battery medic mod :P fast discharge

Joined
Aug 5, 2008
Messages
116
UPDATE BELOW


oke guys i was messing around when i got the idea to mod the spair battery medics i got to disscharge and balance better and faster so far i moded them cheaply only cost 5$ for the 6.2ohm 4w metal oxide resisters i made it so it can be removed and pluged in if needed its a plug in mod so far i found it takes 30 min to take a 4400ah lipo from 4.2v to 4.0v it gets hot but not to crazy hot its about same temp as the old diy 24ch bms on for forums
best part with thiss mod cases can stay oem except for 2 holes in the sides for the extra wires to attach the the resisters i added to the board
next im going to mod a heat sink to them ^_^ thermal epoxy needs to be found so far found a small tube for 60$ but its only enouf for one board
:(

here is the link to the resisters i got on ebay http://www.ebay.ca/itm/230584620519?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
here are the pics enjoy


the tester ^_^
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the finished product :p

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IMG_0923.jpg
 
oh, this actually works?
I was thinking about doing this with my electrifly cellmatch.. It does make sense but i wonder if there are little FETs or transistors in there that can't handle the added current.. let me know if that mod holds up!
 
well i found the smaller resisters dont get as hot as thay use to only the 6.2 ohm gets hot so it seems like its all bleading off the big 3w resister i added so far so good i did it to a set of semi damaged medics the lcd has dead pixels i whould love for some one to make a lcd mod for them so u can view them on one lcd display and controll them all as one unit now that whould be one hell of a bms is there some on around willing to put the man hours in to figure thiss out ^_^
 
drunkencat129 said:
well i found the smaller resisters dont get as hot as thay use to only the 6.2 ohm gets hot so it seems like its all bleading off the big 3w resister also i check ed the temp b4 the mod and after on all conponents the fets dont get hot the temp is the same as it was b4 the mod so i think this mod works well so far got 3 cycles at out side in a shed during a super hot day and thay havent failed yet i added so far so good i did it to a set of semi damaged medics the lcd has dead pixels i whould love for some one to make a lcd mod for them so u can view them on one lcd display and controll them all as one unit now that whould be one hell of a bms is there some on around willing to put the man hours in to figure thiss out ^_^
 
Just an update the Balancing are still going strong no problems one good thing there good for is lipo chargers that have weak and slow balancing I just use thease Badboys and thay do an amazing job now I'm going to work on a way to include the resisters in the stock caseing just ordered new resisters so I only need. To use one and remove all the small 100ohm resisters and replace them with a resister thats 3.9 ohms 4w metal oxide I'll post picks asap theas moded balencers run nice with meanwell power supply grid chargersetup to charg a 24s3p 100v Turnagy battery pack so far got 20 cycles rock solid charging all cells sit at 4.22v on the nose that charg at 12a at 102vdc I'll post pics with new mod update soon
 
thats good to hear dude.. did you get your medics from HK or ebay? how accurate are yours? some of mine will do plus minus 20mV, not really good for balancing. I now prefer to just use a 12V 60W halogen bulb to manually balance the cells so they get within 5mV just using celllog to check the individual strings. takes about 30 minutes every 500km, not so bad.
 
i ordered both from hobby king and ebay and found thay are acurate the ebay ones are 18$ shiped the hobby king ones are 23$ and thats b4 shipping so far i noticed if the resisters inside the smt ones look smallaller then normal it varrys in voltave 2mv diffrence but thats nothing so far left mine on last night and thay where all at 4.2v all across i checked with my volt meter and thay match up only thing i wish it had was a off option where when thay get to 4.2v it turns them off i ordered a wack load more from ebay there identical to the hobby king ones but theres no sticker lol plus if u get a defective one pay pal covers ur ass in full no dealing with bad customer service from hk lol ^_^ so its worth the risk i think to order the ebay ones now what id love to see is some one make a single display and master board so u dont need to individuly turn them on and set them that whould be amazing
 
UPDATE
here is the finished product its fits in the case and is thin to here are the pics what i did was a removed all the smt resisters on the board and put one 3.9ohm 3w resister that added up to the total value in the end it discharges 1A per cell i did mod it to go as far as 2A but the ballence leads where getting hot lol so i guess 1 is good enouf for me lol also noticed somthing intresting it pulse discharges like for example it puts voltage to the resister then turns off then back on then back off i check on a stock one and it did the same thing

here are the photos
View attachment 2

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IMG_1062.JPG
 
slick, guy!!!

how many times do you think you've used this unit after modifying?
 
Thanks for your hard work. I was gonna buy several of them and link them all up to achieve the same result. :) Saved me a bunch of $$
 
Iv used the first one I did for a year with no problem been useing meanwell supplies to charge 100v 15ah Turnagy packs so far about 19 cycles with the BMs moded thay run good just keep them face down to help with heat next mod is replacing the crappy jst that cause the voltage reading problem with gold pins from pc motherboard or gold plated 32 pin pc printerport conecter or use smaller 9 pin conecters

I wanted to add a heat sink but thermal epoxy costs a lot lol it whould cost 35$ for every 2 BMs boards I'll try some normal epoxy with some arctic silver mixed in see if it works lol
Now all we need is a single screen display to mount on the Handel bars so we can monitor them.
 
Is it still working? :)
 
Still working strong lol lost 3 of my back plates :( so i guess 3 will be be back less lol i got 2 amp discharge out of them max ran them for 20 cycles runs amazing only thing is jst wires get hot lol so ill stick to 1 amp lol disscharge lol also resisters get super hot at 2 amps lol need bigger wattage resisters only useing 3w ones thinking 5 w ones should do the trick or a nice heat sink trying to figure how thay calibrate voltage so i can add a pot and a just them :p i know that use resisters just need to find out where there placed
 
Great to see them going strong dude. Have you ever realized the current rating of those small switchers? It seems they should handle 2A easily on their own, but all the waste heat may give them a hard time without a blower of some kind.
 
Perhaps too low tech but a simple laptop cooling pad running off USB is what I will use to keep the backs cool as I use them and can still watch the screen.
 
acualy i was thinking of mounting the hot side of a pelter to the resisters so it can create power on the pelters positive and negitive side :p saw somthing on instrustables on how to make a power with pelters useing cold or heat :p may be enouf to power a small fan :p if not just slap a bar of copper lol got lots of bus bar from controllers lmao just keep it simple u should see me and stevos junk pile lol R&D at its finest lol
 
I just did this myself but I just saved myself the trouble and simply added the large resistor on top of the others. Sticks out a bit but allows a gap so I can put a blower fan next to it to keep them cool. Doing a discharge test quickly heats them up enough to smell hot resistor. Thanks for the tip! Now I can finally use my BMS charger and have no fear. It's also pretty funny to watch the balance function go crazy when hooked up to a small 2Ah battery.
 
i know what u mean only thing is thay will be few .03 mv off but its not bad id love for them to be dead on but its cheeper then buying a 400$ bms also one tip id do is replace the conecters with good gold plated conecters or u solder some vga conecters to the cells ballence tabs and replace the jst conecter with the vga conecter i did that noticed it reads more acurately
 
I'll look into the VGA connector. I liked your setup where the resistors were outside the medic. I'm looking to build something similar so I can use larger 10W aluminum resistor on a heat sink with a small fan and just leave it plugged in to balance my 20Ah pack. Thanks to your advice it's only taking a few hours instead of several days. :D
 
We are going to do a similar mod on a small batch to see how it works. I am concerned that the additional heat will further degrade accuracy.
Parallel with the stock resistors - maybe just a small boost in balance current. :mrgreen:

So OP has said a few times to replace the connectors... Do you suppose this is because the firmware is reading the cell voltages while driving the shunts causing voltage drops over the relatively high resistance JST-Xh connections? If the voltage measurements are taken when the shunts are off the connector quality should make no difference in accuracy what so ever. You could even put a 100ohm resistor inline since the only current flowing at that moment is whatever the A/D needs for its sample.

They must be measuring the voltage while the shunts are active... that is a shame.

On my BMS I turn off all the shunts for 10mS, measure every channel, then turn the shunts back on. This only lowers the overall balance current by a few percent (99% duty cycle) but increases accuracy by many tens of mV. :wink:

Excited to tinker - waiting on a batch of these.

-methods
 
I would be very interested in buying an 8 cell version of this to use inline with my crappy balancer, damn it takes forever with a 17.4Ah RC Lipo pack.
 
Gotta just hook them up and go to bed.
Keeping them cool will speed up balancing.

-methods
 
.
Hold the phone...

Just talked with my Chinese supplier.... after many emails he expressed to me that the units I was attempting to purchasing were "not good" :shock:
He stated that for $1 more each we can get the units that are "high quality" :p

I have done a lot of business with sketchy Chinese dudes... (including one that took me down a dark alley between two buildings then jumped out and scared me... but that is a story for another time) this guy is definitely not trying to squeeze me for a few bucks. He has clearly stated that there are two flavors of these floating around and he can send me either one. This rings totally true. He is being very fair and forthcoming about ebay fees, paypal fees, shipping fees, etc.

I will keep you guys updated.
I think I might have actually found a good contact for a change

My order has not yet shipped - but once it does it will take only 4-7 days.

I have asked him to clarify the difference between the products - higher precision parts, etc.

-methods
 
Thanks Methods. Interesting in hearing what the verdict is.
 
yea I've just recieved the 'cheaper' version I think... slightly different board layout, different board color too (yellow rather than red). Ill post some pics later if i get a chance, there are a few parts that seem a little different (different part #). the new cheaper one simply has a # ie 3832 vs the red BM witch appears to have a proper part # ie ak992-290 or whatever. Dont know yet what effect it'll have.
 
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