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  1. themotorman

    Motor inductance, controller PWM frequency vs BEMF & RPM

    I have a similar problem with my system. I did not consider the inductance problem until my controller failed. Now I have to go back to basic electronics. ( The controller is a servo drive from A-M-C with IGBT switching as it a high voltage system , nominal 360 volts.) One equation (1) that is...
  2. themotorman

    storing LIpo not doing OK

    I bought some Lipos, GBS type, 20 Ahr in 2010 and they were stored in California coastal climate and not used for three years. I charged them during that time when they got below 3.1 volts and thats it. Tried to use them now and those that I have tested, 6 of the 112 total, have only about...
  3. themotorman

    scale up quadracopter idea

    It would be farily simple to take a toy quad and upscale it and keep the control system . The response time for a larger copter would be slower so this should still be stable. Taking the pwm signal and making it drive a 3 phase PMBM motor would be easy . I would want to use a cobalt steel...
  4. themotorman

    How to log voltages of a lithium battery 16S6P?

    Solved ( I hope!! ) you put 5 volt zeners across all the cell inputs to the chip, thisa makes sure that even with an open cell or cells oyu cannot get more than 5 volts across the chip inputs, that is a safe voltage. I haven;t tried to test this by deliberatley opening a cell connection as it...
  5. themotorman

    How to log voltages of a lithium battery 16S6P?

    The max11068 and the eval board they provide does work to provide detailed monitoring of the pack. However I have been using these for a large pack of 7 x 16 cells ( 400 volt ) and found a failure mode possibilty due to an open cell or open wiring to one of the monitoring inputs to the 11068. If...
  6. themotorman

    Open Source Controller - 144v 500 amps

    MOSFETs do parallel well as they have positive resistance slope so if one heats up too much the load is taken up by the others. I agree that for high amps IGBTs are a nice way to go. The main problem is switching transients due to the inductive part of the system. The down side of this is that...
  7. themotorman

    BMS using Max680X series

    I found these chips that are intended for monitoring power supplies, they come in different preset voltages but have a 2.5 V that looks useful. It is a three terminal device that provides a signal when the voltage goes below 2.5 volts... mmm ideal fro low bat signal I think, just connect to a...
  8. themotorman

    Can I solder directly to Headway 38120 cells?

    NO NO!! do not solder onto any cell... I know it sort of works but that's Ok for a Nicd that costs a few bucks but why ..OH why waste money destroying ( or risking to ) a Lipo.. Get the correct cells for the job and treat them like gold. The areas at the end are right next to plastic insulation...
  9. themotorman

    LIMnPO4?

    I found the site with testing info, it looks like he knows what he is doing.: The GTL results are about the same as mine.. http://www.candlepowerforums.com/vb/showthread.php?t=255943 Hope this throws some light on these cells.
  10. themotorman

    LIMnPO4?

    I bought one to look at and it is 18 mm dia. x 65 mm long , It does charge to 4.2 volts and delivers about 800 mA-Hrs after two cycles, it also will dump nearly 25 amps into a short. I did accidentally let it discharge to zero, and with much surprise, it recharged OK! This is a long way from...
  11. themotorman

    LIMnPO4?

    I did make a typo the cell size is 18650 ( 18mm diameter and 650 mm long ) and yes, they are readily available on ebay. I bought one to test on ebay and so far it is impressive. Cost for a single cell seems to run from $1.00 to $2.00 depending on quantity. The energy density is amazing but I...
  12. themotorman

    LIMnPO4?

    Anyone have info about using LiMnPO4 lion batteries. As far as I can tell the cost/mile for these is currently lower than LIFePO4. and their energy density is also higher. Life is lower but so is cost. It is a more mature technology too so the cell makers probably know how to optimise them...
  13. themotorman

    Testing the big 15 and 20Ah LiFePO4 cells is tough! *Pics*

    RE FETs at high current. I bet that the gate fails first!! You need to make sure that you do not have too much inductance that will reduce the gate voltage then you will be in the resistive part of the FET and boom!! It is very very hard as you say to switch at such low voltages BUT the problem...
  14. themotorman

    Headway Pack Builders thread

    I suggest that you consider copper /tin plated braid rather than straps. The straps transmit vibration from the car and when one cell moves ( and it will !) with straps the force goes right to the next cell etc. With braid the braid absorbs the energy. You used to be able to buy braid already...
  15. themotorman

    Dead cells OPTIMUM DO NOT BUY WARNING

    I bought 10 packs of 48 volt 20 Ahr from Optimum in China. The packs each contained 16 x 16 cells in a parallel-series arrangement, with BMS for each pack. They all failed within one year due to poor construction and poor BMS. Optimum will not offer a refund or replacement except at full price...
  16. themotorman

    New A123 Prismatic 20Ah cells 480g and 30C

    I can find 20 Ah prismatics for about $30 each but have only Chinese company, not A123's , data. Desperately need real data. If you have any please send it to me directly and also to grp. rdoctorsatgmaildotcom
  17. themotorman

    Testing the big 15 and 20Ah LiFePO4 cells is tough! *Pics*

    I think that the inductance is a bigger problem than you think... or may be you have thought about it. Even a few inches of a straight piece of wire will provide enough Inductance for the circuit to ring.. it is the ringing that kills the mega amp MOSFETS. Very hard to handle.. witness my MOSFET...
  18. themotorman

    Hypothetical: I want to Build a LifePo4 battery- But How?

  19. themotorman

    LTC6802-2...any good?...alternatives?

    still looking for a BMS for my 8 packs x 50 volt 20 Ahr. =400 volt bus system...anyone have completed system for this? I am ready to buy. Also need the batteries!! The ones I got from ????? are no f@#$#@ good. Private email me if you want details at rdoctorsATcoxDOTcom.
  20. themotorman

    Got it

    Try running the pack until it cuts out and then try to recharge it immediately. This is a tough test for a LiFePO4 pack but ESSENTIAL as the BMS MUST cutout before ANY cell drops below 2.1 volts. If not the cell will be a dead short and the whole pack almost useless. One problem is that the BMS...
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