Looking to step-up voltage on a 24 volt Lawn Mower

[captain387]

Hi Everyone,

Looking for some advice from people who have used step-up converters.

I purchased a 24 volt lawn mower which was originally powered by lead acid batteries and were at the end of their life.

Last year I ran the mower on 20ah of 6s lipo batteries and the mower worked great! I charge the pack to 24.6 volts or 4.1 volts per cell.
An upgrade I am looking to make is to slightly boost the battery voltage to get the blade spinning faster throughout the battery discharge (even at 24.6v the mower sounds subdued).
The mower usually draws 15 amps and spikes to 25 amps when hitting a thicker patch of grass.
Looking to boost the battery to 27-28 volts (what the lead acid probably would be at hot off the charger), not really sure how many amps I would require to step-up the 3 - 4 volts.

I was wondering has anyone done this before, any recommendations on step up converters which have stood the test of time.

Thanks,

Jeremy

 

[amberwolf]

some preliminary things to consider:

does the mower actually use a controller? or is it just on/off?

if it uses a controller, then a dc-dc boost converter will only need to handle the max limited current of that controller, which will itself try to protect the boost converter (whcih it thinks is a battery) from overload. (assuming the controller *has* a current limit; some don't, and so they blow up when the blade jams on stuff).

if it only uses an on/off switch, then the *huge* inrush current of starting the motor every time may damage or destroy any boost converter that isn't designed to handle that kind of current (potentially hundreds of amps). might not happen the first time...but it could. (the operating current may be *much* lower than that startup current, and easiliy handled by a boost converter...but the startup current may be far too high) in this case, a sufficiently-capable boost converter is likely to cost too much and be too large, and it may be cheaper and smaller to just use a big enough capacity battery of the right chemistry to not sag or change much in voltage over the required operating time of the mower.

additionally, without a controller, the brush arcing in the motor generates a lot of rf electrical noise, which the boost converter generally isn't designed to handle, so that can also damage or destroy the boost converter. (probably won't...but could).


if you have a wattmeter, i recommend putting it on there between battery and controller, to see what kind of peak and continous currents the system takes. that will help you quite a lot to know what your parts are going to need to handle.