This post is not meant to be a flame, it's meant to be educational because the math and reality do not support what you are saying. If you only look microscopically at RDSon what you are saying makes sense, but RDSon is only one small factor and is only the dominant heat producer under certain conditions.andreym wrote: There is no way you can get more power using 150v FETs at the moment than 100v ones.
Simply calculate maximum current and power dissipation at the same current for IRFP4468 and IRFP4568
you will be surprised. because 150v ones have twice RDSon compared to 100v ones. This means in the same conditions you can only use half the current.
But wait a minute, you have only 1.5x the voltage, not 2x !!!
In total the most effective way to get maximum power is to go 100v FETs.
Most losses come from switching an diode losses unless you are using full block commutation (no PWM or at least very little), then the conduction losses become your dominant issue. The Xie Chang controllers use full block commutation at 100% throttle under some conditions do, but with or sine wave you are always switching at your PWM freq unless you switch to trapezoidal wave forms. Lebowskis controller chip does this. Even if you do go into full block commutation as long as your thermal management is good it doesn't matter that the dominant losses are conductive.The IRFP4468 and IRFP4568 are both capable of good power with the IRFP4568 > IRFP4468 most of the math I have run if you read the datasheets and know the package limitations. More voltage at the same amps = more total watts. 80V * 200A = 16,000W, 120V * 200A = 24,000W. Same amperage, just higher voltage. Myself and others have proven many times higher voltage is a great way to get more power, it's why IGBTs exist. There are not many high speed hub motors and a downside to many higher KV hub motors is that they end up having higher start up losses in stop and go traffic unless they can produce an adequate amount of torque.
92V max, that is NOT A SAFE VOLTAGE for an IRFP4468. You max safe voltage is going to be around 80V fully charged and even that only gives you a 20% safety margin which would be the bare minimum for a commercial product IMO. If you switch to an IRFP4568 and 150V capacitors you end up with a much better controller.
The TO-247 package has a usable package limit of 120A max due to the legs. Now that you see the package legs are the limit look at the math.
Safe operating area with package limit and 20% voltage safety margin
IRFP4468 = 80V @ 120A, put 2 in parallel and you have a max of around 80V @ 200A = 16,000W
IRFP4568 = 120V @ 120A, put 2 in parallel and you have a max of around 120V @ 200A = 24,000W
If you examine figure 9 in each of these MOSFETs data sheets you will see they are both OK to operate at 120A @ 100C. Since you never run up against the max specs look at the 80C Tc max which is where you should be going into protect mode and limiting output until the temperature starts to drop. At 100C you should be shutting down the controller to prevent any possible damage.
If you do not have anything else in the controller holding you back from running up to 125V, you could greatly improve it by switching to IRFP4568 MOSFETs and 150v rated caps. No need to worry about the RDSon, both of the MOSFETs are low being 2.6mOhm and 5.9mOhm respectively. Heat lost to conduction losses is squat compared to everything else.
Here is a real world example I have tested with the Xie Chang controllers and IRFB4110 and IRFB4115 MOSFETs.
An 18 FET 4110 controller was able to do 140A @ 75V before reaching my 100C thermal limit, an 18 FET 4115 controller was able to do 85A at 125V before reaching my 100C limit, both took about the same amount of time to reach the limit. The 18 FET controller case is the limiting factor for the IRFB4115 based controller because it does run warmer due to unipolor PWM and going into full block commutation at top speed. Even with those numbers, 75*140=10,500W, 125*85=10,600W. Pretty much splitting hairs, pick the right controller for the KV of your motor. When I moved up to 24 FET controllers which have much better thermal capabilities things change a lot. The 4110 controller could do 200A @ 80V and be in spec, 16,000W. The 25 FET IRFB4115 controller can do 120V @ 200A and be in spec, 24,000W. I wasn't able to get either one of these controllers over 75C Tc (I always monitor the Tc of the FET under PWM as it almost always has the highest losses).
Remember the IRFB4110 has a RDSon of 4.5mOhm vs the IRFB4115 at 11mOhm. The TO-220 case is limited to a max of 75A and with paralleling 4 FETs I derated to 50A per FET. Given good thermal properties you can see that the RDSon really doesn't make much of a difference.
I believe it would be worth your time to solder in some IRFP4568 MOSFETs and put a temp probe on the case of the MOSFET body and datalog it's temp vs and IRFP4468 based controller. Change nothing besides the MOSFET and see how much of a difference there is in the temperature, I'm pretty sure you will be surprised how little difference there is. The difference will probably be so small that you will have problems measuring it reliably except maybe under a unique operating mode (I don't know exactly how your controller works so I am unable to tell you the worst case scenario, but the above info should help you figure it out).
I don't know if you are the person who designed the power stage on this controller or who has been involved, but have them run the math on losses and you will clearly see that it makes more sense to go with the IRFP4568 MOSFET. The math is pretty easy, I've previously posted a spreadsheet long ago which will calc the switching losses for you.
The DIY ebike crowd certainly needs better controller choices and the Addapto appears pretty innovative. I personally would like to try one out.
Do you have details on how the BMS is working? You using the LTC6803 chips?
Could you post some detailed photos of the internals. I'm interested in seeing the driver layout and power stage designs. You can PM or email me if you don't want to make them public.
Regards and the best of luck with sales,
Jeremy
P.S. I emailed you about pricing last night. jwolf@dodecahedronsolutions.com
