I just got 2 18 Volt Dewalt Lith Ion Phosphate
batteries off Ebay.
Looking for advice or pointers on how
to hook them up in series to make a 36 volt pack.
Do i have to worry about the BMS ?
What is the best way to charge them ?
I was just planning on using the Dewalt charger,
so a removeable harness migh make sense.
Thanks for any help and advice for those who have already done this.
If there's a thread on this already, please point me the way.
I saw there was one for the 36 volt Dewalts,
but didnt find one for 18 volts.
Are there differences for these batteries.
I would add that the pack
is for a electric skateboard, and electric scooter.
Both are or will be 36 volts.
For now all I can afford is 2 batts.
But in future I may get more.
The scooter can possibly hold 4 batts total,
the skateboard will only hold 2.
Can I disassemble the Dewalts batts without many problems ?
The part that fits into the tools, is too big and will stick up so it wont fit in the skateboard.
IIRC, they don't have very many Ah at all. Something like 1.1? Or do they use the M1 2.3Ah cells? I don't remember.
Anyway, you might want to give the Makita 18V packs a look. Only $50 for 3Ah.
The author of this post isn't responsible for any injury, disability or dismemberment, death, financial loss, illness, addiction, hereditary disease, or any other undesirable consequence or general misfortune resulting from use of the "information" contai
To my knowledge the 18-volt packs are NiMH not Lithium Ion. Only the 36-volt are Lithium Ion. What is the DeWalt number on the battery pack?
Grandpa Chas S.
These are supposed to be
18 Volt Lithium Ion Phosphate packs,
about 2.4 Ah.
Model DC9180
Here's a link from Dewalts web site
http://www.dewalt.com/us/products/attachment_detail.asp?productID=17730
2.4Ah would mean the same cells as a 36V pack, but only 5 in series instead of 10.
And, WOW is that expensive! That's almost the same as the 36V pack. I'd definitely go for the Makitas for that price. Here's a link for a pack of two and a 22-minute speed charger for $150.
They can't give the same C-rate as the DeWalts, but they handle something like 10C continuous and 12C peak, IIRC, so unless you want to discharge the things in 5 minutes you won't notice any difference. Two of those in series would give you 36V and a possible of 30A. Don't know if the amperage is limited by the battery pack, but since the skateboard is only 10A (fuse is 15A), you should be fine.
The author of this post isn't responsible for any injury, disability or dismemberment, death, financial loss, illness, addiction, hereditary disease, or any other undesirable consequence or general misfortune resulting from use of the "information" contai
It's more like 2.2 Ah
They are not the same cells as the 36 volt packs.
I found this page which has some specs :
http://forum.drc.su/cordless-power-tool-battery-capacity-rating-vt4184.html
Yeah, I didnt pay full price on ebay, so i ended up paying about the same as for the Makitas,
and I got a Dewalt charger too.
I wanted to get 18volt ones, as I can easily make them 36 volt since there are 2,
and the 36 volt Dewalts are too big to fit in the skateboard, and also too expensive.
I also want to have the possiblity to fit the dewalts in the scooter too.
Also I was thinking that the the Li Ion Phosphates were a little safer
than just Li Ion.
Ah, then those are a 5s2p string of their 1.1Ah cells. They use those in the Black and Decker packs, too.
LiFePO4 batteries ARE li-ion. Li-ion encompasses all types of lithium batteries. The Makitas are lithium manganese, which is as safe as LiFePO4; it's lithium polymer and lithium cobalt that are splodie. :)
The author of this post isn't responsible for any injury, disability or dismemberment, death, financial loss, illness, addiction, hereditary disease, or any other undesirable consequence or general misfortune resulting from use of the "information" contai
Here's some pics of my tear apart of the Dewalt packs.
I hope that I can charge them successfully without the BMS.
Not sure if this is a good idea, but I have no choice,
as the batt is too big with the BMS,
and it's a pain to put the BMS back in with the small ribbon cable.
I'll have to find a way to charge these without the Dewalt charger,
as it checks for the BMS.
Without the BMS the connected the connector reads 14 volts,
but before the BMS it reads 19 volts.
I have done 2 test rides on the skateboard.
The added power/torque of the LiFePo4s is great.
My run time was about 15 minutes,
but much more fun than 36 volt SLA.
I used a 1.6 AMP 36 volt charger to charge the LiFePo4's.
It took 1 hour to charge.
I monitored the voltage during the charge.
The charger was finished at about 44 volts, and then cut off.
The 2 18 volts packs in series started out at about 41 volts total.
When the voltage reached 31 volts during the ride, the controller cut off,
to protect the batteries.
I'd rather it didnt have this cut off, as i think the batts could still go to 24 volts total.
I may have to put the 24 volt controller back in, or find a controller with a lower cut off.
For an 18 volt pack, what is the minimum voltage it should be discharge to ?
I would think it can handle down to 12 volts or less.
The minimum voltage you should run the A123 batteries is 3.1-volts per cell. With a 10 cell pack like you are using, 31-volts is correct. Running these cells lower will cause damage and decrease run time.
Grandpa Chas S.
Thanks Chas,
Just to clarify.
I have 2 X 18 volt packs in series to make 36 volts.
The packs are 10 batteries each, for totatl of 20 batteries.
So if 31 volts is cut off that means approx,
15.5 volts per 18 volt pack.
So if I was using the Dewalt 18 volt pack
in a real tool like a drill, it should only go to 15.5 volts ?
Seems like you only really use 2.5 volts of the pack then ?
Your calculations are correct, a 5 cell pack would be @ 3.65-volts per cell (Charged off the charger) and 3.1-volts (Discharged). So the total voltage of an 18-volt pack would be 18.25-volts (Charged off the charger) and 15.5-volts (Discharged). Using voltage to determine the state of charge is not reliable. I use a Cycle Analyst Meter to let me know how many AH I have used during a ride. This is the best way I have found to know what the charge condition of my battery pack is.
The voltage sag on Lithium Ion batteries is small compared to Lead Acid (about half) but still occurs. The voltage sag is the amount of voltage drop the battery exhibits when under load, the 2.5-volts you seem to use from the pack. If you measure the voltage of a 36-volt battery pack at cutoff under load it should not be less then 31-volts or 3.1-volts per cell. However when the load is remove the voltage will return to a level close to 36-volts or 3.6-volts per cell. If you gage the State of Charge (SOC) by voltage you would think the battery is near full charge when in fact it is all but dead.
Lead Acid batteries are effected even more by voltage sag. A 36-volt pack would show 39.9-volts at full charge and 31-volts at cutoff for a voltage sag of 8.9-volts, much larger than the 5.5-volt sag of a 36-volt Lithium Ion pack. This is why the motor slows down on an e-bike using Lead Acid where the same e-bike motor would maintain its speed better using Lithium Ion.
Hope this helps,
Grandpa Chas S.
Yes, it makes sense.
As on the Volt meter it showed the sag and the recovery after load was removed.
Thanks again,