Adding capacitors for long battery wires

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Hummina Shadeeba   10 MW

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Adding capacitors for long battery wires

Post by Hummina Shadeeba » Feb 23 2020 2:15pm

I searched adding+capacitors. Searching rarely gets me anywhere

For long battery wires what kind of capacitors and how much per foot of 12awg battery wire?

john61ct   100 GW

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Re: Adding capacitors for long battery wires

Post by john61ct » Feb 23 2020 2:24pm

for what purpose?

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spinningmagnets   100 GW

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Re: Adding capacitors for long battery wires

Post by spinningmagnets » Feb 23 2020 5:10pm

If there is a significant distance between the battery and the motor, it is MUCH better for the controller to be as close as possible to the battery, with the three motor phase wires being the longer section. In an effort to reduce voltage ripple and voltage spikes that result from being forced to have longer battery wires, it is sometimes helpful to add capacitors to the red/black pos/neg right next to the controller.

This is because the motor can absorb quite a bit of voltage ripple and voltage spikes, but the controller is much more sensitive. The key metric is to use Capacitors with a low-ESR. A physically larger capacitor with high capacitance doesn't hurt, but it also doesn't help either. A capacitor has two leads, positive and negative. Simply connect the two leads to the two battery cables, in a place near the controller.

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flat tire   1 MW

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Re: Adding capacitors for long battery wires

Post by flat tire » Feb 23 2020 5:13pm

Increasing pwm frequency will also reduce ripple. Danger in long battery wires is also sort of overstated. Most reasonable lengths add really minimal inductance.

Hummina Shadeeba   10 MW

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Re: Adding capacitors for long battery wires

Post by Hummina Shadeeba » Feb 23 2020 11:55pm

For someone’s street luge with skate hub motors.

Extending battery wires seems the easier way.

When u say increasing pwm signal on the motor side of the esc reduces the ripple on battery side, saying one side effects the other, I guess the motor inductance/kv would be a factor too? never heard one side effecting the other I thought was just the inductance of the battery wires slamming some component with a voltage spike when disconnecting was what the caps were for. ripple on the battery side seems to have a negligible detriment to lithium cells. Should I care about ripple on the battery side?

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Toorbough ULL-Zeveigh   100 MW

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Re: Adding capacitors for long battery wires

Post by Toorbough ULL-Zeveigh » Feb 25 2020 5:55pm

Hummina Shadeeba wrote:
Feb 23 2020 2:15pm
I searched adding+capacitors. Searching rarely gets me anywhere

For long battery wires what kind of capacitors and how much per foot of 12awg battery wire?
confine yer search to Lukeforphysics for anything power related as that's his bailiwiki.
then spin-off from there.
search.php?keywords=esl&terms=all&autho ... mit=Search

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flippy   1 MW

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Re: Adding capacitors for long battery wires

Post by flippy » Mar 06 2020 10:42am

unless you have a 30ft long bike you dont need to worry about this. your controller will have plenty of input caps to absorb any issues.
Lithium beats liquid dinosaurs.

Hummina Shadeeba   10 MW

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Re: Adding capacitors for long battery wires

Post by Hummina Shadeeba » Mar 06 2020 1:29pm

Found it:

https://www.rcgroups.com/forums/showthr ... orkarounds

https://www.rcgroups.com/forums/showthr ... st24486468


Flippy I think you’re trying to blow me up! But it’s a street luge n longer than a bike.

JackFlorey   10 kW

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Re: Adding capacitors for long battery wires

Post by JackFlorey » Mar 06 2020 1:57pm

spinningmagnets wrote:
Feb 23 2020 5:10pm
This is because the motor can absorb quite a bit of voltage ripple and voltage spikes, but the controller is much more sensitive.
Agreed. I would also add that a motor winding is, from the controller's perspective, a great big inductor. And making the controller->motor wiring longer just adds a bit more inductance; unnoticeable with the large inductance already present.
For long battery wires what kind of capacitors and how much per foot of 12awg battery wire?
More important to route the wires right next to each other; avoid large loops that can cause more inductance. Also take care that you don't create an LC resonance by pairing the wire inductance with new capacitance. With long enough wires and high quality/low value capacitors, you could create a resonance at the switching frequency that would actually amplify the noise at that frequency. Fortunately the values rarely line up to cause that. Also electrolytic caps are low enough Q that it generally doesn't happen with electrolytics.

Hummina Shadeeba   10 MW

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Re: Adding capacitors for long battery wires

Post by Hummina Shadeeba » Mar 06 2020 2:16pm

I read cells create large capacitance due to their construction.

Punx0r   100 GW

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Re: Adding capacitors for long battery wires

Post by Punx0r » Mar 06 2020 2:39pm

They do, but your cells are not at risk - it's the controller out there on the other end of the wires on it's lonesome. That's why any caps have to be as close to the controller as possible.

Hummina Shadeeba   10 MW

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Re: Adding capacitors for long battery wires

Post by Hummina Shadeeba » Mar 06 2020 2:45pm

Actually I read cells benefit from less ripple but yea the point is mainly to protect the esc and keep it cooler besides

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flippy   1 MW

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Re: Adding capacitors for long battery wires

Post by flippy » Mar 06 2020 5:19pm

Hummina Shadeeba wrote:
Mar 06 2020 1:29pm
Flippy I think you’re trying to blow me up! But it’s a street luge n longer than a bike.
then dont worry about this. unless you have a really shitty controller, then upgrading the crappy caps inside it will yield better results.

dont confuse the controllers we use with drone esc's.
Lithium beats liquid dinosaurs.

Hummina Shadeeba   10 MW

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Re: Adding capacitors for long battery wires

Post by Hummina Shadeeba » Mar 06 2020 6:11pm

What’s difference? Drone or whatever seem to need an amount of caps per wire length and subsequent inductance.

john61ct   100 GW

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Re: Adding capacitors for long battery wires

Post by john61ct » Mar 06 2020 7:51pm

Hundreds of thousands of users fly every day having no idea what capacitance even is.

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flippy   1 MW

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Re: Adding capacitors for long battery wires

Post by flippy » Mar 07 2020 5:03am

Hummina Shadeeba wrote:
Mar 06 2020 6:11pm
What’s difference? Drone or whatever seem to need an amount of caps per wire length and subsequent inductance.
drones run with sensorless controllers that do 30k rippems. then you need to worry about interference.
a simple sub 1000rpm sensored bldc motor doe not generate anything close to the interference that a drone esc has to deal with.

you are comparing a 25k rpm 2 stroke moped engine to a 1200rpm 16 liter diesel truck engine.

drone esc problems do not exist in the realm of ebikes or bigger because they are wildly different. the only thing they have in common is that they turn a shaft.
Lithium beats liquid dinosaurs.

Punx0r   100 GW

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Re: Adding capacitors for long battery wires

Post by Punx0r » Mar 07 2020 5:56am

Ebike style controllers already have plenty of onboard capacitors. It's the smaller, RC style controllers that don't

Hummina Shadeeba   10 MW

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Re: Adding capacitors for long battery wires

Post by Hummina Shadeeba » Mar 07 2020 12:04pm

Drone and bike esc don’t seem so different. Seems mainly need current limiting
viewtopic.php?f=2&t=23882&start=25



I don’t know why u mention interference flippy. I was thinking the caps are for the battery wire inductance so as not to blow up bits in the esc. Actually this street luge is more like twice as long as a bike and with 4 or 6 motors it’s a lot of wires

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spinningmagnets   100 GW

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Re: Adding capacitors for long battery wires

Post by spinningmagnets » Mar 07 2020 12:17pm

Fat wire and capacitors are cheap. Better to add "too many" capacitors to protect the ESC, rather than risk blowing-up a tiny $200 Castle Creations ESC...

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flippy   1 MW

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Re: Adding capacitors for long battery wires

Post by flippy » Mar 07 2020 2:36pm

Hummina Shadeeba wrote:
Mar 07 2020 12:04pm
Drone and bike esc don’t seem so different. Seems mainly need current limiting
viewtopic.php?f=2&t=23882&start=25
I don’t know why u mention interference flippy. I was thinking the caps are for the battery wire inductance so as not to blow up bits in the esc. Actually this street luge is more like twice as long as a bike and with 4 or 6 motors it’s a lot of wires
current limiting is not what they do. they convert DC into 3 phase AC.
they both do the same job, make a motor turn. but comparing them is simply not fair to the drone esc. and with interferance i mean inductance if that is what you are concerned about. there are many more issues when you go down the rabbit hole.

but fact remains that these issues you see with drones is simply not applicable to bike or scooter controllers.
a 4kW hub motor shipped from QS has 5ft of wires, that is 15ft total just for the motor phase wires. i rebuilt a couple golf carts with nearly 10ft of wire between the battery and the controllers and 8ft between the controllers and motors. never had a issue.

if your wires are the proper gauge for their job and you have anything else then some shitty aliexpress controller then you will be fine and you can ignore this whole issue, because its simply not a issue. at least not for the stuff discussed there and what you are going to build.

do not bring drone esc "knowledge" to a e-bike build. they are NOT the same thing. a drone esc is built for size and weight, not actual performance. they trim off stuff like proper input capacitance for weight savings. in a bike controller this is not a issue and you have LOTS of input caps as there is no weight or size constraints like you have on a drone.

you want to have some fun: put a drone esc with a simmilar rating as a bike controller on a ebike and run it. see how far it gets you before it burns out.
Lithium beats liquid dinosaurs.

Hummina Shadeeba   10 MW

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Re: Adding capacitors for long battery wires

Post by Hummina Shadeeba » Mar 07 2020 3:07pm

You want to have some fun: add a limit to the current as done by the people in the link I posted

john61ct   100 GW

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Re: Adding capacitors for long battery wires

Post by john61ct » Mar 07 2020 4:54pm

Most of that is a decade old.

And I don't understand how it relates to the topic at hand.

Maybe if you spec your setup, link to components, describe specifically what you are trying to accomplish the community can better advise you.

Hummina Shadeeba   10 MW

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Re: Adding capacitors for long battery wires

Post by Hummina Shadeeba » Mar 07 2020 5:34pm

I was looking for how long battery wires can be before inductance is a risk. The link I posted seems a good source of info related to that and i trust Ron’s info over there on rcgroups.

The luge isn’t mine and posting here to help him get it going and not blow up. Don’t know what version of the vesc specifically he’s using. But I don’t think I need any help thanks and the link I found has all the related info could need

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Re: Adding capacitors for long battery wires

Post by john61ct » Mar 07 2020 6:09pm

Ron?


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