INCREASE EBIKE SPEED WITH DC BOOST CONVERTER

How about instead of adding more cells, we just buy a 1800W boost converter.

A boost converter is basically a transformer for DC power...... That is adjustable to a fixed output voltage. Plan on using one of these boys to step up my 48v 20ah battery to 72v....

Like here:

https://www.ebay.com/itm/1800W-40A-DC-DC-Boost-Converter-Step-Up-Power-Regulator-Module-Constant-Current/184056719127?hash=item2adaa2a717:g:rRsAAOSw57BdAjJp

Thoughts.....

How about using fieldweakening, where the motor inductors kind of perform the job of the boost inductors ?

please explain what that is and how it works, and how to implement it...

See FOC ( field oriented controllers ).
See field weakening.

In any case, if you need a 72v battery, best is to use one instead of transforming the voltage of a 48v battery, for efficiency at least.

Well, getting back to boosting 36V to 52V, I get 65-70% efficiency. Bike burns 2.25 AH, battery supplies 3.3 AH.

My unit is a 1500W that maxes out at 20A output, but can take 30A from battery. Cost me less than 20 bucks, Bought it as a curiosity.

Or just put in the battery that gives the voltage you want?

docw009 said:

Well, getting back to boosting 36V to 52V, I get 65-70% efficiency. Bike burns 2.25 AH, battery supplies 3.3 AH.

My unit is a 1500W that maxes out at 20A output, but can take 30A from battery. Cost me less than 20 bucks, Bought it as a curiosity.

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AAAAAH Thanks. That's the response what i was looking for.

Are they really that inefficient. I thought these inverter technologies are like 80-90%????

Do these things sag under load, is it constant current or voltage?? You can adjust the voltage right?? I could see using one of these things as a lab bench power supply via a DC wall rectified input...

What was the speed increase from 36 to 52.... Thx

bike4life said:

Are they really that inefficient. I thought these inverter technologies are like 80-90%????

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80% peak efficiency, if you buy the very best. Most that are available cheap are really 70% peak efficiency. Then, peak is attained only in optimal conditions, part of the time. So, considerable amount of extra power will be pulled from the battery. And, the part of power that is the inefficient ‘cost’ of transforming, is lost in heat. The unit must be allowed to shed heat away from the battery because the heat transferred to the cells would affect even more their own efficiency and life expectation.

IMO, that ´cheap trick’ is a deficit. You will produce extra speed proportional to the voltage increase, providing it does supply sufficient wattage to overcome the extra resistance of aero drag. But, the battery will be taxed proportionally also, because of poor efficiency. At the end, you will be paying more than the cost of a bigger battery, because you will wear your actual battery much faster than its life expectation, and benefit only partially of the current that it will supply.

alright thx then. So i guess u are saying to just get a bigger battery......

Sounds good, but i also think this is a good charging system. Can i use one of these boost converters as a e bike charger....
Like take a server power supply 2,000 watts, that turns 120v into 12v or 24v for the server racks, then use a boost converter to dial that into 54v or 72 etc.... Thx
But also do these charger things need to shut themselves off...?? When the 72v of the battery reaches the 72v output of the charger, would no current flow and thus it would kind of self-regulate and shut itself off. Thanks

The speed increase was the same as when I would put a 48V pack in place of a 36V pack. On throttle only, max speeds on my geared motor went from about 20 mph to 24 mph on an actual 50V from the booster. I picked one bike, a 500W geared motor on a 20" fat tire wheel.That bike hit 24 mph on 50V, and inched up to about 27 mph on 60V. Throttle only, and I sat upright.

I did get complete loss of power after a while though on warmer days, and I didn't figure out yet whether it was my controller or the booster overheating.

As a power supply, mine can only put out a higher voltage than the input.

aka Boost-only.

Buck-only is much more efficient.

Buck-boost is harder to find reliable in high-current at a reasonable price.

Cheap Chinese for all these do not get near the advertised current without lots of cooling assistance, finned heatsinks in the airstream would help.

But using converters in general will drop your Wh/km energy efficiency by **a lot**, maybe cut range in half

so again, fine for science experiments, but for "production use", best to choose the right voltage in the first place.

bike4life said:

please explain what that is and how it works, and how to implement it...

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What it is - motors have a "base speed" that they don't want to exceed with normal commutation. With field weakening, the commutation angle is changed so that they can go faster than base speed with the same voltage. Many controllers (like the Phaserunner) do this. It is less efficient than running below base speed, because you are effectively using some of the EMF to cancel out part of the permanent magnet field (hence the name) but a lot more efficient than a boost converter.

Ideally you'd choose a motor/battery combination so that the speed you are usually at (say 25mph) is close to base speed, and then the rare times when you want to exceed it, you use field weakening. That maximizes your efficiency.

Yep, field weakening is a great feature for a controller, especially that FOC controllers usually have very complete setting options and features.

Yet, it has to be for occasional extra speed. If you ride everyday in field weakening speed range, best is to feed the voltage required for that speed, for both performance and efficiency.

I like feeding even higher voltage than needed, to make some extra speed and acceleration available from the speed that I usually ride. It is a matter of safety for me. After the options of braking and swerving, acceleration is one more tool at hand to avoid a crash.