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Old 09-26-2015, 11:59 AM   #2087 (permalink)
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Originally Posted by danibjor View Post
Hi all. New here..
As e*clipse says - Welcome!

This is the project that wants me to try going electric. One of my criterias is that the car should perform like it did (or better) on petrol.
A good criteria for a fun-to-drive car. My standards are a bit lower - I need to get to work and back home without getting run over by other drivers

One thing I have in mind is charging. I don't want to use a lot of space (and weight) on a big charger to top off the batteries needed to keep up with inverter. I've been doing some research and found this:

If you look at the 3th picture - "all you need" is a rectifier and a filter on the mains to charge the car using the motor controller's regen function. - or is it?
I looked at the third picture. What I see is ..
- the bridge rectifier appears to have negative tied to the negative bus on the battery pack
- the positive of the rectifier goes to one lead of the motor - lets call it C phase
- the control algorithmn is then to cycle the positive C phase transistor to allow current flow into the battery positive, charging the battery pack
- the controller sees battery charging as negative amps and positive volts on C phase
- the controller may track pack voltage, and it may track phase to phase voltage on the motor ... but it likely does not track C phase to pack voltage

This is not really what I would call 'regen' but it sounds quite interesting as long as your battery pack voltage can be charged by the available voltage from your outlet.

My 125V pack can be charged by 110V * 1.414 (root 2) = 155.5V peak bridge rectified DC with AC ripple on top. I have seen about 160V DC if the voltage is closer to 120VAC, including bridge diode drop of about 1.5V.

If I were to run the Siemens motor in a car, it would likely be closer to 350VDC on the pack, which is above 220V * 1.414 = 311V .. so you get into the boost stuff that e*clipse talks about

If it's doable - is this somthing that this controller can handle?
My opinion would be - not yet.

Another question: How does the controller know the voltage sendt (also with regen) back to the batteries? I mean, so you don't get an early new years eve show..
I know that the pack voltage is a setting in the controller, but I don't know if the pack voltage is measured.

I think that the voltage and current to the motor are measured while the controller outputs are in the middle of their ON state - am I right, Paul?

The batteries are actually quite forgiving about charging at a higher voltage. The voltage applied minus voltage of the pack gives the electrons incentive to move. The internal battery resistance (a vague concept on it's own) determines the charging current. As the batteries 'fill up' the pack voltage increases, the charging current drops. The trick appears to be to determine when to stop charging and declare the batteries 'full' without overcharging them. The battery suppliers seem to describe a recipe, perhaps 2, that will get you to 'charged' batteries. If you don't follow the recipe, you need to count coulombs (amp-hours) out of and into the pack very carefully .. or try stopping early and measuring how much energy you can get back out to figure out how much more you could have put in ...

Other PWM chargers appear to check current out in the middle of the charge pulse and voltage of the pack in the middle of their 'off' period

- About me: Engineer in automation (industrial) - great interest in programming, electronics and cars
Another automation guy! Woohoo!
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