Confused on all these kit wattage claims, HELP PLEASE

:? I am trying to figure out just how many watts my motor will be putting out. In doing much (confusing) reading on the net trying to figure this out I have come up with..

Mac kit at 500/1000 watts = 500 at 37v and 1000 at 50.4v

When I figure it out with the Battery Max Discharge amps {which are limited by the BMS to 12 Amps) I get.... (12a*50.4v) = 604.8 Watts

This is all from a kit I ordered. If the items supplied in the kit are limited to 604.8 watts by the manufacturer then how can it be claimed as a 1000 watt kit as is being done.

Please, this is not a rant at the manufacturer as I had all this information at the time I made my order (in fact I made the order partly on the good reputation of this manufacturer).

I am just trying to figure out if all the claims I see on Ebay and other places are in fact "bullshit" ?

Was the battery packaged with the kit, or did you select it separately?

gaisom said:

When I figure it out with the Battery Max Discharge amps {which are limited by the BMS to 12 Amps) I get.... (12a*50.4v) = 604.8 Watts

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That would be the output limit of the battery pack. You loose about 10-20% of that efficiency through the controller. First, select a battery system that can output the max amps of the controller. As an example, my battery pack is rated for 20C, I have 10ah of 100V, so that's an output rating of 200A. My controller is 40A, so that means it can draw up to 4000W. Max efficiency of my motor is ~85%, so the max output of the motor is 4000x.85, or 3400W. So even though your battery is capable of 604W, you won't get that much output at the motor. Probably closer to 500W. A motors watt rating is a continuous duty rating unless other wise stated so it can output many times more than that for shorter periods of time before it melts. And one can rarely actually draw the max amperage of the controller for more than a second or two because it goes down once the load is not as great.

gaisom said:

:
I am just trying to figure out if all the claims I see on Ebay and other places are in fact "bullshit" ?

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Very often, yes.

Standard motor ratings are what the motor can handle at a 100% duty cycle. Back in the day, most vendors stuck to that, and the common bike motors were all listed as 500 watt. Then someone got the idea that a 48 volt 22 amp controller could peak at ~1000 watts and you saw Ebay flood with people selling 1000 watt kits. A bit deceptive, but essentially true, when in the fine print they noted that it was 1000w peak output. But there are plenty who never bothered to explain they were rating on peak output.
Things get even more confusing since some vendors were actually selling real 1000w motors, and it became nearly imposable to tell without buying one.
later you had people selling these "1000 watt" kits along with battery packs that just couldn't perform to that standard, but they kept sort of honest by calling it a 1000w kit with optional battery.

Mix into that a cultural difference that is hard to fathom, where Honor and honesty are defined completely differently, and you get some real trouble.

In china where many of these Ebay vendors originate, it is considered honorable and expected to exaggerate your product to the extreme. Its part of the sales process and the buyer fully expects the seller to be exaggerating. the buyer is then expected to exaggerate how bad they think the product is, and negotiations begin. this is normal and moral in their culture.

In western culture, we a low tolerance for BS, and expect the seller to tell us exactly what they have. My uncle worked in china with a US trade delegation for 10 years trying to get a market for US goods over there. One of the unique problems he was running into was the Chinese were mildly insulted by our straight forward sales practices. They felt as a buyer that a seller who wasn't exaggerating did not find them worthy of negotiating with.

Caveat Emptor

wesnewell wrote:

select a battery system that can output the max amps of the controller. As an example, my battery pack is rated for 20C, I have 10ah of 100V, so that's an output rating of 200A. My controller is 40A, so that means it can draw up to 4000W. Max efficiency of my motor is ~85%, so the max output of the motor is 4000x.85, or 3400W. So even though your battery is capable of 604W, you won't get that much output at the motor. Probably closer to 500W

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I think this is one of my main confusion points. To me the main part of any system has to be what is supplied to the motor. The kit I have bought has a 40 amp controller which I requested since I am planning on using the Controller with any future upgrades. I will limit the controller using either the programming cable supplied with it or the Cycle Analyst Version 2.3

The battery I bought (14S 7P, 50V 16.4Ah Samsung SDI Battery Pack uses the SDI ICR18650-22P 3C rated cell) does not match the controller. The controller recommended was a 30a. I figure using the 30a*50.4v=1512w formula and your input it will probably be about 1250w or so without figuring any battery info in at all. So I am seeing some of what is causing all my confusion. Then when you start using the CA simulator and find that all this is figured at Full Throttle and when you drop back to around 45-60% throttle your range drops drastically and you can actually get into heating problems it confuses me even more. But, I am starting to see the light!

Avitt said:

Was the battery packaged with the kit, or did you select it separately?

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The battery is with the kit, but the kit is a mix and match so I am selecting it myself.

gaisom said:

wesnewell wrote:

select a battery system that can output the max amps of the controller. As an example, my battery pack is rated for 20C, I have 10ah of 100V, so that's an output rating of 200A. My controller is 40A, so that means it can draw up to 4000W. Max efficiency of my motor is ~85%, so the max output of the motor is 4000x.85, or 3400W. So even though your battery is capable of 604W, you won't get that much output at the motor. Probably closer to 500W

Click to expand...

I think this is one of my main confusion points. To me the main part of any system has to be what is supplied to the motor. The kit I have bought has a 40 amp controller which I requested since I am planning on using the Controller with any future upgrades. I will limit the controller using either the programming cable supplied with it or the Cycle Analyst Version 2.3

The battery I bought (14S 7P, 50V 16.4Ah Samsung SDI Battery Pack uses the SDI ICR18650-22P 3C rated cell) does not match the controller. The controller recommended was a 30a. I figure using the 30a*50.4v=1512w formula and your input it will probably be about 1250w or so without figuring any battery info in at all. So I am seeing some of what is causing all my confusion. Then when you start using the CA simulator and find that all this is figured at Full Throttle and when you drop back to around 45-60% throttle your range drops drastically and you can actually get into heating problems it confuses me even more. But, I am starting to see the light!

Click to expand...

So the battery is not really BMS limited to 12A?

You've got a few things wrong,unfortunately.
Can we have a link to the battery? I've never heard of an ebike battery limited to 12 amps. Even the weakest 8aH 36v ones are normally well above that.

When you reduce the throttle, the efficiency goes up, not down. Efficiency of a hub-motor depends on speed more than anything else, but when you reduce the throttle, the whole efficiency curve moves down the rpm/speed axis so that you can get higher efficiency at lower speed as long as you have enough torque to maintain that speed.

All your calculations above are the power from the battery, which is not what the motor gives out. You have to know where you are on the efficiency curve to know the output power. Generally, if you have full throttle, and your speed drops below 50% of the maximum no-load speed, you start to get efficiency of 50% and below. When your motor is really struggling up a hill, efficiency can go below 30%, so output power goes right down although torque goes up, which is what's needed to drag you up a hill.

When you're on the flat at full throttle approaching the maximum no-load speed, you won't get anywhere near the maximum current from your battery or controller,so your input power will be down.

You need to have another play with the simulator to get it all figured out.

The only way to truly know your wattage is by putting a wattmeter on the system. Then you at least can measure watts leaving the battery, and take some guesses about system efficiency for watts to the rubber.

Cruise at full speed is often 80% efficient or more. But a stalled motor lugging up a hill too slow can easily drop to 50% efficiency.

When selecting a kit, the best guess as to real world wattage under full load like a steep uphill start, is to multiply controller max amp by battery voltage. So a 40 amps controller and a 48v battery should produce up to 2000w. Since a Mac is recommended for use under 1500w, a 30 amps controller is the most I'd choose.

Then from there, you need a battery rated for more than 30 amps, if you really plan to pull max amps a lot. As long as it's not a bitch to carry, you can never have too much battery. The battery will appreciate it a lot if you cruise at half it's rated amps, or less.

Can we have a link to the battery? I've never heard of an ebike battery limited to 12 amps. Even the weakest 8aH 36v ones are normally well above that.

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I did have it wrong. I gave the amp limit I was going to set thru the controller, not the actual pack specs. Here is the Link to the pack I wanted.

http://em3ev.com/store/index.php?route=product/product&path=35&product_id=134

Things are a little up in the air about that pack so this is a good time to be discussing it.
I may have to change to a
High Energy INR18650-29E (NCA Cell, 3C Max rated cell, with approx 2.8Ah nominal Capacity). Since the SDI ICR18650-22P 3C rated cell are going to be out of stock for a bit.

I am unsure if this will be a beneficial change or not at this time.

Dogman Said:

When selecting a kit, the best guess as to real world wattage under full load like a steep uphill start, is to multiply controller max amp by battery voltage. So a 40 amps controller and a 48v battery should produce up to 2000w. Since a Mac is recommended for use under 1500w, a 30 amps controller is the most I'd choose.

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Yes, I agree. Which is why I plan on limiting it using either the BMS programming or the Cycle Analyst.