small ebike controllers

[RichardT]

Hello Experts

I bought a mountain bike type of ebike having a panetary-geared brushless hub motor rated at 36v 350w.

The controller is like a big match box. Very small, I estimate it is like 10 cm by 6cm.

When i first rode it on a hot afternoon, after 2 km, the controller casing felt hot.
I rode over short slopes of about 10 degrees gradient for a short distance only and did not throttle all the way with some manual peddling. No pedal assist installed.

I like to know about small sized controllers:

1. Does it mean they are less powerful in terms of amount of amperage it can handle? Well, the label on it says it can handle over 350w based on the 36v x max amp draw, but thats just a labeling. And its a china controller.
2. Is it wise to install a small fan to it by making the casing larger?
3. Are controllers supposed to feel hot? If so what temperature is regarded as too hot ?

Thank you very much for reading my post.

Have a nice day.

Best regards
Richard T

 

[Ralith]

My Castle Creations controller is smaller than that and handles upwards of 2kW continuous. That's high end US-manufactured equipment, but it's certainly possible for a high-power controller to be compact.

It's normal for a controller to get hot if you're using it at the upper end of its power range. "Too hot" depends on the controller; you'll need to find that info from the manufacturer. I'd be concerned if it's too hot to touch.

 

[d8veh]

Generally, the bigger the controller, the more power it can handle, but don't get a bigger controller unless there's a way to regulate the current to what your motor and battery can handle because bigger controllers generally allow more current.

Show us a photo of your motor and tell us what battery you have, and we should be able to advise you what you can do.

Controllers often run warm, but they shouldn't be so hot that you can't hold it against your skin.

 

[sonnetg]

Most small controllers I have used have only 3 FETs. The bigger ones' have at least 6 FETs and more. Bigger controllers can push more Amps and not heat up as much. It should not matter whether you motor can handle the current or not. The motor will simply consume the current it needs, no more..no less. If the controller is smaller, the motor will squeez the controllers harder for more current, hence the controller heats up more...at least thats what I observed.

 

[Hillhater]

I have a small...credit card...sized 3 FET controller rated at 24v, 250W.
But for 5+ years it's been happy to output 30amps on 40 volts without getting hot or showing any signs of stress. ,!

 

[motomech]

This poster is double posting;
https://endless-sphere.com/forums/viewtopic.php?f=35&t=58281&p=874848#p874848
I near as I can tell, he has some sort of pre-built w/ a 24V Lead battery.

 

[d8veh]

Most small controllers I have used have only 3 FETs. The bigger ones' have at least 6 FETs and more. Bigger controllers can push more Amps and not heat up as much. It should not matter whether you motor can handle the current or not. The motor will simply consume the current it needs, no more..no less. If the controller is smaller, the motor will squeez the controllers harder for more current, hence the controller heats up more...at least thats what I observed.

Did you look inside, or are you going by the three fixing screws that you can see on the outside? Are you talking about ebike controllers?

 

[RichardT]

This poster is double posting;
https://endless-sphere.com/forums/viewtopic.php?f=35&t=58281&p=874848#p874848
I near as I can tell, he has some sort of pre-built w/ a 24V Lead battery.

Hey bro,
that was my old controller and old motor kit which i never used due to product issues.

This post is not double posting. Hope there is no misunderstanding.

Thank you.

Regards
Richard T

 

[RichardT]

Most small controllers I have used have only 3 FETs. The bigger ones' have at least 6 FETs and more. Bigger controllers can push more Amps and not heat up as much. It should not matter whether you motor can handle the current or not. The motor will simply consume the current it needs, no more..no less. If the controller is smaller, the motor will squeez the controllers harder for more current, hence the controller heats up more...at least thats what I observed.

This controller of mine has 3 screws shown on the outside of the controller casing. So, i think only has 3 FETs.
Can I replace these FETs with more powerful FETs to keep it cooler?
If so, is there any specific FET I can use to replace the existing FETs?

Thanks so much.
Regards
Richard T

 

[sonnetg]

This controller of mine has 3 screws shown on the outside of the controller casing. So, i think only has 3 FETs.
Can I replace these FETs with more powerful FETs to keep it cooler?
If so, is there any specific FET I can use to replace the existing FETs?

Thanks so much.
Regards
Richard T

I am not an EE, so can't speak to that, but if you have the controller mounted on the bike frame to let it air cool, it shouldn't cause the the FETs to melt or anything. I also try not to push my mini controller too hard, especially during long uphill climbs.

Do you keep your controller enclosed in a bag or pannier? How do you have it mounted on the bike?

Here's a pic of my Ebikling 36 volt controllers. I haven't opened these up, but I would suspect the smaller one is 3 FETs screwed on to the body to dissipate heat. The bigger controller barely gets hot, but the smaller one does get pretty warm to the touch after 10-15 minutes of hard riding. [The bigger heat sink definitely helps keep the controller much cooler]

 

[d8veh]

Most small controllers I have used have only 3 FETs. The bigger ones' have at least 6 FETs and more. Bigger controllers can push more Amps and not heat up as much. It should not matter whether you motor can handle the current or not. The motor will simply consume the current it needs, no more..no less. If the controller is smaller, the motor will squeez the controllers harder for more current, hence the controller heats up more...at least thats what I observed.

This controller of mine has 3 screws shown on the outside of the controller casing. So, i think only has 3 FETs.
Can I replace these FETs with more powerful FETs to keep it cooler?
If so, is there any specific FET I can use to replace the existing FETs?

Thanks so much.
Regards
Richard T

Those three screws are for the heatsink bar to which the 6 mosfets are attached. That's a 6 mosfet controller!

 

[sonnetg]

Those three screws are for the heatsink bar to which the 6 mosfets are attached. That's a 6 mosfet controller!

Wow...That's awesome. So is the bigger controller with 6 screws a 12 FET controller?

I haven't opened it up, but i suppose it would look something like the one pictured below:

Thanks for correcting. I might open the controller up to take some picutres, but i wonder how difficult it would be to put it back together. The box seems to be enclosed, and the only thing which seems to be holding the circuit in place are the FET screws and eight extra screws on the side panels.

 

[RichardT]

Generally, the bigger the controller, the more power it can handle, but don't get a bigger controller unless there's a way to regulate the current to what your motor and battery can handle because bigger controllers generally allow more current.

Show us a photo of your motor and tell us what battery you have, and we should be able to advise you what you can do.

Controllers often run warm, but they shouldn't be so hot that you can't hold it against your skin.

Hi D8veh

Attached are photos of my controller and battery which is about 7cm thick (not visible from photo).
Hope you can advise further.

Thank you.

regards
Richard T

 

[d8veh]

The 350w written on it doesn't mean anything. It's a normal 6 mosfet controller rated at about 7 amps. You can go as high as 20 amps max, but there's lots of provisos. The faster the motor, the more time the controller will be giving its maximum power, so the hotter it will run. If you put a 300 rpm motor in a 26" wheel, it'll definitely overheat. A 260 rpm motor would be OK up to about 18 amps as long as you don't have long hills. A 201 rpm motor (15mph) would be OK up to 20 amps, again as long as you don't have long hills or weigh too much. Another consideration is airflow. Those figures are for an enclosed one. If you put it out in the air-flow, it'll run a lot cooler.

Whatever controller you have, it can be upgraded. On some bikes, the compartment is too small to take a bigger one, so you have to be more creative with installation. You can upgrade the mosfets, but unless you're used to doing those sort of electronics repairs/modifications, I wouldn't recommend it because everything is packed in very tight. It's easy to damage the pcb or bridge a connection, which will condemn it to the scrap bin.

To recommend an alternative, we need to know how much space you have, and we need to see what connectors you have and their functions. Do you have a LED or LCD control panel?

 

[chas58]

What advice are you looking for?

Definately avoid heat. I have a small one like that running 300 and 330rpm on a 26" and 700c wheel. In a bag, it gets warm and then eventually dies (usually after running full power over an hour).

I put it in open air and on a heat sink (attached to a aluminum bike rack) and it has worked fine for years since then.

Does that answer your question?

Motomech likes the elifebike 36v 17a controller. That one is HUGE compared to yours, but has a similar power rating (although it looks like yours is 13amps).

Generally, the bigger the controller, the more power it can handle, but don't get a bigger controller unless there's a way to regulate the current to what your motor and battery can handle because bigger controllers generally allow more current.

Show us a photo of your motor and tell us what battery you have, and we should be able to advise you what you can do.

Controllers often run warm, but they shouldn't be so hot that you can't hold it against your skin.

Hi D8veh

Attached are photos of my controller and battery which is about 7cm thick (not visible from photo).
Hope you can advise further.

Thank you.

regards
Richard T

 

[sonnetg]

I have the same exact mini 36v controller, which came with the stock motor kit. I purchased another controller as a backup, but the aftermarket controller is 12 FET and nearly 2.5 times larger. As long as you have it air cooled, you should be fine, most of these controller have been known to have blown a FET or two when over-volted. As long as you stay within the spec as rated on the controller, you should be fine. Other option would be to keep few spare FETs in hand or simply purchase an extra controller, if you are paranoid like me.

Other than that, not a whole lot can go wrong with these.