load bank and cut off for discharging?

[isaac_alaska]

i'm trying to discharge my li-po packs a little quicker than the 1.5 hours that it currently takes with my hyperion charger (it only discharges at 50 watts)

i'd like to find about a 1ohm resistor that can handle 500 ish watts. know of any sources? (old tv's, etc.? i can't think of anything right off)

i'd also like to be able to turn the load off automatically when the voltage reaches a desired cut off voltage. i built a small add-on circuit to the bm6 that gives an active high signal of about 4.7 volts when the voltage reaches the cutoff programmed into the bm6 chip. what's the best way to set this up so it will remove the load when it receives an active high signal? i think the current output is only a few mA from the chip, maybe 12 mA

 

[docnjoj]

Check out kfongs smart switch in New Items for Sale. That is one of the reasons I bought it.
otherDoc

 

[dnmun]

you can find the bare ceramic heaters wrapped with nichrome wire, or use the oil radiator type heaters like i do. they will handle the power, and you can add more in parallel to lower the resistance. i have an extension cord with some andersons on the male end so i can plug in up to three heaters in the other end. all in parallel. then just plug the load into the watt meter.

 

[docnjoj]

Also a hot plate or bun warmer is good for about 4 amps @36 volts. More if higher voltage obviously.
otherDoc

 

[heathyoung]

Resistors suck as load banks - a constant current load bank is a much faster (and nicer) way to do this. A number of LM317K's set up in constant current with their output shorted in parallel, all mounted on a whopping great heatsink (or use it to drive multiple pass transistors).

As for your turn-off circuit - I'd use a NC relay with an SCR. KISS principle.

 

[isaac_alaska]

hadn't thought of an SCR but i do happen to have a couple of them sitting around....good idea

 

[auraslip]

here is my discharger/tester

you can output the graphs diretly to a computer or save them on the celllog for later

http://endless-sphere.com/forums/viewtopic.php?f=14&t=30738

 

[isaac_alaska]

nice! time to order a cell log. i'm having trouble getting this bm6 i'm using to output what i want...it's kind of a pain cause it's only made to output 30 mA, and it goes high when the voltage is too low, instead of being programmable to be normally high or normally low. I think i can make it work with a darlington transistor but it's almost 3 am...more soldering tomorrow! really need to get a quick and easy discharger set up...i think these pictures will explain why. i have a problem with acquiring too many liPos..well not too many, just more than i want to manually cycle

still seven short to build the full pack from new batteries, ordering up eleven more though to hopefully cover any bad ones. the other ones with all the ribbon cable on them need to have balance plugs soldered back on them so they can be usable as standard batteries again. SOMEBODY cut them all off last year...and it wasn't me

 

[kfong]

What are all these batteries going into?

 

[dnmun]

UUUUMMMHHHH DONUTS!!!!

do you need to discharge them individually? are you gonna build up the new zephyr BMS richard and gary just finished?

you could use a heater as a load and keep your self warm, or take them camping and use an electric blanket for winter camping in the snow. whatta lotta power piled up there.

UUUMMMHHH DONUTS!!!!!!!!!!!!!!!!!!!

 

[isaac_alaska]

all of the new ones are going into an electric snowmobile project we're working on. anyone close to alaska and want to help out?

not sure what we're going to use the old ones for yet, but so far we've been using them in the electric trike i built. kmx tornado frame, and used a hacker A200-8 motor in it. Powered by a castle creations ICE HV 160, it will pop 100 amp fuses almost instantly if you hit the throttle hard. 200 amp fuse though and it works wonderfully. we usually run four of these packs, for 48 volts at 10 AH. the motor is good for 16kW though so you can do some SERIOUS tire burning action if you want to. definitely a recommended motor if you really need high power

 

[kfong]

Isaac, I just built a 500 watt load that was easy to make.
http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=33218

 

[ZOMGVTEK]

In a few days I will have the spacers for my 2kW resistor bank. 10x 200W 1 Ohm wirewound resistors screwed to a board. I could throw a fan on it for extended high power testing, but they take 100W no problem. Sure do get toasty when dissipating 200W, but they are supposedly rated for it.

I have yet to find a cheaper and more capable way to throw power away. This setup can go from 10 Ohms at 2000W capability, down to 1/10th ohm. Should be good for most anything I work with, 12-150V. It sure is massively inductive, but thats not a big deal for most applications.

 

[isaac_alaska]

where did you find your resistors? the ones i was finding were pretty expensive in that size...it seems like they were about 20 dollars each. i might be mistaken though..

*goes to check ebay*

 

[ZOMGVTEK]

I managed to get 10 of them for $50, shipped. They're even adjustable.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=220570221323&ssPageName=ADME:X:RTQ:US:1123#ht_500wt_1413

Of course I'm totally unwilling to pay full price, so we did a shady off-eBay transaction.

Heres a video of them in action, the last 2 ohm test was 5kW into two of them. They melted the carpet a little, but managed it.

http://www.youtube.com/watch?v=ygPYZWgnjO0

 

[isaac_alaska]

that's certainly the way to go...i found a really good deal on 1 ohm 10W resistors (60 of them for five bucks) but they're over in the uk, 17 dollars shipping, and won't get here for a month. sad days. i didn't buy them

 

[ZOMGVTEK]

You generally need to dig into some obscure search terms before you find the good stuff.

Definitely look for the big ceramic style ones that are designed for free air operation. They are super easy to manage, and are easily available in 1 Ohm 100W / 200W variety. Hook power up to them, they get hot. Magic.

If you're lucky, you can find some non-inductive winds. Not a big deal for just discharging a battery, but it gets nasty above a few kW.

 

[auraslip]

I saw pics of some guy soaking big resistors in buckets of ice water. Should be easy for ya. just go get some of that white stuff that falls from the sky up there

or use a bunch of bulbs to heat your lab.

 

[isaac_alaska]

so i found these....and they seemed like a good deal so i figured i'd try them. i ordered ten of them. 1.2kw, and they SHOULD be super easy to connect up....just stick some big ol' connectors on the ends of them

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=400243358654#ht_2164wt_1270

 

[isaac_alaska]

they wont' ship them to me....even though their ebay page says they will. so i connected five packs in series to give me close to 120 volts, and now i'm discharging them through a big 1500 watt radiator type heater. takes about 17 minutes to discharge them

if my second charger was working i could really start putting some cycles on these packs. i'm still initially charging, balancing, discharging, charge-to-70% on my hyperion charger, but each pack only gets that treatment once. then it goes into a pack of 5 in series to get charged and discharged in bulk

 

[izeman]

i'm gonna use 2x 50w resistors screwed to a cpu cooler with fan. they are capable of removing heat of 100w easily.
i'll post pictures when done. but to be honest i do this because i like modding things using 2 or 4 12v 50w halogen bulbs in series and or parallel does the job much easier ...

 

[isaac_alaska]

I'll post pictures if my radiant heater discharger when I get back on Monday. I added a dc breaker inline with the power cord to it so I can disconnect power and then unplug it. Otherwise it was arcing pretty bad and making my bullet connectors look really smoked. I'm able to dump 1500 watts of heat without any cooling fans. If I want to go bigger, I'm thinking of getting a shunt wound dc motor, coupling it to an ac single-phase generator, and pumping the energy back into the wall instead of wasting it as heat. We learned how to synchronize a 3 phase generator to an infinite bus in one of my power classes (and actually performed all the steps hands on) so a single Phase setup would be super easy

 

[ZOMGVTEK]

The spacers showed up a bit early...

Now I just need to make a bunch of jumpers to easily configure them in series/parallel.

 

[isaac_alaska]

You could attach tubing nipples to each end of each resistor and pump water through them. The pumps for doing liquid cooling in computer cases would be about perfectly sized

 

[isaac_alaska]

got a 1500 watt discharger with automatic cut-off working now...here's some pics. it's not as pretty as some of the ones out there, but it works well

that ammeter says i'm pulling about 11 amps, and i'm pretty much right at 120 volts. i used 5 bm6 chips (because they're really cheap compared to most of the other bms things i've seen, such as a cell log) and built a circuit that lets them cut off the big contactor as soon as any of them beep even once. that huge scr is the only one i had available, it's a little oversized for the job since it's only carrying about 100mA (and rated for upwards of 1kA)
i used an additional relay so i could make the main contactor stay closed until it receives an active high signal.
the 12V battery is for running my relays (and buzzer when the pack is done cooking.) probably could have used a computer power supply (or any other 120-12V dc-dc) but the battery was quick and easy, and doesn't put any extra drain on the pack after the relay goes off.