Boost converter 3.3v to 36V??

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colin9876
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Boost converter 3.3v to 36V??

Ive just been given a spare 100ahr Lifepo4 cell, so neat, and can do 3C (300amps)

Just thinking I could use just one to drive my 200w scooter if I could get a 10x Boost converter to convert the voltage up to 36v at the expense of the amps dropping - 25amps will be more than enough.

Does anyone know where I could source something like this?

Using one large cell and boosting would save balancing pack problems, Ive searched for something like this in the past but never seen anything that can output more than 2amps!

marylandbob
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Re: Boost converter 3.3v to 36V??

While POSSIBLE, such a conversion from 2.8-4.0 volts up to 36 volts is far from practical, as the input voltage range is so low that a significant proportion of your battery power would be lost as HEAT. Losses in semiconductors and wiring (cables to handle 250 to 350 ampere input) would be much higher at this low input voltage than at a higher input, such as 12 volts or more! (This is because the "ON resistance" of the semiconductors becomes a greater percentage of TOTAL circuit resistance at lower input voltages) At best, your 100 ampere-hour battery might give performance similar to a 7 ampere-hour 36 volt battery pack. You would also have to arrange for SPACE to mount the D.C./D.C. converter, and dispose of its heat. (With 2 or more cells,at 6 volts or better, losses would be considerably less)If 25 amperes at 36 volts is required, it is also likely that current drawn from your 100 AH cell would EXCEED the 3C rate, when cell voltage is low, and usable ampere-hour capacity is decreased at high discharge rates.--Overall, I advise against it, unless everything is FREE, and you just want to experiment.-Bob

Robert M. Curry

colin9876
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Re: Boost converter 3.3v to 36V??

Thanks Bob,
where could I get such a boost converter and Why does there have to be such big losses?

Say if the battery just charged some 5v ultracaps. Lets say 10 of those in a row the batt charges each one for a second then goes on to the next. The string of capacitors is getting continually refilled one by one.
So it would need a timer/switcher circuit but thats all?

Even simpler - is there anyway this is possible
....If run 10 sets of parallel wires off a batt is there some way with diodes they can be strung together in series like it was 10 seperate batteries?

marylandbob
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Re: Boost converter 3.3v to 36V??

Call me on the telephone, to discuss in detail! 301-439-3873 Now, Wednesday night, is OK.-Bob

Robert M. Curry

colin9876
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Re: Boost converter 3.3v to 36V??

Sorry Bob wasnt able to call as was at work (and in different country!)
Are you able to give me any more info on here if theres any easier way with diodes of such like to take parallel wires of a single batt and string them together as if it was a chain of batteries.
Boosting a large single lifepo cell could have advantages over current pack designs, if the voltage uplift could be done fairly efficiently!

marylandbob
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Re: Boost converter 3.3v to 36V??

Stepping up 3 volts to 36 volts at high 36 volt amperage, such as 20-30 amperes, is not very efficient, due to losses in the semiconductors being very significant! A typical switching transistor may drop 0.30 volts when turned ON, and switching 300 amperes at 3 volts from your battery,(90 watts wasted) and this 0.30 volts would represent 10% of the power from your battery, lost as heat. To this loss, you must add the loss of the D.C. convertors inductor/transformer, and the rectifiers, easily another 10%. (Switching transistor drop of 0.30 volts with a 12 volt battery, and 75 amps, for the same 36 volts of output power, would result in only 22.5 watts lost, with the higher input battery voltage)--Using DIODES to steer the 3 volt input will result in even WORSE performance, as suitable diode would drop even MORE voltage at the amperage required. Transistors of some type are RRQUIRED, and they are all less efficient at low voltages. ESPECIALLY below 10 volts input. A reasonably efficient circuit would also be somewhat large and heavy, due to the size of the conductors, heat sink, capacitors, transistors etc. that would be rquired.--All these items become smaller, lighter, less expensive and more efficient at higher battery/input voltages. (If doing as you proposed were practical/efficient, it is very likely that others would have done so, long before now! If you had at least FOUR such cells in series, such a solution would be more practical, but still less efficient, somewhat expensive and bulky, compared to building a 36 volt battery of similar kilowatt-hour capacity.--What country are you in?

Robert M. Curry

colin9876
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Re: Boost converter 3.3v to 36V??

Thanks Bob,
Im in UK. Ok using 4 cells would be ok, that still saves another 8 by boosting the 12v to 36v
Im going to have a search round and see if I can fin a booster that can handle 500w!

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