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eBike Modification - Controller and Amperage questions

Hello! I am looking to mod my eZip echo ride 2 bike.

I was looking at the 36v controllers on this site's store. But I am really confused. One says it is for up to 500W motors. But it also says: "Maximum current 25 Amps". Ohms law means that at 25A with 36v, I'm running 900W. So shouldn't that controller be called a "900W" controller and not a "500W" controller?

The problem is that I don't want to go over a 900w to the motor. A higher output 36v controller that is rated for "up to 650 Watts motors" has maximum current of 30 Amps, which would actually mean up to 1080 watts. This is why I'm confused.

I'm assuming that the controllers work by controlling the output current? Using the throttle position as an indication of how much current to output? Is this correct?

I'm having a hard time with this too: Stock the bike is 24v, the stock controller states 25A on its sticker... Ohm's law makes it 600W max output. The motor is "rated" at 450W. So is the bike already b4eing pushed passed the rating at stock configuration? I wouldn't think they could for liability reasons. However, If you "reverse" the math and figure 450W rated motor at 24v that is 18.75A, not the controller's sticker stated 25A. Aside from grabbing my ammeter, how am I supposed to know what amperage my stock system is supposed to be outputting?

Am I missing something? Why does the specification differ from the Law of Ohm's in every example I've provided?

Maybe I am missing how the controller comes into play. Is the stated max output not necessarily the max output to the motor? If so, shouldn't the max motor output current be listed as a separate specification detail? Is there another factor here that I have not taken into consideration? It just doesn't add up for me. I hope maybe since you guys are the EBIKE kings you might have some information in this regard.

Also, do you have any suggestions on upping my system without frying the (stock 450w) motor? I'm toying with the idea of running at 36v system with a controller that will push my motor to about 800-900W max. But again that is based on an assumption that with a controller I would get the stated 25 max current output to the motor.

Thanks a bunch for reading and I appreciate any assistance you can provide me.

Shaun 8159

1 person likes this idea

The Watts rating is continuous and Amps rating is intermittent - that is why they do not relate to each other mathematically. A controller's maximum current rating indicates its intermittent duty rating (for accelerating from a standstill and going up short inclines), while its Watts rating indicates its continuous output rating capability. They build controllers that way so they have enough power for intermittently heavy loads such as getting up steep driveways and ramps. If you continuously run a controller at its maximum current rating it will probably burn out before the motor does. The amount of current that a controller outputs depends on both the load that the motor is placing on the controller and the position of the throttle.

For a 36 Volt 450 Watt motor a controller with a maximum current rating of 25 Amps will be a good match for it. As long as the motor is not running too hot then it should last a long time. If the bike is being used for going up long hills then you might want to stop after a while and check if the motor or controller is getting too hot and throttle down a little if either one of them are to keep them from burning out.

You can use a controller that is rated for significantly more Watts than the motor is rated for as long as the motor is not getting too hot while it is in use, the extra power could be used intermittently for climbing ramps and short grades, but not continuously, otherwise it would most likely overheat the motor. The safest thing to do is use a controller that is rated for the same or slightly more Watts as the motor is, and to take it easy when going up long or steep hills.

You rock, thanks for the excellent explanation! That cleared it right up for me.

How would I go about making sure of controller compatibility with my other electrical components? Such as the throttle. I'm not sure what kind of throttle my bike has. It connects to the stock controller and is only 2 wires. At the controller (which I haven't gotten to dis-assemble yet) there are also connections for the brake stop, the TAG/PAS switch, the cadence sense, and the motor, obviously. What controller options do I have for this type of setup at 36v 25A?
EDIT: Just doubled checked and the throttle wire is a 3 wire afterall. When I counted 2, it was because I was looking at the battery level status LED wires. At the controller its a total of 5 wires to the throttle. 3 for the throttle positioning and 2 for the LED light output.
So it looks like about 4.2 or so volts of power is supplied to the throttle wires...
What is the normal current output rating of that rail and is the 4.2 voltage regulated?
Could I steal 2A off that circuit to charge my phone or would that prohibit the throttle from working correctly?
It is virtually universal for electric bikes to use hall effect throttles with a 5V DC input and 0.8V-4.2V output. I would assume that the bikes throttle has these specifications. These are the throttle specifications that all of our controllers require. We have around six 36 Volt controllers with 25 Amp maximum current specifications available on this page:

I do not have any specifications for the current output rating of the throttle connector for any of our controllers. Since most hall effect sensor ICs only require a few milliamperes of power to operate I doubt if any controller would put out more power than is needed to run them. I would use a separate DC-DC converter for phone charging to avoid risking damage to the controller.

Ok awesome, thanks again! I actually did go ahead and get a DC-DC converter for charging my phone, so I will not have to worry about the controller with with that.

So the only other question I had was about the "cadence sensor" input on my eZip. This is the input that controls the pedal assist (when I start to pedal, the motor kicks in on low power). I don't see a connection on the controllers on your site for this input or the switch for this function. How would I be able to hook that up? I notice the sensor has a 3 wire plug too.
Also, are the controllers over voltage protected as well? I could not fins specs for the upper cutoff, only the low voltage cutoff. Thanks again!

The only controllers I know of that we sell for brushed motors which have a cadence sensor input are the OEM Currie (eZip and IZIP) electric bicycle controllers. I can not recall that any of our universal controllers for brushed motors have cadence sensor inputs. Most of our controllers for brushless motors have cadence sensor inputs though. Any of our controllers that do not have a cadence sensor input will not work with cadence sensors - they can only be controlled with a throttle.

None of our controllers have over Voltage protection. It is rare for a battery pack to be overcharged by its battery charger so over Voltage protection is not a feature that is present on any speed controllers that I know about. Most controllers can handle Voltage levels above what they are rated for so I do not think that higher Voltages are a problem for them. A lot of people over Volt Razor MX500 and MX650 electric dirt bikes from 36 Volts to 48 Volts and use the original 36 Volt controller without any problems.

Sweet, you have been very helpful!! Thank you very much for the information!


You are welcome for the information and thank you very much for your questions. If you have any further questions in the future please do not hesitate to ask.

A few more questions, getting ready to embark on this adventure.

What are the dimensions of the Item # SPD-36500A controller?
Other than where the wires come out, is there any difference between that and the Item # SPD-36500B controller?

What is the difference between the $35 controllers vs the $40 ones? (Ex: SPD-36500 is $34.95 ; SPD-36500A is $39.95).

Thanks again!


I just had a chance to measure the SPD-36500A controller and its dimensions are 3-7/8" x 2-7/8" x 1-1/8". Its wires are approximately 3" long.

The main difference between the SPD-36500A and SPD-36500B controllers is that they are designed and made by different factories. They are both made by very good factories though and we do not have any quality control problems with either controller. The SPD-36500A is carefully sealed around its wires and case lid with silicone rubber so it is water resistant, while the SPD-36500B is not sealed at all and water can easily get inside of it.

The $34.95 SPD-36500 is made by the same factory as the $39.95 SPD-36500A and they are both sealed and water resistant. The SPD-36500A is larger and has a larger heat sink than the SPD-36500 so it should be able to handle higher loads without overheating. The heat sinks of both of these controllers is on their bottom side so they can be mounted to a steel or aluminum plate or beam to enhance their cooling capabilities.

The SPD-36500B uses its entire case as a heat sink so if it is not being attached to something that will draw heat away from it then it may be the better choice as far as cooling goes.

Hello! Once again thank you very much for the detailed and helpful info. Since I rode my bike to work today, I was able to measure my "controller compartment" and I went ahead and placed my order for the 36500A controller. Being sealed is a big advantage point for me, as is being a bit larger and able to handle more heat and added cooling options. Since I will (just barley) be able to make it fit, it was hands down the one for me to order.

Thanks again! I am sure I will be back as I start making more modifications to my bike. 

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