HPI RS4

Wanted to share with the community and especially for all those interested in buying some Tenergy cells (in my case they are 3500's). Here's is my initial impressions thus far...

I finally got the cells broken down after a slow ~14hr charge @300ma (poor man's equalizing, very slight heat increase will be bled off safely). Now it's off to work I go obtaining as much data as I can about these cells.



The 8 cell hump pack did seem of mediocre quality and I was wondering what those 'red tab stickies' were all about (seen on their site). Well they were just sticky pieces of circular red tape to cover the possibly not so great spot welds. Note that even the wires were not soldered directly onto the cells but rather that shotgun metal material AND THEN that was spot welded onto the battery. Hmmm... never seen it like this before. Anyway that just adds for more resistance which we all know = teh suck.



Ok here's some data for you guys. Reading off the cells in column from left to right. Temperatures taken immediately at the end of the charge through the entire shrink wrapping (to get a relative view). Voltage upon disassembly of shrink. Weight upon removal of spot weld material (as best I can but it would probably be insignificant to get the smallest of pieces left).


Top Left
91.5 F
1.42v
59g

Middle Left
95.0 F
1.417v
57g

Lower Left
94.5 F
1.417v
58g


Middle Top
95.5 F
1.418v
58g

Middle Bottom
95.0 F
1.422v
58g


Upper Right
91.5 F
1.417v
57g

Middle Right
93.5F
1.415v
58g

Lower Right
93.0 F
1.423v
58g


Pack weight before disassembly (deans plug, wires, and all) = 491.29g
Pack peak voltage before disassembly = 11.47v

I got a couple more packs to break down. Now what does all this data mean? Good question! I'm trying to match the cell's voltage, weight, and resistance (poor mans matching). I expected to see a bigger difference in weight to cell voltage (esp. since I've read Tenergy seems to have mah issues) since cells with more mah have more material weight and consequently more voltage. As far as temperatures it is interesting to note and wonder whether the difference in temps is dude to internal resistance of the cell itself and/or that cell being topped off earlier while the others are catching up on charging. What do you think?

And as for those red sticky paper things...



(as seen from left to right: Middle Top - Middle Bottom - Lower right).

Well here's one of the flaws it covered up. Not to say that those suspect cells don't initially show some nominal peak voltage I'd be cautious to use them as it seems their spot welding process (or cycling) has evidently burned both of them (heat damage?) one to even such an extent that it blew the seal (electrolyte crystals?). It has that oily residue on it and a a dark shadow under the Tenergy label (dampness?). I don't think I'll be using those cells in the 'best pack' I'll try to match up.

That's it so far. I will work on the other data later when the others are finishing "warming up". Then I plan to build into side by side packs and try to get a feel for the punch vs run time when the weather allows (forecast says otherwise for a week... I hate rain in the Pacific Northwest!).

*Now my anaylsis is limited to 3500's thus far. YMMV but I didn't expect much since these cells are value based anyway. I will try to get a relative comparison to a different batteries later on (planning to go all side by side), esp with my GP3900's. Now there's something to hope for.

HPI RS4

Alright pack 2 numbers are in!

Same testing procedure as initially mentioned. Note that this time that the temps are down a few degrees since last because the peak charger finished charging (@ 300ma) and kicked down to a 200 ma trickle while I was away. Didn't wanna wait hours to re-peak for the temps to come back up. Still shows relative temperature differences within the pack though.


Upper left
90.5 F
1.423v
58g

Middle Left
93.5 F
1.417v
57g

Bottom Left
92.5 F
1.417v
57g


Top Middle
93.5 F
1.423v
58g

Bottom Middle
94.5 F
1.429v
58g


Top Right
91.0 F
1.425v
58g

Middle Right
92.0 F
1.420v
57g

Bottom Right
91.5F
1.417v
57g

I'm happy to see that upon disassembly of this pack there were no "irregularities" that I happen to came across on pack #1. All cells in this pack appear to be perfectly normal w/o any obvious signs of heat abuse.

I'm still trying to get a feel for what the numbers exactly mean in terms of matching. I'm trying to understand peak voltage vs internal resistance. I've read elsewhere that peak voltage is a good thing "under load" which in my case I cannot measure but rather in an unloaded state. V=IR. If voltage is up therefore the internal Resistance should go up relatively.

My analogy is that more resistance is able to hold up the batteries reading of a higher "voltage potential". Kinda like a bigger dam holding back a bigger river. More potential. However under load that same characteristic (resistance) is detrimental to performance.

Just something I wanted to see if I'm getting right. It would see them my best pack would be one constructed of the lesser voltage? Yet at the same time I thought peak voltage would also be attributed to the mass of materials inside as well i.e. bigger mah cells seem to have more voltage all around.

1 more pack to go coming soon.

Verndog

iTrader: (16)

Why are you messing with the 3500's? The T4500's are way better cells, and still only like $4.50 each. Not exactly too expensive. I run Tenergies in my bashers and really like the T4500 7 cells. I know a couple guys racing with them that claim better power then blue bomb 4200's.

HPI RS4

Because I was looking for some great value to be had in Tenergy (yet to be fully tested) and I saw they had these 8 cell 3500 mah packs for $16. Bought 3 of them to build 4 packs of 6 cell 7.2v.

The math comes out to ~$12 per 6 cell 3000+ mah (being conservative here) pack. Actually less since I had free ship and a little % off deal. So $11 something. Less than $2 a cell!! Not sure where you can find prices like that on any basher pack; even for 3000+ mah packs for less than $12!?

I've also read from other users that the 3500's had way more punch versus the 3800's and 4500's. All being in side by side configuration. This user also quoted that his 3500's had the same if not more punch than his GP3300's. I want to verify this.

convikt

iTrader: (27)

seems odd that your messin' w/ these cells, but I do applaud your efforts
good luck

Verndog

iTrader: (16)

Those are tough to beat prices, best of luck. I have 5 total BL setups up to MM7700 (2) and also have run all the T3500, T3800 and T4500's. No way in heck the 35's or 38's come close to a T4500. You may get near a GP3300 speed on the 35's, but considerably more with the T4500's.

I've hit 49 MPH with just 7 cells in a Stampede 1/10 monster truck with them, and didn't even rebuild the pack.

party_wagon

iTrader: (29)

When you match packs don't match them by voltage & discharge since you will balance them once you discharge them any ways. You want to discharge them all to the same voltage and then measure the time it takes to charge each individual cell. This will allow you turn run the pack, balance it, & then charge it up w/out over charging any of the cells. The reason some of the cells are warm is because some of them charged before the others did.

HPI RS4

Got around to getting pack 3 done. All cells appear good as far as visual quality. I may have to contact the Tenergy rep to see what they can do for me about that 1 (possible 2) defective cells found in pack 1.

*the following data was taken when this pack was left a bit on a longer 200ma trickle charge after re-peaking from 300ma.

Pack 3

Upper left
90.5 F
1.427v
58g

Middle Left
88.5 F
1.416v
58g

Bottom Left
88.5 F
1.423v
58g


Top Middle
90.5 F
1.42v
58g

Bottom Middle
91.0 F
1.429v
58g


Top Right
86.5 F
1.423v
58g

Middle Right
88.0 F
1.42v
58g

Bottom Right
88.5F
1.427v
58g

Now I'm trying to figure out another parameter I can judge by. I have taken current ratings but my voltmeter is limited up to 10 Amps, the readings aren't as steady and teh wires get hot trying to get a midpoint value! It is interesting to note that the heat damage cells reflects this by having a lowering amperage value (as expected more resistance). I will post these amp values later if it makes any more sense.

I have thought of 3 ways to go from here:

Use the V=IR to calculate R and sort by the resistance values.

Obtain 2 voltmeters, one on DC amps and the other on DC volts and hit each cell simultaneously to note the voltage drop under so and so amperage flow.

Direct hook up a cell to a stock motor and note the voltage drop of the cell vs time vs heat build up.

gah... I just wanna get these packs built!

HPI RS4

What are you talking about?!?

First of all I safely overcharged it by C/10 rate to ensure all cells will be throughly peaked before taking values. What I was questioning was the heat from the overcharge. Is the heat from the overcharge an indication of internal resistance? When all cells are topped off for some time now heat is generated from somewhere within, exactly what mechanism and can it be attributed directly to IR? It would make my job easier if this is partly true to spot out the difference in individual cell temperatures in the same pack.

Next for your info... matched packs are composed of cells which resemble as close characteristics to each other primarily in terms of voltage (under load) and discharge capability. Yes mah is a consideration but voltage and internal resistance are of a higher priority. I doubt I have gross mah mismatches when it appears I have cell's weights that are of similar values and they all are all of the same label anyway. I'd think that relatively speaking all cells should a least be within relative to each other in terms of mah regardless of the manufacturer's label.

Your battery's performance is only as good as the weakest link. The cell(s) which have higher internal resistance will just bog down the whole pack defeating the purpose of mixing it in with good/better cells. I'm trying to determine which cells have the least resistance to make packs which will become "good, better, best" types and ID for future use/observations.

Do you even have professional matched cells? Do you bother to pay attention to what it says on the matcher's labels? Please note that people pay a pretty premium for cells that can hold up higher voltages under discharge. This is a sign of low internal resistance. The good stuff. Consequently these will also suffer less heat build up. To you this would be a battery pack that offers serious punch after punch after punch w/o frying itself up.

It looks like from others' advice that it seems the general knowledge is that cells/packs with the least amount of peaked voltage should contain the least amount of internal resistance. That should be the ticket to building the best pack from this lot of cells. I'd rather not try to spend more time obtaining any more cell data (this time under load) unless I really have to.

HPI RS4

Alright... the moment everybody has been waiting for!! (cliff note below)

I sorted my Tenergy 3500 cells by calculating a resistance value based on what voltage and amperage values I obtained with my digital voltmeter. To make it easy I plugged it all into excel and then sorted the 24 cells into 4 groups by resistance: worst (remember this group has the 2 suspect cells), good, better, and best. Since this was my 2nd side by side pack building experience, I decided to build the 'Good' one first for more pack building practice.

For reference I built my packs using Deans plugs (reused the non-gold one that came from Tenergy; still should be good enough), Deans 12 gage wire, Deans racing pro-solder w/ silver, and Deans pro-bar 3.0. All in the name of reducing as much resistance as possible. Remember resistance is the enemy!

For my test I compared the T3500 to a tired ol GP3300 in side by side config and a generic Epic Motorsports 1500 NiCd. I wasn't planning on using the NiCd at the time so I only re-peaked the Tenergy and GP at 2 amps to a temperature of ~125F. I let these cool down to 80's before I ran them.

The batteries were used with an HPI RS4 Rally, Novak Dually Dual, Orion Double Method R 19T w/ s.diode, 12 gage wiring, deans plugs, and an FDR of 5.5 (street setup). Acceleration testing was done on the residential streets.

I first ran the 1500 NiCd. Had the initial punch that we come to know from NiCd's. Though this pack only lasted ~3-4 minutes. At this gearing this is the acceleration and top end that I'm happy with. End temps were 80's for both battery and motor. I also note the Novak Dually Dual never gets hot ever.

Next up was the GP3300 (these are old matched cells from pro-match btw). This one seemed like time and heat abuse has taken it's toll. While the top speed is the same or slightly slower than the previous NiCd run the acceleration was severely lacking; disappointing. Driving with no response from the throttle trigger is down right disheartening. Top speeds on this run lasted for ~7 min before tapering off. Battery: 120F, Motor: 135 F.

Though it was getting dark, I decided to make what little run I could of the Tenergy to get an initial impression after all my battery building work. I let the motor cool down to 90's (though I really wanted to cool it down some more but there's no more daylight; I threw the chassis in the refrigerator for as long as I could wait). I plugged the Tenergy's in and wow... just WOW!! Simply amazing! I know it's obvious what new cells could do for you but this has got to be the biggest bang for the buck (~$15 total cost built). The 3500's had more punch and top speed than the NiCd's, possibly even more than my shotgun GP3900's (another test yet to be run and the GP3900's will be receiving the same side by side treatment as well). Now I can look to even more goodness when I assemble the 'better' and 'best' Tenergy cells of my lot.


In my experience it seems like I discovered my own little piece of gold contrary to the very mixed reviews I've been reading all over the internet... i.e. cheap, poor, decent, you get what you pay for. If your competent to know what your doing and what realistic expectations to set then I wouldn't hesitate to try out some Tenergy cells. I would hope Tenergy would rethink their product line up and offer more side by side configurations to help out their public image but we'll see (common at least do it with your flagship Propel's Tenergy!?). Until then it's all word of mouth (or text so to speak). I seriously think these cells are underrated in the public's opinion and I hope my experience shows people how to extract the true potential of these cells. Since I never was able to run them in shotgun configuration I guess it's what other Tenergy users have said in that it's all in the pack construction, a "night and day difference", I'll attest to that!


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Cliff notes: Tenergy 3500 cells in side by side configuration is a serious bang for your buck deal!!