Making Lipo Packs

[HydroJoe]

I am wondering if anyone here has made any lipo packs. I'm looking to build some 3s1p 2100mAh packs for my T-Rex 450. I have found lots of information on other sites about the topic, but none here. Could anyone direct me to posts here on the subject. Does anyone have any experience in doing it?

I have the soldering skills/equipment to do the job. I have even found all the parts to do it. I'm just looking for some advice from those who may have done it.

[istandalone]

i've never done lipos, but i'm a veteran nicad and nimh pack maker. the most important thing i can stress, is when your working on or soldering the leads and tabs, ALWAYS cover the other one. it's way too easy to short them. and using a metal soldering iron makes shorts easily too. and with lipos, a short might mean a fire. wear safety glasses. masking tape is your friend, using it to cover the tab that your not soldering.

[istandalone]

oh i meant to ask, where are you getting your loose cells? check out www.maxamps.com (http://www.maxamps.com)
pretty good prices there.

[wecoyote]

Most lipo cells have aluminum tabs so I hope your aluminum soldering skills are to par.
I have redone packs and added balance wires to packs that didn't have them.

As was already stated, protect the tabs from shorting aginst each other.

[istandalone]

that's one of the things that's advertised on maxamps, copper tabs.

[HydroJoe]

Yea I like the looks of the MaxAmps cells for the fact they have copper tabs. I have seen nickel plated ones too. MaxAmps cells are kinda expensive though. I think the cells are around $20 each. Doesnt make sense to use them cause I can buy quality packs built for $60. I did find some cheaper ones from http://home.comcast.net/~truerc/prod.htm . At only $13 per cell starts to make more sense.

I don't have any experience soldering aluminum. No doubt I can learn though. Can anyone give me any info on it?

I'm still not sure i'm gonna give it a go....Just doin' a little homework on it.

[HydroJoe]

Most lipo cells have aluminum tabs so I hope your aluminum soldering skills are to par.
I have redone packs and added balance wires to packs that didn't have them.

As was already stated, protect the tabs from shorting aginst each other.

I was just doing some reading on aluminum soldering. Looks like the biggest issue is the build up of aluminum oxide.

Im interested in what you use for:

1. Solder
2. Flux
3. Temps

Most of the info i'm finding is about soldering/welding large pieces of aluminum.

[wecoyote]

For solder and flux I use this solder paste (http://www.allerc.com/product_info.php?cPath=1&products_id=68)
I set my Weller solder station to about 600 to 650 deg F. depending on the wire size I'm attaching to the aluminum tabs. I clean the aluminum with 400 grit emery then solder the two pieces together with the paste.

[istandalone]

just check out that C rating on those truerc cells. 15c and 10c only. depending on flying style/ability, you might draw more then is safe for them. if you're like me, just learning, then they should be fine for hovering and some basic flight.

[HydroJoe]

just check out that C rating on those truerc cells. 15c and 10c only. depending on flying style/ability, you might draw more then is safe for them. if you're like me, just learning, then they should be fine for hovering and some basic flight.

I thought that too but they look like the same specs as these TP cells (2nd on page)
http://centralhobbies.com/electric_flight/tp/tp001.html . I have one of these packs and it works great for aerobatics.(where i'm at.) I can hammer the hell out of it and it's still in perfect condition. Granted, mabey the TP cells are superior quality but for $39 (vs $75-80) it might be worth a go.

The reason I am trying to do this is I really want to get a 500-600 size heli. Thing is, I cant afford the battery cost. I already have spent a fortune on 3s packs (9 of them). I know I could use a couple 3s for a 500 but I would rather not. I figure I could experiment with building packs for my 450 in antisipation for a larger bird.

[HydroJoe]

For solder and flux I use this solder paste (http://www.allerc.com/product_info.php?cPath=1&products_id=68)
I set my Weller solder station to about 600 to 650 deg F. depending on the wire size I'm attaching to the aluminum tabs. I clean the aluminum with 400 grit emery then solder the two pieces together with the paste.


So the technique is the same as standard soldering? Just use the aluminum solder paste? Any special tricks or tips? Do you use silicone insulated discharge wire? I would assume it's copper? Is there any problem soldering copper to aluminum?

[istandalone]

The reason I am trying to do this is I really want to get a 500-600 size heli. Thing is, I cant afford the battery cost. I already have spent a fortune on 3s packs (9 of them). I know I could use a couple 3s for a 500 but I would rather not. I figure I could experiment with building packs for my 450 in antisipation for a larger bird

that's the exact reason i got the hurricane 550. i was thinking trex 500, but it was barely out and i'm kinda waiting for the kinks to get ironed out first. with the hurri and 2x 3300mah packs you'll fly for damn near 8 minutes depending on gearing.

[wecoyote]

So the technique is the same as standard soldering? Just use the aluminum solder paste? Any special tricks or tips? Do you use silicone insulated discharge wire? I would assume it's copper? Is there any problem soldering copper to aluminum?

Works great on copper and copper to aluminum.

[WillJames]

The other thing to remember is that you will need to match the cells for any given pack. If you don't get the matching right, the pack is not going to last. That is the part that is a lot harder than the soldering.

[wecoyote]

The other thing to remember is that you will need to match the cells for any given pack. If you don't get the matching right, the pack is not going to last. That is the part that is a lot harder than the soldering.


And by the time you buy enough cells to find 3 matching you could have bought 2 ready made packs.

[HydroJoe]

The other thing to remember is that you will need to match the cells for any given pack. If you don't get the matching right, the pack is not going to last. That is the part that is a lot harder than the soldering.


By matching cells, I assume you are talking about something other than making sure you have the same type of cells. Could you explain that process to me? If I had to guess I think I would have to do some sort of testing through charging, making sure all cells charge identical? Sounds like a royal pain....not at all cost effective.

[wecoyote]

By matching cells, I assume you are talking about something other than making sure you have the same type of cells. Could you explain that process to me? If I had to guess I think I would have to do some sort of testing through charging, making sure all cells charge identical? Sounds like a royal pain....not at all cost effective.


Exactly.

[WillJames]

By matching cells, I assume you are talking about something other than making sure you have the same type of cells. Could you explain that process to me? If I had to guess I think I would have to do some sort of testing through charging, making sure all cells charge identical? Sounds like a royal pain....not at all cost effective.

The matching process is a trade secret for each company. I think, they capacity and voltage match them for sure, and charge them and let them sit for a time to see where the voltage ends up over time. Not sure what other tests are done, but the matching is what separates the bargain packs from the top brands. It takes time and costs money to match the cells for any given pack. I know the matching is why FP does not repair packs.

The higher amp draw of your application, the quicker an unmatched pack is going to go bad.

[HydroJoe]

Thanks for all the info guys. Looks like I won't be doing this anytime soon. Ohh well....I guess if it was easy (or cost effective) everyone would be doing it. With the reasearch i've done, I think I could at least repair a pack if need be...So not a complete waste of time.