imagine the thread has helped others too

 

[Old Timer]

Since the cables didn't get warmer Dave, you shouldn't get any problem, even when the weather warms up more. The first effect of cables too thin is a loss of power and some warming, the two going together, more loss of power = more warming. If you noticed no power loss, it will be ok.
.

Thanks Tony

What is your view re the thin wires on the synergie brushed motor, does a brushed motor require less heavy duty wires would you think?

 

[flecc]

Not for a given voltage and power output since the amperage will be the same, though at a guess the brush impedance may give a slower rise time in the current pulses. That wouldn't make much difference to wire thickness requirement though.
.

 

[piotrmacheta]

Given all this current/voltage relationship could I run an ezee motor at 72 volts if I kept the current low (say 15 amps)? Anybody with any experience?
I run my hub at 37V with a 300rpm hub on a 20" wheel and this gives the normal 15 to 17mph speed and about 15 amps and I tried it at 48V and got 20mph ish and the current peaked at 22 amps.

 

[NRG]

Well you could but I'm not sure how long it would last Things to consider if planning to overvolt a motor...heat build up could be a problem when climbing hills if the motor is allowed to slow too much, so, the faster the better up hills is best....the hall effect sensors if fitted can fail...the controller will have an upper maximum voltage limit many are around 50~60v so you're probably going to need a new controller and a new throttle to go with it...a new controller designed for the voltage will give correct low voltage cutoff protection for the battery... Any lights driven from the battery may now need an independent battery...your bike is now illegal!

 

[Dynamic Position]

Tony

what I was surprised at was the thinness of the wires from hub to controller on Annes Brushed 36V synergie.

Going on from that, I took two Kettle plug leads (the type you might use as an extension being male one end and female the other.) I needed to make up two patch leads to be able to use a variety of batteries with any of our bikes. The leads were 12" long, I cut them in the middle and made up a lead male+male and a female+female. The quality of the cables were nothing special and not up to running a kettle so they were obviously designed for pc work or similar. Anyway, I soldered the wires and then heat shrunk them.
I tried them out yesterday for some 6 miles or so with the synergie 36V battery running my 36V powertrek( a heavy bike made even heavier with the two batteries on board) via one of these patch leads and it ran perfectly powerfully and absolutely no warming of the cable or plugs. Now if i look at the normal default cables from the powertrek or my Alien the cables are of much thicker diameter. Are the manufacturers erring on the safe side or might I get a problem if running the bikes for a further distance (ambient temp yesterday was around 15 C.)

The wires from the hub to the controller on Anne's bike may be protected by a fuse? If this is so a smaller C.S.A. wire would be acceptable. The thinner wire having the advantage of increase in flexibility and visually less intrusive and lighter - parameters advantageous in e-bikes.

Your male+male patch lead presents a problem with potentially exposed conductors which could present the risk of getting an electric shock.

 

[Old Timer]

The wires from the hub to the controller on Anne's bike may be protected by a fuse? If this is so a smaller C.S.A. wire would be acceptable. The thinner wire having the advantage of increase in flexibility and visually less intrusive and lighter - parameters advantageous in e-bikes.

Your male+male patch lead presents a problem with potentially exposed conductors which could present the risk of getting an electric shock.

good point, I`ll be careful

 

[clckn2000]

I don't know about other forum memebers but I think the 15 mph restriction is too low. In normal traffic conditions it would be safer to be able to reach 20 befor the power cuts out. Also, should the power delivery be higher. I don't understand the technology numbers but a 350 watt motor would be a better maximum which i assume would give better hill climbing capability.

 

[flecc]

I don't know about other forum memebers but I think the 15 mph restriction is too low. In normal traffic conditions it would be safer to be able to reach 20 befor the power cuts out. Also, should the power delivery be higher. I don't understand the technology numbers but a 350 watt motor would be a better maximum which i assume would give better hill climbing capability.

These are quite widely held views, and both higher speeds and more power are available in some EU countries in a different class of e-bike and in theory could be in other EU countries as well. However, these faster/more powerful classes have more restrictions like registration, number plates and compulsory insurance etc. Most wouldn't welcome that.

The basis of the law as it stands is that e-bikes should remain with the common speeds of normal utility bikes, typically up to 15 mph, not the 20 mph of outright sports bikes as ridden by the very fit. However, BEBA is attempting to get agreement on higher powers like 350 watts to improve hill climbing and be more useful to partially disabled riders.
.

 

[jkirkebo]

Well you could but I'm not sure how long it would last Things to consider if planning to overvolt a motor...heat build up could be a problem when climbing hills if the motor is allowed to slow too much, so, the faster the better up hills is best....the hall effect sensors if fitted can fail...the controller will have an upper maximum voltage limit many are around 50~60v so you're probably going to need a new controller and a new throttle to go with it...a new controller designed for the voltage will give correct low voltage cutoff protection for the battery... Any lights driven from the battery may now need an independent battery...your bike is now illegal!

Yeah, the motor would probably not work long at 72V. 48V is the max I would try, and one needs a new controller for that. I run a modified US version Ezee controller at 44.2V (7.2V booster pack) on 26" wheels and cruise at around 22mph though I still get 200W of assistance at 25mph. 800W peak power on fresh batteries.

 

[clckn2000]

Thank you for the clarification. If the BEBA is successful, many currently compliant bikes will be out of date. I wonder if after maket companies will emerge with conversions for 350 motor systems. Would this change require a change to the battery output or controller characteristics?

 

[aussiejeff]

Yeah, the motor would probably not work long at 72V. 48V is the max I would try, and one needs a new controller for that. I run a modified US version Ezee controller at 44.2V (7.2V booster pack) on 26" wheels and cruise at around 22mph though I still get 200W of assistance at 25mph. 800W peak power on fresh batteries.

Hi jkirkebo.

I have also modded my 26" MTB with a similar voltage boost as yours.

Original system purchased from EVS in Melbourne, Australia was a 200W 37V Bafang brushless motor with an Ananda controller rated at 15Amps. The kit came with a Phylion 37V 10AH battery.

Initially, for the first few months I was wrapped in the extra speed & distances I could cover on country road trips with the freewheel pedal assist (I'm almost 60 and my distance ability due to bad back & deteriorating knees had been steadily declining over the past couple of years).

I DID start to wish for a few more kph of assist, though, as I had discovered the best average speed I could sustain on the flat (no wind) with WOT plus moderate pedalling was around 26kph. Up smallish hills with around 3 degrees slope I could manage around 22kph with a bit heavier pedalling - but not for any long climbs - back to about 18kph sustained then (pulling the max pack watts of 530-540W). Since reading threads here and in the Endless-Sphere forum I worked up the courage to add a 7.2V "booster" pack in series as well.

Soooo.... I had 5 R/C NimH packs still in pretty good nick (rated at 7.2V 3700mah) sitting around doing nada since I quit the local R/C club scene. I took the batts out of mothballs and they all charged up to between 8.4-8.5V. Looking good! Then I made the individual packs up into a single cable tie, packing foam & gaffer tape bound "boost pack" with a potential capacity of 18.5AH.

A quick bit of history here. Just prior to this "experiment", I had also purchased a Headway 36V 10AH pack & a "cheap" replacement 37V 14AH Lipo from EVS (at 50% cost to replace the original Phylion, which I & they had presumed stuffed when it began rapidly losing capacity - I subsequently stripped the battery after they sent it back and discovered the BMS plug had come loose - thus the cells all unbalanced! Hmmmm, methinks. So, I re-seated the plug, manually re-balanced each cell to within .05V each - which took ages - then recharged and tested the battery - VOILA! - 90% capacity restored and getting better each ride!).

Thus, the current battery "zoo" I have consists of:

1 x 37V 10AH 2C rated & repaired Phylion
1 x 37V 10AH 10C rated LiFePO4 Headway
1 x 37V 14AH 3C rated Lipo
1 x 7.2V 18AH 1C rated NimH booster

The Headway pack after charging and fitting gives me around 42.5V. The booster pack gives around 8.5V after fitting to the special battery rack I had made to go on the front frame where the drink bottle usually sits.

My Cycle Analyst shows on ave this combo gives me around 51.0V at start of ride. After about 1km of mostly flat riding, the surface charges have worked down to settle around 48V total - enough to get me along with assist all the way up to 35kph which is a very comfortable speed for me to pedal assist at!

For example, my last ride stats with that combo -

Pack start = 50.9V (Headway 42.6V, Booster 8.3V)
Pack Finish = 47.1V (after 5 mins rest - Headway 39.4V, Booster 7.7V)
Est % Headway "Useable" volts used = 29.5%
Est % Booster "Useable" volts used = 22.7%

Trip Dist = 29.7km
Ave Speed = 29.5kph (mainly flat with a few medium hills)
*NOTE*Previous BEST Ave Speed This Course With 36V = 26.0kphTotal A/Hours used = 5.65
W/Hours used = 260
WH/Km = 8.7
A/Max = 15.7
V/Min = 39.4
Max Watts Pulled = 720 (33% more than stock 36V setup!)

I must say, riding now is sooo much more pleasurable . The speed I can now maintain on the flat on average with mild pedalling is around 32kph for most of a ride between distances of 30-60km.

The motor and controller temps (with the limited max current of 15.5A offered by the small controller) are only slightly warmer uphill than running stock 36V - though I will consciously limit the watts in hot weather just to be safe!

Thanks to all who set me on the path to "upgrading" the capability of my e-bike!

Somewhere down the track I am thinking of getting a Kelly controller so I can run my setup at a constant 48V with 18A max available for short bursts up hills. I believe I could serial two 37V batts for this purpose, as the 48V Kelly is rated up to 90V input with adjustable V/A output within limits.

Also, I have read most modders who have tried overvolting the low watt Bafang brushless motors seem to think short bursts up to 1000KW are ok in suitable conditions - so I am hoping my theoretical max of 864W with the Kelly setup should be ok .

However, cost of the Kelly 48V controller will be about $200AUS, so have to save some pennies first!

In the meantime, the 7.2V booster is just the ticket.

Cheers,

aj