cordless electric mower question

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sir_loin
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cordless electric mower question

Hey howdy. forum noob and electronics noob here. just looking for some help.

I recently bought a used B&D cordless mower. it's a 12 volt. Not bad, but a little under powered (it was 20 bucks, how do i say no?)

I'm wondering what it would take to beef it up to 24 or even 36. I assume it's not as simple as just dropping 36 volts worth of batteries in.

Or should I just buy a new 12v deep cycle battery and use it as is?

thanks all!

dogman
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Re: cordless electric mower question

It could be just that simple. It just depends on how complicated the electronics on it are. If it has a simple brushed motor in it, and a simple on off switch to turn it on, it might work fine at 24v, as long as you don't run it though enough tall grass to overheat the motor. If it is more sophisticated, with a brushless motor and controller, then it might need a 24v controller to upgrade it. A second battery in paralell though, would be very likely to improve perfomance by reducing the voltage sag without changing the voltage.

Be the pack leader.
36 volt sla schwinn beach cruiser
36 volt lifepo4 mongoose mtb
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reikiman
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Re: cordless electric mower question

And since you're an electronics newby (as you say) you might appreciate a decoder ring to what dogman just said.

"simple brushed motor" ... So far as I know the simplest way to tell whether you have a brushed versus brushless motor is through counting the number of wires going to the motor. 2 wires = brushed, more = brushless

"controller" ... Most electric vehicles have a box that sits between the throttle, battery pack, and motor. It varies the power to the motor based on the throttle. If the controls are just an on-off switch it's possible there's no controller. If there is more to the controls there may be a controller. Trace the wires to see what's there.

Aerowhatt
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Re: cordless electric mower question

It's a safe bet that it's a simple brush type motor (In my opinion a good thing). Most likely just a switch between the battery and motor. 24 volts might be OK but 36 would definately be dangerous. As you raise the voltage you will be raising the blade and motor RPM's. Go to far spinning the thing faster and it will come apart. It may just be "underpowered" because the battery is old and not kicking out power fast enough. I think the safest thing to do would be to try a high output 12 volt battery in good condition. That alone may pep it up enough to be adequate.

Cordless mowers are great. I've used electric mowers since the 1970's. Recently I finally retired my home converted cordless and bought an Earthwise 24 volt mower to replace it. The thing is great, so much easier quieter and better than a gasoline powered mower. Since mine is recharged with wind power, I have the "greenest" lawn in the neighborhood whether it looks it or not.

Aerowhatt

sir_loin
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Re: cordless electric mower question

awesome, well I can tell you that there's no controler. it's got an on and off setting, like most electric motors. whether or not it's brushless......i'm gonna have to double check. but basically, if it's brushed, I just drop a new battery in (24v if i can find one) and away i go??

or...someone mentioned two 12's in parallel for a longer more constant voltage....how do i go about wiring that up?

Someone also mentioned the danger of high voltage and I agree, after thinking about messing around with toys as a child i remember what happened when we tried to pony up a few extra batteries to a little car. while it just drove like hell, the spinning blades could pose a problem.
many thanks!!

garygid
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Re: cordless electric mower question

These questions are like many others that ignore the safety aspects of attempting to use things beyond their design limits:

1. I have a kitchen blender but I want it to "do more" (vague use), so I am planning to plug it into the 240 volt electric dryer circuit. What plug should I buy?

2. I just blew the fuse while using my electric stove, which has worked well for years. Should I use a Philips or a Flat-blade screwdriver to short across the fuse to test it?

3. I think my 37 year old lawn mower (driven by a 12 volt SLA) has a blade was designed for 4000 rpm use but the mower is starting to vibrate. To fix that, I added a 40-volt battery. I am a nubie, so I cannot post the Hi-Def video of how the new battery caused the motor to explode, the blade to fly apart (broke at a work-fracture stress crack), and what the ejected blade did to my ankle (removed my foot). After getting out of the hospital, I could not find a replacement blade, so I hammer-welded the blade back together. Where can I buy an exact-replacement motor (cheap), and a 80-volt battery pack with BMS and LVC that would fit?

Thanks.

Moral: Things are usually replaced with money. Safety should be considered, at least if you are worth more than the sum of your (remaining) body parts.

Cheers, Gary
XM-5000Li, wired for cell voltage measuring and logging.

dogman
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Re: cordless electric mower question

Ok call me Tim Taylor. The thing is mostl likey best left at 12v. But a larger supply of 12v power will likely help, especially if the battery is old. Chances are, it's a 12v 12amp hour battrery, so maybe a larger size could be bought from a place that sells wheelchair batteries. Mabye, if it will fit, an 18 amp hour battery would run longer at good strength. And yeah, if it really vibrates, the blade needs replacing, or it may have a bent shaft, and would be dangerous for sure. I sorta doubt that it spins very fast with 12v though, and I bet a gas mower spins it's blade a lot faster. Even the corded electric mowers I've used are pretty anemic compared to gas. But if the lawn is not too huge that's fine.

Be the pack leader.
36 volt sla schwinn beach cruiser
36 volt lifepo4 mongoose mtb
24 volt sla + nicad EV Global

sir_loin
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Re: cordless electric mower question

Well garygid, despite being a bit facetious, the point is made. However i'm not talking about spinning the thing up to 10000 rpm. as i said, getting longer life out of 12v is my preferred option. it's a great little mower, just cant quite handle the whole lawn. and where these things retail for 299 new for a crappy one, i figured 100 for a used one wasn't so bad. (20 for the mower, est. 80 for the battery) now if i could add a little more power to it (18 or 24v) without spinning it up too much, it'll still be safe. it's got a metal deck (inside the plastic casing) the blade is pretty much brand new) yes obviously if i put 48v to it, i'm asking for a potential amputation. however, i've had the same thing happen with my trusty old gas mower without doing anything to it. the blade simply failed. had it been 1/4" lower, i would have caught it right accross the achilles tendon, instead of it sticking into the deck.

having said all that, if it's just as simple as putting a 18 amp hour battery in to replace the old 12(i'm assuming) amp hour battery. then that's what i'm going to do! or put an 18v in for a touch more power, we'll weigh the costs.

the other question i have that should probably be addressed is the charger that came with it. I assume the 12v 18a/h battery won't require a different charger, but what about an 18 or 24? It would stand to reason that it might need a different charger, one that's made for 18 or 24 v batteries..no??

sixpax2k9
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Re: cordless electric mower question

That would be very correct. Most 12V chargers put out about 13.5V. If you wanted to go to 18V or 24V you would either need to buy a 18V or 24V charger or you could use 2 chargers(though it would be more complicated to use 2) Walmart sells a nice schumacher 6/12V charger. Depending on what you are looking to spend you could also consider a 16V lithium battery pack. Though it is more expensive, the slight 4V jump would most likely cause no problems with the mowers parts, it would make it lighter, and would last longer than SLA batteries.

If you want to play it on the safe side and it works fine as is and you just need it to last a little longer to finish the yard then YES by all means just go to a higher AmpHour 12V battery..

Dave ; Tennessee
XB-600.

garygid
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Re: cordless electric mower question

Well, using five LiFePO4 cells to get about 3.3 x 5 = 16.5 volts, and putting in 50% (or more) capacity (Amp-Hours) would probably do what you want, with less risk.

The 20 Ah ThunderSky cells (about $40 each) from Elite Power Solutions might be good. The 10 Ah PSI cells (very good cells, but more expensive, with 2 in parallel as one "cell", and 5 "cells" => need to buy 10 PSI cells) from AndyH might be excellent, but perhaps to many $$.

If necessary, charge each cell with one of the $12 single-cell (2 amp) chargers from VoltPfreaks? Better, buy 5 chargers and charge all the cells at once.

With any battery, avoiding over-discharging is critical for longer cell life. Thus, an LVC (Low Voltage Control) mechanism or plan of some sort is VERY important. However, it might be as simple as a $2 voltmeter from Harbor Freight showing the Pack voltage. When it gets down to perhaps 2.9 volts per cell (14.5 volts for the Pack), quit and recharge.

Is there a fuse in the circuit, or only the ON/OFF switch, the motor, and the battery pack?

Of course dropping in a new larger-capacity "12-volt" cell is easier and probably cheaper.

Cheers, Gary
XM-5000Li, wired for cell voltage measuring and logging.

Boukman
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Re: cordless electric mower question

I don't want to interrupt everybody in their track, but the only cordless lawn mower I know that Black & Decker produces is a 24V model. Here it is : http://blackanddecker.com/ProductGuide/Product-Details.aspx?ProductID=16345

Black & Decker have basically been producing the same model for many many years now... Maybe sir_loin should have given us some more precise specs to his lawn mower, or given us a link to the specs on the B&D website before we go into a debate about what is feasible or not...

sir_loin
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Re: cordless electric mower question

I don't want to interrupt everybody in their track, but the only cordless lawn mower I know that Black & Decker produces is a 24V model. Here it is : http://blackanddecker.com/ProductGuide/Product-Details.aspx?ProductID=16345

Black & Decker have basically been producing the same model for many many years now... Maybe sir_loin should have given us some more precise specs to his lawn mower, or given us a link to the specs on the B&D website before we go into a debate about what is feasible or not...

on the contrary, B&D has not been producing the same model, mine is a 12 volt, not 24, and it's pretty old, i'm guessing 8 to 10 years, though possibly older.
I can't link to the B&D website for the specs, because I can't find this mower ANYWHERE online.
furthermore, the newer model is actually considered inferior to it's predecessors. due to cost cutting measures, the components have all been lightened (weakened), and the batteries aren't really a hell of a lot better than what I have now.

so AS I said before. I'm going to look at a 12v battery, with a much higher amp hour rating. I have a few options. we have an "everything batteries" store here in sudbury that should be able to provide something. Also there's a wheelchair repair and supply store that might have something with a good lifespan. and then there's the whole lithium ion option. just depends on how much i'm willing to dump on a battery.

Thanks to those who were able to point me in the right direction.

Oh and I finally got in touch with my uncle (35 years in electronics) a good thing I chose against higher voltage. he's pretty well convinced i would have cooked the mower. apparently it has a 12 v battery, because it's got a 12 v motor.

fancy that

sixpax2k9
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Re: cordless electric mower question

Oh and I finally got in touch with my uncle (35 years in electronics) a good thing I chose against higher voltage. he's pretty well convinced i would have cooked the mower. apparently it has a 12 v battery, because it's got a 12 v motor.

fancy that

Well there are MANY people on here, myself included, that are running motors over the "rated" Voltage. In my experience almost any motor can be slightly over volted with a few exceptions. I dont know what size the battery is but you might want to search on here for "12V battery" as there are quite a few links with good priced batteries from 12ah to 20ah 12V.

If you dont want to chance over volting the motor i completely understand. If it is working fine just up the amp hours and go on your merry way!!!!! cheers to ya!!!!

Dave ; Tennessee
XB-600.

sir_loin
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Re: cordless electric mower question

All I'm curious about now is charging the battery. will the built in charging setup (I plug a transformer that came with it into the back of the mower) be able to charge a different battery other than what came with the mower initially????

Or should I invest in a cheap battery charger??

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