Dewalt Battery Chargers and Battery Balancing

[LI-ghtcycle]

I have noticed something strange, when I charge up my 28v Dewalt batteries, I can put them on the charger a second time, and the surface charge will increase significantly. The average these batteries are showing with a hot off the charger reading is 27.8v but if I take that same battery, and plug it in again for about 20-30 min, I notice that it will increase another volt or 2. The highest charged voltage I have seen so far is 29.3.

I'm not sure if this is anything to be concerned about, but I am thinking that the higher charge has to do with balancing issues (or lack thereof?) I have heard that the Dewalt chargers aren't known for their balancing ability.

I'm also curious if anyone has thoughts on a charger that could be used to charge multiple Dewalt batteries that are still in their original cases to include their built-in BMS, such as in my case with 28v batteries 2s 3p making 52.8 nominal voltage, could a rather simple charger, maybe even an SLA charger that is designed for that voltage be used?

 

[Lyen]

I have noticed something strange, when I charge up my 28v Dewalt batteries, I can put them on the charger a second time, and the surface charge will increase significantly. The average these batteries are showing with a hot off the charger reading is 27.8v but if I take that same battery, and plug it in again for about 20-30 min, I notice that it will increase another volt or 2. The highest charged voltage I have seen so far is 29.3.

I'm not sure if this is anything to be concerned about, but I am thinking that the higher charge has to do with balancing issues (or lack thereof?) I have heard that the Dewalt chargers aren't known for their balancing ability.

I'm also curious if anyone has thoughts on a charger that could be used to charge multiple Dewalt batteries that are still in their original cases to include their built-in BMS, such as in my case with 28v batteries 2s 3p making 52.8 nominal voltage, could a rather simple charger, maybe even an SLA charger that is designed for that voltage be used?

The BMS do discharge the battery over a period of time. Also, it may takes about 20-60 minutes for the charger to balance the cells but not really necessarily if you use your packs often. The voltage will also drop when the packs are cool off after you remove them from the chargers.

Yes, if you tap onto the positive & negative leads on a series of batteries & bypass the BMS you can charge them with a SLA charger. I have done it multiple times at work when I have forgotten I left my Dewalt chargers at home. I also did on purpose sometimes to accelerate the charger time when I was in a hurry. But you have to make sure you do not charge them at more the the internal fuse rating. (15A)

 

[jag]

Having scoured ES archives and read years worth of posts on the DeWalt A123 toolpacks and chargers there doesn't seem to be agreement if the standard charger and BMS is good or not. Basically the two groups of posts are:

1. Several people have used the original packs and chargers for up to a couple of years and thousands of miles without problems or signs of capacity decrease (kfong, cyclomotor engineer etc). So there is some evidence that the DeWalt packs and chargers work well.

2. In some of the first posts goodrum charged packs on the DeWalt charger, then took apart and measured individual cells. He found that cells were out of balance even after allowing for balancing time. Another bad sign is that a lot of the used, defective battery packs offered on the list seem to have a bad BMS and one or two broken cells. So this speaks to that the DeWalt BMS and/or the charger is not perfectly goos/reliable.

Despite reading all the posts I dodn't find any detailed information on the internals or charge cycle of the DeWalt charger. It could be one of:
1. Smart BMS, dumb charger. Basically charger is constant current and BMS (as usually) handles balancing and cutoff.
2. Charger with some charging logic about the charge cycle built in based on voltages. (Like many Lead Acid chargers)
3. Charger with some more fancy signalling (e.g. digital) between it and the BMS.

Options 2 and 3 would make it more difficult to use another charger with the toolpacks and maintain the intended BMS function. Option 2 might allow several toolpacks to be paralleled on one DeWalt charger (for say overnight charging w/o having to swap pack on the charger every hour)

It would be nice if someone could just measure the voltage/current curve of the standard DeWalt charger over a charge cycle. Should not be too hard by just disassembling the charger and put a volt and amp meter on the output.

 

[Lyen]

Having scoured ES archives and read years worth of posts on the DeWalt A123 toolpacks and chargers there doesn't seem to be agreement if the standard charger and BMS is good or not. Basically the two groups of posts are:

1. Several people have used the original packs and chargers for up to a couple of years and thousands of miles without problems or signs of capacity decrease (kfong, cyclomotor engineer etc). So there is some evidence that the DeWalt packs and chargers work well.

2. In some of the first posts goodrum charged packs on the DeWalt charger, then took apart and measured individual cells. He found that cells were out of balance even after allowing for balancing time. Another bad sign is that a lot of the used, defective battery packs offered on the list seem to have a bad BMS and one or two broken cells. So this speaks to that the DeWalt BMS and/or the charger is not perfectly goos/reliable.

Despite reading all the posts I dodn't find any detailed information on the internals or charge cycle of the DeWalt charger. It could be one of:
1. Smart BMS, dumb charger. Basically charger is constant current and BMS (as usually) handles balancing and cutoff.
2. Charger with some charging logic about the charge cycle built in based on voltages. (Like many Lead Acid chargers)
3. Charger with some more fancy signalling (e.g. digital) between it and the BMS.

Options 2 and 3 would make it more difficult to use another charger with the toolpacks and maintain the intended BMS function. Option 2 might allow several toolpacks to be paralleled on one DeWalt charger (for say overnight charging w/o having to swap pack on the charger every hour)

It would be nice if someone could just measure the voltage/current curve of the standard DeWalt charger over a charge cycle. Should not be too hard by just disassembling the charger and put a volt and amp meter on the output.

I totally agreed with you on your comments. Thanks!

 

[bzhwindtalker]

hello

I'm also searching for a way to activate the inbuilt bms when I am charging with a s350 power supply at 29v.
On the dewalt interface board, they seem to have the solution, using 3 resistors between pins of the central connector and the negative side. but I don't know if the maker of the boards will release schematics and all

 

[Lyen]

hello

I'm also searching for a way to activate the inbuilt bms when I am charging with a s350 power supply at 29v.
On the dewalt interface board, they seem to have the solution, using 3 resistors between pins of the central connector and the negative side. but I don't know if the maker of the boards will release schematics and all

The schematic to activate the BMS has already been disclosed 2-3 years ago. You may want to dig deeper on the older posts.

 

[bzhwindtalker]

thanks I will search that.