Thanks Mike for the recommendation.
My blade on my B&D MM675 measures 17.5" even though the specs say 18"
cutting path. Most of the lower voltage electrics have a 14" blade.
The smaller mower means more passes. Something to think about.
On 4/28/2014 3:45 PM, Michael Ross wrote:
I have another battery from these people that seems just fine (after taking
it apart to see inside)
http://www.aliexpress.com/store/product/24V-40AH-LiFePO4-Battery-Pack-Electric-Bicycle-electric-Scooter-bicycle-E-Bike-Lithium-Ion-Long-life/328001_771068114.html
This one is 24V 40Ah LFP and weighs 9kg. $500 including shipping BMS and
charger. 3 to 7 day delivery and the met that. These that 18650 cells with
welded straps for conducting the juice.
I think I will try to get a used 24V B&D instead of reworking my old bottom
of the line MTD.
I think my wife would love to have an electric mower. She hates asking me
to start them for her. It would be nice not having all the oil checking
and filling, And as the current mower works - the rod knocking and
smoking. We have an acre of mostly flat yard - 40Ah would go a long ways
and the charge time is about 2 hours.
On Mon, Apr 28, 2014 at 3:25 PM, Peter Eckhoff <[email protected]> wrote:
Hello Mike,
I'll second what Cal is saying below. To get the nut off, you have to
place a wrench on the nut and "impact" it until the nut loosens. I would
**not** use a compressed air impactor tool. I use my fist. Be careful
because everything is free wheeling. If you leave your knuckles in the
path of the blade, your knuckles are going to get whacked. There is no
other place to place another wrench unless you weld a nut to the top of the
motor shaft.
Like Cal, I keep a set of several "small plastic blade insulators" on hand
which is how they are described in the User's Manual. The word "insulator"
may seem like a misnomer but it is to "insulate" the shock of hitting a
rock from damaging the armature.
I converted a corded B&D to cordless. It uses 9 - 5 amphr 12 volt LA AGMs
to power the mower. It is enough to do a 7K square foot lawn. What used
to take me 1.5 hours to do when corded, now takes about 45 minutes.
I use a 1.3 amphr AGM for the tripping a small contactor. This battery
goes down faster than the pack. I would use about a 2 amphr battery for
each hour the contactors are tripped. That should give you plenty of
cushion.
I wrote a two part article for the Electric Auto Association's Current
Events magazine. I have the submittals in PDF format. The B&D motors are
DC universal motors that operate at 120 volts. The corded version has a
full rectifier bridge on a little heat sink. It was mainly a rewiring job
to bypass the rectifier.
I think the AGMs are the wrong type of battery for this project. Normally,
when not cutting the lawn, the motor consumes about 4 amps. When cutting
thick grass, the motor consumes about 8 amps. It can spike to 10 amps in
real thick grass or when the mower clogs up in thick grass.
I have been contemplating upgrading this mower to Lithium. A set of 40 -
3.2 volt 10 amphr would be about right for an hour's worth of cutting and
still have some reserve. I saw an ad for Shorai 12Volt 12 Amphr batteries
for $117 each and they weigh about 1.7 pounds. My 5.0 amphr batteries
weigh 3.5 pounds each for an added weight (starter + pack support +
contactor) of 35 pounds onto a mower that weighs 47 pounds for a total of
around 82 pounds. This is about the weight of an ICE push mower. Twelve
Shorai batteries would be around 20 pounds. The mower would be lighter and
so would your wallet of $1400 plus shipping.
I have thought about purchasing 4 - 100 amphr CALB batteries and then use
a converter to step up the voltage to 120 volts. At an efficiency of 85%,
the amphrs to the motor would be about 8.5. I am not sure if a converter
could handle that much amperage. I was going to do some more homework
before asking the experts here. Four CALB batteries would be about 600
dollars and a converter would run in the lower several hundreds. The
savings would be substantial but I am not sure if the electronics would
handle the load.
The other thought would be to run the 4 CALBs into an inverter and leave
the rectifier bridge intact. The inefficiency of the inverter plus the
inefficiency of the rectifier bridge would likely sap the pack of a lot of
useful energy. I think this would be a nonstarter.
I know of someone using a self contained electric mower. You might want
to shoot him an email at theadm *A*T* AOL. If you are in the RTP area, we
are both "local".
Everyone else I see running an electric mower are running with a cord. If
you want me to, I will ask my neighbors their brand and opinions.
On 4/28/2014 1:27 PM, Cal Frye wrote:
I'm on my second Black and Decker push mower, corded type. I have a
small lawn, so avoiding running over the cord is not a major problem. I
won't advise on motor or batteries, but I can say B&D has a plastic shim
in the stack of washers holding the blade to the motor shaft. Said shim
has raised edges which grip either side of the blade, and an opposing
pair of edges which grip in turn a keyed, square washer above the blade.
This square washer is driven by the motor, and the blade is driven by
the plastic shim. Hit too hard an obstacle, and the plastic edges shear
off and the blade rotates freely.
This is effective, but is also a wear point, and I've learned to buy the
shims by the half-dozen. My eyes don't always find the rocks in the yard
before the blade does :-(
Best regards,
-- Cal Frye, www.calfrye.com
/Be an Internet Sceptic/ Stop. Think. Connect.
www.stopthinkconnect.org - Be at least as safe on the
Internet as you are crossing the street!
"I sincerely believe that banking establishments are more dangerous than
standing armies." -- Thomas Jefferson, letter to John Taylor.
Michael Ross <mailto:[email protected]>
April 28, 2014 12:58 PM
I have an old simple ICE push mower, that might be worth converting.
...
What about the shock of the blade hitting something nearly immobile? That
is a lot of shock that small engines are able to handle - special
consideration in the regard with electric motors?
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