Newbie- How do I bypass Dewalt 36V internal fuse?

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Markc
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Newbie- How do I bypass Dewalt 36V internal fuse?

I was told that there is a way to bypass the internal fuse of the 36V battery. If the info is on the board, I just cant find it.

I am hoping that this will solve my blinky issue, and that the overall BMS is still functional..

Thanks-

reikiman
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Re: Newbie- How do I bypass Dewalt 36V internal fuse?

"Blinky light issue" .. please say more? I assume you mean the behavior where you put a pack in the charger and the charger refuses to charge and just blinks the lights. I think (am not sure) this happens when the pack is below a cutoff voltage where the charger believes there's something wrong with the pack.

Anyway.. I don't know of a way to specifically bypass the fuse. However it's pretty simple to bypass the BMS unit for discharge.

You have to get a set of TORX tools - and specifically the ones that have a dimple in the face of the tool, since the screws used on the DeWalt packs have a matching nipple inside the screwhead. These TORX tools are sold e.g. at auto parts places because they're sometimes required for audio system install (so I was told).

Bypassing the BMS is simply a matter of a) opening the pack (using the TORX tools to unscrew the screws holding it together), 2) soldering a pair of leads to the + and - poles of the pack, c) bringing those leads outside the pack, 4) building a connector on the ends of the leads, e) closing the pack back up. With that setup you will bypass the BMS for discharge and can use the BMS for charging.

Markc
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Re: Newbie- How do I bypass Dewalt 36V internal fuse?

Thanks David-

Yes, I was referring to the charger blinking. I understand that this will bypass the BMS for discharge,(and I have seen the thread with the great photos illustrating this) but will that solve the issue of the charger recognizing it as something wrong, as it would still be the same connection when I try to charge it?

I saw the thread where you had to charge individual cells, would I need to bring them up to a certain point before the charger would accept the battery again?

reikiman
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Re: Newbie- How do I bypass Dewalt 36V internal fuse?

It's been a few months since I last played with dewalt batteries

but will that solve the issue of the charger recognizing it as something wrong...would I need to bring them up to a certain point before the charger would accept the battery again?

I believe that you would need to do so. And if you found my kaboom post you will have seen the results of incorrectly charging these cells too quickly ;-) ... Bypassing the BMS means that you can discharge the cells below the thresholds. The charger is (as I recall) looking to see if it's below thresholds and refusing to do anything if the pack smells wrong to it. I did at least once individually charge cells and get a pack to switch from causing the charger to blink to do the charge.

Jeffkay
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Re: Newbie- How do I bypass Dewalt 36V internal fuse?

Yes, it might not be the fuse, unless you have proved there is NO voltage coming from the pack...

Here, from elsewhere on the web, is the trick way to bypass forever the fuse (the fuse is not "out in the open"--so why you could not find it!): "There is an indention in the plastic next to the negative pin. I used a small drill and opened it up all the way through. The wire can then be run from the battery tab, under the module and up through this hole. Then simply solder it to the side of the outer most negative connector. Was really easy after I figured out how to do it. Just drill one hole, and do some soldering..."

I did not independently try the above but it seems correct.
Jeff K. "Deep Cycle"

Markc
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Re: Newbie- How do I bypass Dewalt 36V internal fuse?

Thanks to you both. Jeff, you say from "elsewhere on the web". Is there a site that has any pictures of this being done? I am a bit thick in the head when it comes to these things, but I am so very interested in learning it. I will verify that I there is no voltage coming from the batteries, thats right two brand new batteries! they got fouled up when I connected everything to flashlight conversions. No sound, no smell, no hot wires, simply nothing when I turned on the power switch. They were both fully charged when I connected them. I tried putting them back on the charger, and immediately both went to the blinking light.

So to be clear, if there is voltage the problem is the BMS, thus my only solution is replacing it?

I have read much about instantly frying the BMS, I am just hoping that this is not the case. If there are any threads or pages with pictures (kind of like a Denny's menu :)) it would help me a lot. Otherwise I will continue my ritual of staring at the battery for about an hour, then walking around it three times, then trying what I think is right based on reading suggestions. This technique has about a 30% success rate for me!

mn_aerorider1
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Re: Newbie- How do I bypass Dewalt 36V internal fuse?

The most likely cause of your blinking light is not a fuse, but is probably a low cell. I have repaired a Dewalt pack with a low cell, by opening it carefully using the security torx screw driver, and then accessing the particular cell that was low via the two small 5 pin connectors inside the pack. I first disconnected the 5 pin connectors that lead from the Battery Management System (BMS) Module, located in the lid of the pack, to the battery pack. I then used two little 5 wire harnesses I have made from some 5 pin female connectors that I bought from a Taiwan manufacture that are identical to the white 5 pin male connectors coming from the BMS module. (I still have a bunch of these connectors if you are interested in trying this.) Using these wire harnesses, I was able to access each individual cell and test which one was low, and then also charge the low cell above the required 2.5 volts using a couple of D cells in series. The blinking then stopped.

You might be able to probe the individual cell access pins by using a couple of small female connector pins pulled out of a non-matching connector, but you face a great risk of shorting between the pins and melting the pins, along with the wires leading to the cells.

Another, perhaps better way to access an individual cell, if you can't build a harness or probe the connector, is to carefully lift the 10 cell string of white battery cells and the two long black plastic end-caps out of the yellow Dewalt pack case, by carefully prying on the black plastic ends little by little with a screwdriver. It is all just a pressed fit. Don't worry, it is easy to reassemble the end caps onto the cells and put them back in when you are done. These two black end-caps are just pressed onto the ends of the cells with conductive springs in between. Carefully move the black end-caps out of the way and you can then probe the top and bottom of each cell and see which one is too low, and then charge the low cell using a power supply or some C or D cells.

I hope that helps.

Good Luck!

Brian

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