Simple 330V charging circuit

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megacycle   100 kW

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Simple 330V charging circuit

Post by megacycle » Apr 27 2019 4:43am

I was thinking about this and if and how it could work to fast charge a large Lifepo4 EV pack that has good BMS protection and where there is an ample supply available of say 150A+, 415V, 3phase.

Example 30kW pack at approx 3C in about 20 mins.

Presently only come across this type of charging for small scale wind turbines wound for 3ph and vehicle battery alternators.
HPM5000BGenerator-1.JPG
Simple 3 phase rectifier for battery charging
HPM5000BGenerator-1.JPG (14.32 KiB) Viewed 377 times
If you've seen it before, the ripple on the rectified dc waveform out, is quite a lot cleaner than a single phase supply due to six sets of interweaving rectified peaks giving this waveform.
The waveform should be further smothed by the battery acting as a very large capacitor.
power98.gif
Rectified dc waveform out from 3 phase supply
power98.gif (22.33 KiB) Viewed 377 times
A possible improvement came to mind in using a 3 phase thyristor or IGBT bridge and a manual or controller circuit to control the voltage across the battery pack.
CR1.JPG
Thyristor bridge circuit
CR1.JPG (15 KiB) Viewed 377 times
With resulting reduced RMS waveform
593E6FDF-A150-4539-9876-76EAAC45D17E-215_46B3AE99-0419-71F3-ED6EB1A2FEBEDD45.jpeg
RMS voltage reduction by thyristors
593E6FDF-A150-4539-9876-76EAAC45D17E-215_46B3AE99-0419-71F3-ED6EB1A2FEBEDD45.jpeg (28.87 KiB) Viewed 377 times
The voltage out from rectifier would be approximately 330V dc so I was thinking that a pack made up of 330/3.6 fully charged Lifepo4.
92 cells would give approx 3.58V each.
and 30kW/330V approx 90Ah each.

Any thoughts of how crazy šŸ˜ this might be would be appreciated.
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amberwolf   100 GW

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Re: Simple 330V charging circuit

Post by amberwolf » Apr 27 2019 2:10pm

If you look around for "bad boy" (badboy) charging / charger you'll find posts and threads and pages about this type of thing, pros, cons, circuits, etc., both here on ES, on DIYElectricCar forums, and other places. Sometimes called "freddy" charger, "poor man" charger, etc.


Some thoughts off the top of my head:
--since there's no current limiting (other than melting point of the wires and components), how do you deal with the problems this causes in the cells? And how do you prevent the wall breaker from popping?
--what happens when the BMS for the pack tries to cut off charging due to HVC, but the ripple goes above and below that?
--what does the ripply voltage do to the BMS electronics?
--what happens during balancing stage, since the ripple will go above and below the voltage needed for this? (is the BMS dumb, or "smart" and getting confused?)
--does the pack actually have enough capacitance to smooth it sufficiently, as it reaches full state?
--how does the pack's constantly changing internal resistance affect the system during charge?
--when the rectifiers fail (from whatever cause), how does the pack react to the raw AC waveform across it? (what kind of fire prevention or containment do you have?)


Other considerations are in the various stuff about bad boy chargers around the web.
one possible websearch:
https://www.google.com/search?q=bad+boy+charger+-buggy

One previous thread:
https://endless-sphere.com/forums/viewt ... 14&t=90066



FWIW, car alternators do actually have a regulator, as well; they aren't just raw rectified output (though they may still use the FLA battery as a capacitor to filter it, and if the battery goes bad, the resulting AC noise can be heard in sound systems onboard; don't know if it could damage anything).

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