Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
BMS problem (need second opinion)
A motor speed controller would let you "soft-start" the motor too, avoiding big surges at start-up....
ajw22 and Ibiza like this post
Running off solar, DIY & electronics fan :-)
(08-28-2020, 01:53 AM)ajw22 Wrote: Just going by the "marketing" values stated in the manual:
24V * 10Ah SLA battery => 240Wh energy
runtime of 50(~60)min => 288W or 12A motor draw

The BMS has a continuous discharge current of 25A, and peak discharge of 60A. Peak is probably allowed for only a second or two.

A motor typically needs 2x ~ 3x the current during startup, and lawn mowers typically need several seconds to spin up the heavy blade.
So the likely situation is that the motor starts up drawing in the region of 25A~60A, but then the BMS cuts off after the time allowed for peak discharge is exceeded.

Second Daromer re clamp meter, but it might be difficult to get good accurate reading for startup current.

Possible solution besides a bigger BMS:  motor speed controller.
No actual experience, but something like this should do.  Might require additional cooling.

edit: Doh! simpler calculation:  10Ah battery / (50/60)h => 12A

Thank you for the suggestion. I have never worked with Motor speed controls but that does sound like it would work. 

Jeremy Fielding has some youtube videos on them, so I will have to do some research on how to set this up. 

This is a winter project (Canada) so I have 4 or 5 months to play with this before I would need it next spring. 

Delivery times from Aliexpress have been nasty as of late (2 to 3 months) with the COVID-19 so this could be a very slow process.
ajw22 likes this post
(08-27-2020, 02:51 AM)jonyjoe505 Wrote: I think your power ratings for your lawnmover might be wrong. 28.6 volts x 6 amps = 171.6 watts. The bms is 28.6 volts x 25 amps = 715 watts (but it peaks at 28.6 volts x 60 amps = 1716 watts). It can handle the peak but only for a few seconds.

171.6 watts seems too small for an electric lawnmover, when I google it mention anywhere from 900 to 1500 watts for most lawnmovers. If you have a dc wattmeter, you might be able to use that to get an accurate wattage for your lawnmover.
I finally looked at the motor on the lawnmower and it seems that is a GLOBE 70A5F motor - Not a large amp motor to say the least. I was not able to identify the exact model (There are 5 to choose from). The sticker on the motor does not have a lot of information other then it is a GLOBE 70A5F and is 24VDC.

From what I can make out from the spec sheets these motors have around a 1A rating (this is just a small 14" lawnmower). 

There is no motor control board on the system it is a direct connect from battery to motor with a switch for on-off operations. 

The other numbers on the sticker were 

globe 70A5F
I googled for "3610145-1 motor" & got lots of references to mower motors many seemed to be 40V/7A or so.
Eg a 24V one is likely to draw more current than a 40V one.

So I'm guessing a motor like this is going to draw at least 10A when running. No chance it'll be only 1A! Cutting grass is hard work....
The motor linked is for hobby models, eg remote control cars, etc
I'd be looking for a 30A motor controller to be sure.
Running off solar, DIY & electronics fan :-)

Forum Jump:

Users browsing this thread: 1 Guest(s)