Undervolting question

[charlesv842]

Is it safe to run 24 volts through a 36 volt system? What about controller?

 

[dogman dan]

likely won't work, because the controller will hit it's low voltage cut off. But some early systems could run 24-48v, notably the Aotema stuff sold by Wilderness Energy.

Would work with a 24v controller, but be at least 5 mph slower, or more.

 

[charlesv842]

Would that setup be slower than or the same as a 24 volt system and 24 volt motor?

 

[Simonvtr]

Hi Charles

Are you doing this on your e scooter? reading your past post the controller was designed for 24v? unless you have changed the controller?
I had a dc to scooter controller that was rated for 24 and 48 volts, caps on the controllers was rated for 60v.
I did not notice these cheap dc controller having a cutoff when I was using them, unless there is documents that says they have a lvc then you can run 24v even tho the controller is rated for 36v. Might want to look up the model of your controller and see what the specs are. When it comes to running 36v vs 24v on the same setup the huge change will be the amp draw of the controller. Lets say 36v battery with a brush motor spinning at 2500 rpm will pull 18amps from the battery, now same setup but you reduce the battery to 24v the same motor will pull 28amps to reach the same 2500rpm. What makes this important is the more amps that you have running thru the wires/system the more heat you will generate. So it is important to make sure the battery and motor wires are the correct gauge. And as dogman pointed out you will notice a drop in speed/torque to the system.

 

[charlesv842]

This is actually for a bicycle hub motor. I'm looking into buying a front wheel kit. I would like to get a 24 volt system because I want to use SLAs and I only want two. But I haven't found very many of them for a low price, especially because shipping is high because a lot of what I have found is coming from overseas. But 36 volt kits seem to be cheap and plentiful. That's why I'm looking at those, but running 24 volts. Plus I can always upgrade the voltage and controller later if I want.

So what you're telling me is running 24 volts with 24 volt controller in a 36 volt motor will pull more current and be a little slow?

 

[999zip999]

Where do you live ? 24v is slower then 36v. Volts is speed.

 

[dogman dan]

Without changing the motor, you will have a maximum no load rpm on 24v that is slower than the no load speed at 36v. It really is that simple, the motor will spin slower on lower voltage.

This is what your controller does btw. by pulsing the power on and off, it tricks the motor into thinking its getting lower voltage. At WOT, no pulsing, and full rpm.

 

[slcpunk]

probably should start a new thread, but hoping maybe this will be found here...

maybe similar question ( and all my reading hasn't made it clear )

I have a voilamart rear hub motor kit. specd 1000w 48v with a 48v battery pack. the SW900 controller has a setting for voltage - can I use that to set it to 36V and get lower power and maybe longer battery life? the thing is so powerful, I really want to slow it down!

I can't find much info on the controller - sort of a generic silver box without much data.

most appreciative...

 

[donn]

No, that's why it really isn't a similar question - your battery is 48V, so that's the system voltage. The actually voltage to the hub is controlled by some kind of throttle. If it's built into the cranks ("pedal assist") and there isn't a workable way to get it to work the way you want, there may be a way to add an inexpensive throttle.

 

[Drunkskunk]

........ the SW900 controller has a setting for voltage - can I use that to set it to 36V and get lower power and maybe longer battery life? the thing is so powerful, I really want to slow it down!.....

Nope. setting the controller for 36v will only reset the low voltage cutoff from 40-ish volts to 30 volts. Doing that with a 48 volt battery is a good way to destroy it.

Instead, you can set the power with that SW900. If you're on pedal assist, and already on PAS 1, you can set the PAS sensitivity and the PAS start strength lower.You can also set your magnet type. If this setting is accurate, then a higher count will make the controller think you are pedaling slower.

If you're using the throttle, you can set the current limiting lower. I think default is 12a, which is very low. The range is 1 to 20a.
Instructions can be found here:
LCD-SW900 INSTRUCTIONS

 

[MadRhino]

Motors are not voltage specific, nor wattage for what matters. They spec voltage as a system component, usually with the speed it would achieve at that voltage. Wattage spec is normally the continuous power that a motor can tolerate, but sometimes only a reference to system setting/capability. The motor in a 500w kit is often the same as in a 1000w kit, then the wattage is only about system setting. Many 1000w DD hub motors can be fed 10kw for a few seconds in acceleration without any damage, and the motor from a 36v kit could be fed 100v safely. Well, safely for the motor I mean. We feed it thousands of volts when testing winding insulation. On the low side, a motor can be fed as low voltage as to make it spin, with the condition that more Amps will be required at lower voltage to achieve equal watts.

 

[MadRhino]

Feeding different power and voltage is only a matter of battery capability and controller setting.

Lead is dead. We don’t use SLA anymore for ebikes, for there are too many downsides to them. Even the cheapest Lithium cells sold by the pound at recycling centers, are much better than lead.

 

[dogman dan]

2 12 ah lead will only be suitable for very short rides. You will wreck lead batteries very fast if you discharge them more than half way. So 6 ah x 24v gets you only 150 watt hours. Enough for about 6 miles max, round trip. But soon you will have only 4 ah to half, then 3, and so on as the lead quickly ages. It would be worth it to carry three, so you could ride more than 4 miles round trip.


24v brushless bike motor controllers will be hard to find. Typically they start at 36v for bikes. Another good reason to go 36v.

 

[slcpunk]

........ the SW900 controller has a setting for voltage - can I use that to set it to 36V and get lower power and maybe longer battery life? the thing is so powerful, I really want to slow it down!.....

Nope. setting the controller for 36v will only reset the low voltage cutoff from 40-ish volts to 30 volts. Doing that with a 48 volt battery is a good way to destroy it.

Instead, you can set the power with that SW900. If you're on pedal assist, and already on PAS 1, you can set the PAS sensitivity and the PAS start strength lower.You can also set your magnet type. If this setting is accurate, then a higher count will make the controller think you are pedaling slower.

If you're using the throttle, you can set the current limiting lower. I think default is 12a, which is very low. The range is 1 to 20a.
Instructions can be found here:
LCD-SW900 INSTRUCTIONS

Thanks so much - Unfortunately, I had already done all of the things you suggested. I'm glad I didn't change the voltage - sort of guessed that was a bad idea!

Pas 1, pas sensitivity low, start strength and magnet count. Unfortunately they didn't have much impact - with a magnet count of 12, i found that if i pedaled backwards, it would be confused and still apply power!

I didn't hook up the throttle, but I may since it seems that would be a way to control it. Everything I've observed seems to tell me that with PAS you get full power up to a speed limit ( VS less power output for slower acceleration ).

Thanks again, appreciate the explanation.

 

[slcpunk]

What affect does the "current limiting" option have?
I think the range on the SW900 is 12-20, and the controller I have says "26A +/- 1"
Thanks again