Dewalt A123 BMS battery interface solution

[kfong]

I haven't finalized on the inductor. I still have a few to test out so the price might change depending on which I find is best. I’m just waiting to get them. The wire gauge should be chosen to match the current you will be flowing through them or thicker. The dewalt packs using the BMS can put out 20amps. Magnet wire works best, but not needed. I only use one inductor for the whole pack. It goes on the positive lead between the controller and the battery. It will need to be a big enough gauge to handle the current. You can use several inductors off of each battery bank if you want to reduce the wire gauge. I just wind wire around the toroids till it works. It just needs to be enough so spikes are small enough not to effect the BMS.

The caps and inductor will only help smooth out your voltage. They won’t increase it. Your batteries, are the ones not holding up under load. You need to increase the cell count or parallel more packs and be sure you are using heavy enough wire gauge so that you don't get losses from the wire. Chart on wire sizes, just follow "maximum amps for chassis wiring"
http://www.powerstream.com/Wire_Size.htm

kfong what inductor are you using to stop the spikes that you will sell for $10 is it off the shelf or hand made ?

What gauge wire are you using i.e what current does it handle. dewalts packs are rated to 15 amps output or 25 ? what gauge suits that?

The inductors i made in the past used 14 gauge enamel coated magent wire that i managed to turn 29 turns around a 38 mm od ferrite toroid.

i need to make some more inductors as i am making more packs and and wondering if i went over kill on the 14 gauge wire for each 36v dewalt pack. what wire diamter are you using ?

As the for the spikes i dont have any at all so it works, but i would prefer a slightly higher inductor value becuase my packs i am actuly using them at the 26v setting and not full duty cycle 34 volts. i can see on my osciciscolpe that the volatga is not flat and spikes up and down under load from 26 to 34. Packs do not cut out though and work perfectly fine its just what i see on the osciscope that i feel is a problem ? to fix it last time i placed 1000uF caps across the output, this has worked well to smooth it out, now the only problem is voltage stays around 34v no load and 26 under load ( some of it is due to sag and some of it is due the caps keeping the voltage high). which is ok except that the motor is rated to 24 volts so i would prefer the volatge was alwasy 26v with or without load.

So im thinking i may use smaller gauge wire and try and put more turns onto it then remove the capacitors on each 36v battery.

[ibza]

Hi
My ebike uses 250watt, 24 volt battery ( Single Plug 8AH SLA Battery controller), but I like to use four 24volt dewalt batteries to get better millage. I understand that your board is prepared for 36volt batteries. I am interested to purchase an interface board for 24volt batteries. Please let me know about the price and the purchasing process. Thank you

[kfong]

The price is listed on the first page, the boards work with both 28volt and 36volt packs. Shipping is $5 or $7 international. Paypal works best for me, but check or money order will work too. Just email me with your order to confirm at kinf@embeddedtronics.com or PM.

Hi
My ebike uses 250watt, 24 volt battery ( Single Plug 8AH SLA Battery controller), but I like to use four 24volt dewalt batteries to get better millage. I understand that your board is prepared for 36volt batteries. I am interested to purchase an interface board for 24volt batteries. Please let me know about the price and the purchasing process. Thank you

[PeteCress]

Just use the NEG FET and POSITIVE output...

Here is my trial balloon for soldering to those terminals:

• Strip the wire so that about 1/2" is showing
• Twist the stripped section
• Tin the stripped section
• Trim the tinned/stripped section to about 1/8"
• Insert said section into the hole
• Apply the tip of a soldering iron to underside of the board (i.e. the side where the non-insulated end of the power wire protrudes)
• Apply solder to the other side of the board
• Withdraw solder and iron as soon as the solder flows

Does this sound like the proper procedure?

I have no clue as to what wattage iron is appropriate.

The irons I have available to me are 15, 30, 45, and 140 watts.

Can anybody suggest which one will do the job but not fry the board?

[kfong]

Hi Pete,

Your list sounds about right. The 45 or the 140 will work, with the higher wattage iron, just remove once you get good solder flow. With lower wattage irons, you need to have the irons in contact with the solder to get it to flow good, it if too low of a wattage it will leave a cold solder joint. This would not be a good connection over time. You can practice your soldering skills on an old discarded electronics boards such as a power supply by unsoldering wires and resoldering them to get a feel for it.

This is the iron to get. 15/150w booster iron
viewtopic.php?f=1&t=15276

Just use the NEG FET and POSITIVE output...

Here is my straw man for soldering to those terminals:

• Strip the wire so that about 1/2" is showing
• Twist the stripped section
• Tin the stripped section
• Trim the tinned/stripped section to about 1/8"
• Insert said section into the hole
• Apply the tip of a soldering iron to underside of the board (i.e. the side where the non-insulated end of the power wire protrudes)
• Apply solder to the other side of the board
• Withdraw solder and iron as soon as the solder flows

Does this sound like the proper procedure?

I have no clue as to what wattage iron is appropriate.

The irons I have available to me are 15, 30, 45, and 140 watts.

Can anybody suggest which one will do the job but not fry the board?

[PeteCress]

...picture of the battery carrier. You can make something similar out of just wood and flat aluminum rails for the support.

Do you have your CNC mill programmed to make those things?

If so, any interest in coming up with a price?

[kfong]

Hi Pete, I can make them but the material is hard to find. Its 1/2" in polycarbonate and rather expensive. Plain Plexiglas is a bit too brittle to last. Aluminum would be an alternative but it takes a while to mill. That’s more time than I wanted to spend. I don't have the X3 mill online, that would make it more feasible. Not sure what other material would work. ABS plastic might be a possibility but I don’t have a good source for it.

[CamLight]

Delrin mills beautifully and even 6/6 Nylon is pretty good for that. http://www.mcmaster.com is where I buy a lot of my raw materials.

[kfong]

I hadn’t thought of nylon that seems like a tough material. I know delrin would be perfect, but that stuff is expensive. Never bought from Mcmaster, seems like a great resource to use. Pete if you really want me to mill out the holders for you. I can charge $20 per holder if you drop ship the material to me. Email me for the address. Each part is .5”x 3.25”x4” Leave about .25” extra in material on each side except for the .5” That will allow me to cut and clamp it. Each part will need to be setup, so there really isn’t any good way for me to automate it. Just choose the material you want to use. If you have to get a larger piece. I can just exchange material for services or mail the extra to you.

I know LI-ghtcycle had success building his own with just hand tools
viewtopic.php?f=3&t=14912

[PeteCress]

Update, looking for a suitable inductor.

When I hook up battery-board-inductor-controller, the CA comes on very briefly then turns off.

After that, when I measure voltage at the inductor-controller connection it's zero. Before hooking it up, it was approx 33v.

If the BMS is tripping, it seems like the board has tb removed from the batt and then re-inserted before it's ready to go again.

Am I right on that?

If so, what are the chances that the ring in my inductor is too small?

Here's mine:

And here's Kin's (from one of the posts above):

Kin's ring appears tb thicker and larger diameter (unless it's rigged with wire smaller than the 14-gauge I'm using... same # of turns, more room left...)

Also, the capacitor is a red herring, right?.... i.e. it just happens to be in Kin's pic and is not used in the circuit.

I know LI-ghtcycle had success building his own with just hand tools
http://endless-sphere.com/forums/viewto ... =3&t=14912

Thanks. I think I will try going LI-ghtcycle's route - especially since right now I can see only needing one or two for my purposes.

[kfong]

Try adding more windings that will increase the inductance. You still have room in the center, wires can overlap. The Toroid is smaller than the one I'm using. I was hoping to reduce the overall size. The red device on the right is a commercial inductor. As you can see the wires on that inductor are just too thin to be of any use. That is why I went with the toroids. Yes, if the BMS shuts down, you need to replug it in. The inductor goes only on the positive side. If you still have problems, I can send you another inductor for the negative side. Not sure why you are getting a shut down so soon, pm me so I can go over your wiring.

[PeteCress]

Try adding more windings that will increase the inductance. You still have room in the center, wires can overlap. The Toroid is smaller...

Wanting to minimize exposure to the PITA factor of soldering Anderson connectors, I bought four welded steel rings, stacked them, and doubled the length of wire.

viz:

Nasty as it looks, it does work - and the bike sure does handle better with just the DeWalt battery in a pannier instead of the 15-lb monster I've been carrying on the back.

Once the Anderson crimping took I ordered arrives, I'll revisit the size/# of windings and see if I can cram enough windings into the smaller purpose-built ring.

Could the fact that I'm running only one battery instead of 2+ aggravate the choke requirement?

In the end, I'll carry at least two batteries, but right now it seems that running only one at a time is going to work for me. When I make the board holder, I will try for an implementation that favors grabbing it with one hand and yanking the battery off and sliding another battery on with the other hand

[kfong]

I hadn't tried just using metal rings. That's a cheap solution. Ferrite is suppose to have better properties but as long as you get results. The original design by Neodymics had a 300uh inductor. Since I don't have an inductance meter. I just wound as much as I could. As long as it works for you. You can have more inductance, just as long as you meet the 300uh minimum. Its sole purpose is to reduce the spikes going back to the batteries, so if the BMS doesn’t shut down then you’re good to go. The only other time it shuts down is when you draw too much current. You will get a pulsating effect. This is different from the spike shutdown.

[PeteCress]

I hadn't tried just using metal rings. That's a cheap solution. Ferrite is suppose to have better properties but as long as you get results. The original design by Neodymics had a 300uh inductor. Since I don't have an inductance meter. I just wound as much as I could. As long as it works for you. You can have more inductance, just as long as you meet the 300uh minimum. Its sole purpose is to reduce the spikes going back to the batteries, so if the BMS doesn’t shut down then you’re good to go. The only other time it shuts down is when you draw too much current. You will get a pulsating effect. This is different from the spike shutdown.

I tried re-winding with 2 and then 3 rings but it wasn't happening.

My final wind is 8' of #14 wire around 4 rings. Put a bead of hot-melt glue between each ring, set the stack on a level surface, hit it with a heat gun to get the rings settled into close contact, and then wound it - dabbing a little more hot-melt on the first and last windings just to keep it easy to handle.

Probably some overkill, but not *that*much.

Seems to be 100% reliable.

Does anybody know if there is any value in how close the rings are? Or is it just the total mass plus the length of the wire?

Once the crimper arrives, I will trim the leads - maybe even solder one end directly into a board.

After a few shallow discharges/charges, I ran one of the batteries flat -riding up and down one of the hills that lead to our house.

Per the CA: 2.165 AH and 65 Watt Hours. That's at 38 degrees F, but with the battery coming from inside the house - so I doubt it had time to get really chilled.

[(79 nominal- 65 actual) / 79] ==> 18% reduction in capacity... which seems to agree with what I've read about temp/capacity

I've got the CA's amp limit set at 12. That pulls 15 amps momentarily but limits it to twelve 99% of the time. That's about 420-440 watts. 400 watts is just fine for what I want to do and I can live with 350... so the rig as it is now seems like a pretty good fit.

Losing 10+ pounds of battery *really* improves the bike's ride/handling.

Tonite I'm leaving the other DeWalt in the garage where it will chill to near-outside temp and we'll see how the capacity holds up.

EDIT:
Next day, I got 61 watt hours: (61/79) ==> 77% nominal capacity. Temps in the mid forties.

[kfong]

http://www.allaboutcircuits.com/vol_1/chpt_15/3.html

Here are some good info on increasing the inductance of a coil. I was trying to find if there is a relationship between thick and thin wire influencing inductance, but so far all I can dig up is the amount of turns and the core material being the most important factors.

One thing worth noting, a looser wrap. Bigger loops creates more inductance. So the limiting factor becomes the amount of wire you can put through the center of a toroid.

[PeteCress]

Maybe I'll take the opportunity to try a loose wrapping on the smaller ring - more-or-less helter-skelter with turns on top of turns.

The small ring works - just needed more turns.

This try was about six feet of #14 wire, twenty turns - which is as many as I could cram into the center of the ring.

It's a good thing that neatness doesn't count.... -)

[PeteCress]

http://www.mcmaster.com is where I buy a lot of my raw materials.

Wow! The Hardware Store From Hell...

That one's a keeper.

Thanks.

[quindiciottobre]

kfong, this is a great job. I'm an electronic designer and I say that this a nice circuit. The price is really honest.

I can't understand why you put that diode. Could you explain me?
But most of all I would like to say that in my opinion will be useful a circuit that drives the DeWalt BMS and its PWM. I think that we could connect directly the motor to the battery and use the internal driver. Don't you think so?

(Sorry for my English)

[kfong]

The diode is needed for battery isolation. It allows you to parallel batteries of different voltages or charge levels. The inductor is needed to prevent the Dewalt BMS from shutting down. On certain motors the inductor will not be needed. I was able to use the boards on a brushed Currie motor without the inductor.

It is possible to use the Dewalt BMS as a motor controller, but you would be limited to using it for brushed motors. Just replace the resistor with a potentiometer. I prefer to use a throttle with a hall effect as the control, but that probably won't interface well with the Dewalt unit. Brushed controllers are cheap to obtain.

[quindiciottobre]

Thank you for your reply.

Yes, you're right. I connected a hall effect throttle with the BMS and in effect I had to put an opamp circuit to extend the 1-4V out of the hall sensor to the 0-5V input of the battery circuit.

I'm building a mini moto for my son. I will post some photo.

[The Mighty Volt]

I like this a lot. How confident are you that the bugs have been ironed out? Thanks and well done.

[kfong]

Not sure what you mean by bugs, I’ve been using the boards on my ebike and scooters for over 2 years now. The only problem you have to worry about is leaving the packs plugged in for over a week, especially if the packs are already discharged. This is because the Dewalt bms requires a small amount of power to work and is enabled once the packs are plugged in. Some of the newer Dewalt packs shut down completely, so it’s not an issue.

I don’t encounter this problem because I take mine out after each ride and just plug it into the Dewalt charger so it’s ready when I take my bike out again. Unlike Nicads, you don’t need to cycle these packs, so I usually have them topped off after each ride. There are already a lot of users on this forum who are using my interface boards.

[PeteCress]

Not sure what you mean by bugs, I’ve been using the boards on my ebike and scooters for over 2 years now....
... There are already a lot of users on this forum who are using my interface boards.

I'm one of the people using them, and have had zero problems. None, nada, zip, zilch, bupkis....

I'm also one of those people who can mess up a wet dream: if something can go wrong in use, I'll make it go wrong.

There's probably a job for me somewhere in product testing....

[Kevinator]

I've been asked to post some more details on how I mounted the interface boards.

Here are pictures of the battery tray I built. I used lexan for the carrier and a lexan spacer between the fiberglass board. The lexan spacer was needed to provide a gap for the screw heads, I would omit it if I could. Wood or aluminum channel could be used. It doesn't have to be as elaborate as my setup. The interface board is epoxied while plugged into a pack so the glue can set while in final position. Once done, the batteries just plug in and lock into position.

Great setup. Those battery trays are really nice! Are you making extras to sell? I'd be interested in a few.

[kfong]

I really wasn’t planning on making them since I would need to source the material. I can charge $20 per holder if you drop ship the material to me. Email me for the address. Each part is .5”x 3.25”x4” Leave about .25” extra in material on each side except for the .5” That will allow me to cut and clamp it. Each part will need to be setup, so there really isn’t any good way for me to automate it. Just choose the material you want to use. If you have to get a larger piece. I can just exchange material for services or mail the extra to you.

I've been asked to post some more details on how I mounted the interface boards.

Here are pictures of the battery tray I built. I used lexan for the carrier and a lexan spacer between the fiberglass board. The lexan spacer was needed to provide a gap for the screw heads, I would omit it if I could. Wood or aluminum channel could be used. It doesn't have to be as elaborate as my setup. The interface board is epoxied while plugged into a pack so the glue can set while in final position. Once done, the batteries just plug in and lock into position.

Great setup. Those battery trays are really nice! Are you making extras to sell? I'd be interested in a few.