Thursday, November 12, 2009

Fixing a problem (June 2009)

Table of Contents

Important note: if you have a question to ask, please ask it at Lawn Mower Forum, either in the Black & Decker area or the Electric & Battery Operated area at that website. I apologize for being unable to handle individual requests for help posted on this blog or sent by email.
The Story

Last spring, my CMM1000 mower developed a problem where it would simply stop running after 5 or 10 minutes.  It would restart again after a minute, but then only run a few minutes before stopping again.

The problem turned out to be a faulty circuit breaker, which is supposed to cut the motor off when the current exceeds 40 Amps but was actually tripping at a lower current.  At first I misdiagnosed the problem as either a worn out battery or bad switch contacts.  At a loss as to what the cause was, an internet search led me to other people with the same problem ... and more importantly to somebody who had fixed it by replacing the breaker.  And so I extend a hearty thank you to "rothompsons", whoever you are, for posting the solution at

After ordering a new breaker for $19 ($12 part + $7 shipping) from, the mower was up and running again! In the intervening month it took to find and fix the problem, I used our trusty manual push-reel mower to cut our grass.

By the way, my original breaker lasted 3 years, and rothompsons's lasted 2-1/2.  Another person did report that their mower was 6 years old when they first encountered the problem.  At any rate, you can expect your breaker to fail eventually.  You'll know it's the breaker if your mower stops, and can be restarted only after you hear a "click" about 30-60 seconds later.  The click is the automatic reset switch inside the breaker, after it has cooled down enogh to close the circuit again.

Repair details

If you need to replace your circuit breaker, here is where you can find it on the mower's Main Circuit Board:

Main circuit board, showing location of circuit breaker.

The breaker is in series with the main switch, and when tripped breaks the connection from the battery to the motor.  It is attached to the main circuit board using nylon-insert lock nuts:

Main circuit board, showing electrical path between Battery(+) and Motor(+) terminals.

A view of the brand new circuit breaker, part # 5140004-81 from

The brand new circuit breaker (includes nuts and lockwashers) from

Request of readers:

And finally, here is a request of anyone reading this blog.  If you can find these circuit breakers for cheaper than the $12 I paid for this one, I would love to hear about it!  Please note, it is manufactured by Cooper Bussman, and is their Shortstop series 120 circuit breaker.  It should be rated for:
  • 24 V
  • 40 A
  • Must be of the automatic reset, thermal cycling type, not the manual rest type.
I have found a 12V version for under $4 at, but so far not a 24V version.  It would be nice to order a few of these to have in stock.


  1. 40A 24vdc auto reset circuit breaker is a cooper bussman ATSCB40. I'd prefer not to spend $12 either. Looks like we have choices.

    Here's a few links to order online:
    BEST DEAL I found $4.23 shipped at

    $5 at

    $3.34 at

    11.25 factory dewalt item 100

    Hope this helps.

    Hope this helps.

  2. You can always go to where these original parts were bought from the photos. has parts and accessories from over 40 name brands, so I'm sure you will be able to find a circuit breaker to your liking.

  3. I'm having a hard time figuring out if the ATSCB40 at sears and jcm industries are 24V? Cooper Bussman makes a 12V and 24V version and the manufacturer's part number starts with 12? where the ? defines 12 or 24 volt and the reset characteristic of the breaker. This mower user a 124B40. Ted L. can you confirm the sites listed above are selling the 24V version?


  4. If you go here ( ), you can find this type circuit breaker for $2.60. It is rated 6-24 volt, 40 amp and type 1 (auto reset).


  5. I've been trying to get a CB from Light Exports for almost a month now. They keep saying it shipped, but can't give me a tracking number. As of today, 4 weeks, still no part and they are not answering their phone or email now.

  6. After escalating my complaint of LightExport through PayPal they finally shipped my part, for the third time. This time they actually gave me a tracking number. It took over a month, but I finally got the part. I installed the circuit breaker and it works like a champ. I was able to cut my entire lawn without any interruptions.

  7. Are this type of circuit breakers polarized? Mine (for CMM1200) has a perpendicular mount. I found, that has the identical description (except for minor differences in dimensions) as the mentioned by Anonymous in summer 2011. The CB130-40 has two silver-colored terminals though, while the CB125-40 (and the one on my mower) has one silver terminal, one bronze. Does the colors signify something? Are the two breakers (CB125-40 and CB130-40) fundamentally different, despite of their identical specs (except for the mounting bracket and dimensions)?


  8. Without seeing your breaker - look at the bottom side - where the studs are. See if it's labeled "BAT" and "AUX". If so, then just like it says - BAT to bat+ terminal and AUX to the circuit board.

    FWIW - I bought my braker(s) from for $2.27/ea. Shipping was $9.50 so I bought 3 breakers for ~$16. I ran it for a couple of weeks with a 12v rated 40a breaker from the auto parts store until these arrived - worked just fine.

  9. Thanks, Anon, does seems to offer the best deal for bracketed breakers, I might by a few more from there for the future. At the beginning of May I found a bracketed Type 1/24V/40A breaker here: with the bi-colored terminals and decided to give it a try. It's $6.99 each, with $6.84 shipping (on, it's now $15, Plus $10+ shipping). It does have the "BAT" and "AUX" marking. Last night I put it in, and it fixed my mower's stop-and-go problem.

    The WindyNation site has a nice explanation about how the circuit breaker works - if the current exceeds 40amps, the breaker heats up, the connection is broken until it cools down. With the old breaker, the stopping seemed more likely to happen after the mower had been running for a while. I remember that "power equals to voltage multiplied current", so a breaker is more likely to trip if the voltage from the battery is lower. Does that make sense? I wonder if this type of circuit breakers have a fixed lifespan, i.e. "tripping point stays at 40 +/- 2amps for the first 200 trips; after that the error margin enlarges (to, say, +/- 7 amps)". In that case the problem with breakers is not really a "design flaw" of the mower, but something to be expected because the circuit breaker was exhausted, as the battery eventually would be. In that case, I wonder if an "exhausted" circuit breaker always trips at a lower amperage, or if it's also possible to trip at a higher amperage. The latter would be much worse. So it might be a good idea to replace the circuit breaker, say, every 3 years? I'm just speculating here based on vaguely-recalled high school physics. Would like to hear from others knowledgeable in this.

    My mower is 5 years old, and the stop-and-go problem began late last season. I never heard a "click" though. I thought it was the battery, which would have been a bit disappointing but not totally unexpected. This blog is great. Much thanks to Mark and the other commentators!

  10. I think Ohm's law applies here. And since Current(amps) = Voltage divided by Resistance, and assuming resistance in this case remains constant, then as voltage drops current also drops. I could be wrong, though!

    I say if it ain't broke don't fix it. I would assume that the breakers are designed so that as they tire they trip @ lower amperage.

    My mower is abt 10 yrs old and the breaker just failed. I was mowing along on a near full charge and the thing just quit. In it's life it only tripped once or twice, but I'm sure it's heating up every time the mower is used, just not to the point of tripping.

    On the brackets - I just trimmed the ears off - no biggie. And remember, if you buy 500+ breakers from DelCity they drop to the ridiculously low price of $1.78!!

  11. Thanks, Anon. I mowed the lawn a 2nd time a few days ago since replacing the breaker, and it worked fine. One thing I noticed: when the old breaker cut the motor off, I could restart it within about 30 seconds. When I go through thick grass with the new breaker and the motor gets shut off, it takes much longer to resume the connection - probably 2 minutes. I suppose this is just due to normal variance among different breakers.

    My new breaker has an "ear" (bracket) on each side. The original breaker had a bracket on one side, the other, ear-less side lay flat against the inside wall of the mower. I rotated the new breaker 90 degrees and mounted one side of the bracket to the mounting post, and left the other side of the bracket out in the open.

  12. Glad I found this post. I, too, replaced the battery set, thinking that was the problem. I was online today, getting ready to bypass the circuits with a 24V chargers, a main switch, and a safety brake relay. I think I'll try this, first.

    I also think I'll use the old batteries for power backup. :)

  13. Important note:

    If you have a question to ask, please ask it at Lawn Mower Forum, either in the Black & Decker area or the Electric & Battery Operated area at that website. I apologize for being unable to handle individual requests for help posted on this blog or sent by email.

    Link to Lawn Mower Forum's main page:

    From there you'll find the Black & Decker section (under "Brand Specific Forums" and the Electric & Battery Operated section.

    Best regards,



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