Upgrading 24V Homelite Mower to 48V

[joshseitz]

Starting to think about spring mowing here in the NW. I have a 24V Homelite UT13122 mower with dead SLAs and a missing charger. I also have a 4 year old Ping 48V 20Ah pack that's collecting dust in my garage. From what I've read, this mower can't handle a doubling of voltage, so I figured I'd explore replacing the motor with one that can.

I haven't had the chance to measure the motor housing or shaft diameter yet, so I thought I'd throw it out there to see if anyone has any first hand experience with this kind of conversion. My yard is small and the grass pretty easy to mow, so I'm not too worried about current spikes. Nonetheless, the Ping isn't good for much beyond 1.5C, so I don't want to destroy it since I don't plan on using a controller to manage current. Also curious if the original switch will be up to the task. Below are some photos of the same mower I found on the web.




Any experience/advice is appreciated as always!

 

[amberwolf]

Alternately you could reconfigure the Ping to be a 24V, taking the "top" half of it and disconnecting it's serial connection from the other half, and all it's parallel connections off the BMS, then connecting those parallel connections to the remaining "bottom" half instead, and a new main + and - connection from it's ends to the + and - connections of the "bottom" half.

THen you can look in some of the Ping repair / configuration threads about how to alter the BMS to work with less cells (AFAICR that's pretty easy but I don't know the details).

 

[dnmun]

i have a lifepo4 8S BMS too if you wanna do that and i think i still have a 24V lifepo4 charger.

then you could use the battery in parallel with your lead acid pack and then both would last longer.

the problem will be the motor. it is brushed so the heat from the sparking at 60V of the ping will burn the brushes up in a few seconds imo.

the brushes on mine were shooting sparks like roman candles on 24V so i cannot imagine how much it would be at 48V of lifepo4.

 

[nechaus]

iv had two of these mowers..

It cannot be converted to 48 volts, I have tried 36 volts and its pretty dangerous and starts to creates plasma @ the brushes.. On one of mine, the commutator blew into pieces.


If you want to give it more power, Id suggest 7s, Mine fried @ 10s
Not even sure if 7s would be safe for long term use.. Its a pretty weak motor, but better than many of the other e mower out there for the age.
Perhaps run 7s and use a speed controller..

 

[dogman dan]

7s should work fine on that mower, Lipo I mean. 8s for lifepo4 should work good, possibly 9s.

Just going to lithium will make a huge difference, especially if you use a non saggy type like Hobby king 20c packs, in about 10-15 ah. Not bogging down so much due to sag will really help when you hit the thick grass, and of course, losing about 20 pounds of weight from the mower will make it push like an empty baby buggy.

If you do change motors, be aware that you don't want a hugely higher blade speed. You don't need rocks thrown so hard they punch holes in brick walls on your house, or clear the fence and hit a neighbor. Nor do you want to throw the tip off a worn blade. If you could find a higher voltage mower on the used market, great. Or a replacement motor from a similar mower. So you get the right blade speed at 48v.

What you want for your existing motor, is just solid not too saggy 28-30v under the heavy load, so the blade keeps cutting nice when you hit the thick grass. For me, with my nearly identical B&D 24v mower, 7s hobby king packs is ideal. I use a battery for a few years on the bike, then retire it to it's last season running the mower. By then I may be cutting apart packs with a puffy cell, and just do whatever I have to, to result in a 7s pack for mower use. So it doesn't matter if I started out with 4s,5s,or 6s packs.

If you will buy new stuff, one easy way is to just get 2 4s packs, and a couple 3s packs. Or a 5s-2s, whatever adds up to 7

 

[joshseitz]

Thanks for all of the advice. I may keep an eye out for a dead 48V mower on craigslist, as I really like the idea of the power of the 48V battery and not having to break apart the pack and BMS.

 

[joshseitz]

Think I could get away with running one of these 40V Kobalts on my 48V ping: http://portland.craigslist.org/mlt/grd/4808755538.html

Or this perhaps: http://www.homedepot.com/p/Ryobi-16-in-40-Volt-Lithium-ion-Cordless-Walk-Behind-Lawn-Mower-Battery-and-Charger-Not-Included-RY40100A/203362215?cm_mmc=Shopping%7cBase&gclid=CJDBlKLXiMMCFVKPfgodcBoALw&gclsrc=aw.ds

 

[dogman dan]

Yes one of those is what you are looking for. Perhaps you can get a replacement motor for one? Then convert the mower to 48v?

 

[mateusleo]

Have you thought about using a dc dc converter? http://www.aliexpress.com/item/DC-D...-dc-to-dc-converter-module-Dc/1109337491.html Those are used in golf carts i belive, they are easy setup and can handle 48v in and 24v 10a out. Seems to fit your needs...

 

[amberwolf]

PRoblme is the motor's startup surge current could be hundreds of amps for an instant, and it would probably shutdown the DC-DC if it has protection, or fry it if it doens't. :/

 

[dogman dan]

Re reading, just chop up that ping and make it into a stiff 24v pack if you have a way to charge it. You could even use a cheap sla scooter charger if you must. Balancing it manually won't be that hard to do once you add 8s JST plugs to the old balance wires.

 

[joshseitz]

So I picked up a Kobalt 40V mower sans battery and charger on Craigslist for $40 yesterday. I am going to see if I can make it work with my big ol' Ping 48V/20Ah pack that I just don't have much of a use for on my bike.

For the time being, I think I'm just going to strap the Ping to the rear of the plastic motor housing. It seems secure enough and will allow me to test it out without chopping things up.



View attachment 5



My primary question concerns battery wiring. The existing battery dock clearly identifies positive and negative, but there is a third (blue) cable that runs from the battery dock to a small box that looks like a small controller(?) before hitting the motor.

Any idea what this blue cable is and how (or if) it needs to be wired? The original batteries are removable so no charging took place in the mower itself.

thanks.

 

[dogman dan]

Dunno what that stuff is, but it looks a bit like fets attached to a heat sink. Might be on off tied to the original lithium pack? Like maybe the pack gets hot, mower shuts off? I can't picture controller, not like you adjust the speed like a gas mower. Blade brake?

Jack the ping wires straight to the motor ought to work fine. The plug becomes the on off switch. Careful about clearing out the chute, that blade will keep spinning a long time if you hotwire the motor. No blade brake.

 

[dnmun]

no way to know since no wiring is visible to determine where the leads go.

it looks like the same motor used in the B&D battery powered mower.

 

[joshseitz]

So as it happens the 40V Kobalt actually uses a 24V motor. The little black box must serve as a step-down transformer I suppose? For kicks I hooked-up the 48V ping directly to the 24V motor and it was apparent that it wouldn't last at this voltage. Sparks were flying from the motor, and there was a pop in the Ping's BMS just before I let the smoke out. Not sure if I killed it or not - haven't re-tested it yet.

It looks like my best bet is an 6S pack. With 2 such packs, I can have a backup light-weight 12S pack for my 48V bafang crank drive. Anyone in the market for a 4 year old Ping with a questionable BMS?

 

[amberwolf]

Anyone in the market for a 4 year old Ping with a questionable BMS?

rewire it into two 24v halves, and parallel them. should work ok on the mower that way.

bms can be fixed if it popped, would just be the fets most likely. dnmun would know for sure how to help you fix it.