For the purpose of the thing, I aim at minimizing costs, without sacrificing performance. My idea is to install the pack bare inside the housing, attaching it to the terminals with a truckload of copper wire. My smart & cheap plan is to install the multimeter inside, and attach it to the battery terminals in series with a momentary pushbutton and a small capacitor in parallel with the meter; that way voltage can be easily checked with a small push on it, and the pack is not drained by the voltmeter.
Been somewhat “away” from the forum and related stuff lately, got back to labor nearly a month back now.
This project is “oficially jammed”, I guess the drill's owner really liked the way I restored/upgraded his little laptop's battery pack, he really finds use for it at work.
He may not have liked much the drill pack restoration figures I gave him, but for sure that must have had to do with these facts: a) the drill was a über-cheap piss poor tool, hard for any figures to look good in such a case; b) he may not have real need for it.
Maybe if he finds some extra spare €uros to squander on this stuff soon…
Typical blf mod.
$25 in parts for a $5 drill.
Interesting to see how the rest of it holds up.
Btw a 15a bms will be inadequate.
Stall/near stall may be 50+a!
snakebite, my BMS choices have been influenced on a tad off-topic handful of posts brief discussion I had a few days earlier about restoring a Hilti TE 10A hammer drill power source.
Briefing: 1.2 - 1.4Ah sub-Cs, operating at up to 15A (≈10C cells).
… it more or less becomes clear to me that not even in their wettest dreams would have those AA Ni-CDs provided more than around 8A comfortably. Bottom line: the appliance was a piss-poor electric screwdriver, to start with.
Yesterday I sent inquiries about that inexpensive 15A BMS from Aliexpress to two sellers, asking for the transient/momentaneous operating current values on it. After receiving the same useless copy/pasted answer/information in both cases, already provided in the product ads anyway, I've decided to go with the eBay 15A BMS which, being like the 8A (17A transient current) unit with twice the FETs, I presume its transient current value should also be 2 × 17A = 34A. :THUMBS-UP:
Evaluated ImA4Wheelr's #18 post suggestion regarding those 1-8S li-ion voltage monitors (found 'em on eBay from $1.17), but heck, the stuff is gonna have a proper BMS taking care of independent cell monitoring sooo keep it simple stupid.
you might be surprised at the start surge on that motor.
get your shunt and scope out and have a look.
i would use the bms to charge but not run the motor from it.
it will trip every time you pull the trigger unless that motor is a total wimp.
which is entirely possible knowing what that drill is.
In the eBay ad the BMS board is said to have been tested on a Bosch GSR 7.2 succesfully.
I was also thinking about this but, maybe I could order one of the cheap Aliexpress 15A BMSes and set it in parallel with the one I ordered. Of course, the predicted slight differences in BMS resistances means that the inter-BMS load distribution would differ, but nothing excessive I think. Even if one of them only channels half the current the other does, we would still be at a 22-23A continuous and probably twice that figure for transient current. Shouldn't be very hard to measure load distribution…
My best bet for now, I believe, is to wait for the ordered BMS and take a look at the markings on its MOSFETs. If it ends up needing some current handling improvement, it'd easy to add up to 4 additional ICs stacked upon the ones onboard.
Just checked out eBay, plenty of SOP-8 MOSFET 5-packs for under $1. I wish I were to have a way to know what model does that board uses.
Mmm, been searching for “2S BMS” images on Gmail search but, to my dismay, barely any of them were useful with regards to peeking at their SOP-8 MOSFET IC markings. Most pictures lack detail/resolution and/or their chip markings are “sabotaged”. Could read AO4119 in a couple of unrelated, scant examples.
Mmm, just wanted to save some days by ordering an additional MOSFET pack right now. LoL!
Well, you could save some time, but pay for it in cash, by buying enough MOSFETs to replace the existing ones as well. Then you know you’ve got all good ones on the board.
Mmmkay, not an expert on these matters DavidEF. According to what I've briefly read about MOSFETs, their resistance (RDS(ON) I presume) increases with temperature so they share the load efficiently (current proportionally diverts to the lesser resistance gates).
The important question here is that the circuit is designed to use either N or P-channel MOSFETs, and I don't have a clue about this (literally).
With regards to nice offers there are plenty, a 5-pack of AO4409s for under $1 or a 10-pack for $1.36 sounds great, with just ≈9.5mΩ typical RDS(ON) at VGS = -4.5V and ID = -10A (P-channel MOSFET), so 4-5A of continuous current handling with ease even if cooling sucks. I have nearly a dozen DIP-8 MOSFET datasheets on my document viewer atm LoL.
Already modding before the first outing, where have I seen this before?
Asked the eBay seller what kind of MOSFETs are found on the 8/15A balance BMS boards, though I'd be surprised if the answer is other than “WTF?” or similar.