Building A Ludicrous 14s2p SPIM08hp battery

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thorlancaster328   10 W

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Building A Ludicrous 14s2p SPIM08hp battery

Post by thorlancaster328 » Mar 01 2020 2:11am

About a week ago, I stumbled upon a really amazing deal for the SPIM08HP lipo batteries a lot of high-power bike builders have been talking about for the past few years. The seller (batteryclearinghouse) was offering 32 cells for a bit over 75 dollars, and it was simply too good a deal to pass up.

The batteries were packaged poorly and some were puffy and/or bent, but they included extra batteries. Of the 39 batteries sent, 33 of them were good enough to move on to the next stage.
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According to several posters on this forum and elsewhere, these cells need a bit of cycling to restore full performance after sitting in storage for a few years. I divided the cells into 3 groups of 11 based on the voltage they arrived at. Right now, they are only soldered together with small-gauge wire. This is good enough for charging at 14 amps. When the final pack is built the tabs will be soldered directly together for near-zero contact resistance.
Charging.jpg
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To discharge the cells between charges, I am using a 2-ohm subwoofer and hooking up one to two packs in series. Once I get 3 packs made, I will be able to hook this to my bike's MPPT charge port and get the initial few cycles completed much faster, as well as not outright wasting electricity heating up a big voice coil.
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After cycling, I will arrange the good cells by capacity and IR to maximize the strength of the weakest group. If needed I might make one of the parallel groups out of 3 weaker cells. Initial testing of one cell yielded a bit over 8 amp-hours and 4 milliohms, but I have no idea of how the other 32 selected cells will perform.

The end goal for this project is to build a 16 amp hour, 14s (52 volt nominal) battery that can comfortably do 200 amps continuous, even after battery derating due to age. My bike maxes out at 100 amps of peak battery current, and could likely do 120 amps if I upgraded the rear motor phase wires (which I am planning to do this spring break). This battery would be more at home in a more powerful build, but it should be able to push my bike (viewtopic.php?f=6&t=99445) up to a peak speed of around 55-57 MPH on flat ground.
Find weakest component, upgrade it, repeat until satisfied. Rome was not built in a day.
When in doubt, get bigger MOSFETs / Batteries / Motors / Etc.

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Re: Building A Ludicrous 14s2p SPIM08hp battery

Post by larsb » Mar 01 2020 4:40am

I doubt you’ll find any large improvements in upgrading phase wires, it’s a common myth for most motors.

100–>120A is 44% higher ri2 losses and what sets the limit for the motor is mostly internal heat in the motor, not in phases or connectors. For sure you can melt for example an old anderson pp 45A connector outside of the motor but i’ve needed them to be old and over 200A phase current to get issues.
Ride on!

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Re: Building A Ludicrous 14s2p SPIM08hp battery

Post by thorlancaster328 » Mar 03 2020 9:41pm

My rear motor's peak power / torque is only limited by how much current I can send in. If I send more than about 45 battery amps during hard acceleration, the wires going from the controller to the rear motor get too hot to touch. The fact that I rewound my motors motor for higher KV is also contributing to the issue.
Adding thicker phase wires is not going to increase my continuous power, but it will increase the amount of safe peak power. I have an 18-FET controller for my rear motor. Currently the phase wires are the bottleneck when it comes to acceleration. Upgrading them from 16AWG to 12AWG should enable me to run around 70 peak battery amps instead of 45-50.
Find weakest component, upgrade it, repeat until satisfied. Rome was not built in a day.
When in doubt, get bigger MOSFETs / Batteries / Motors / Etc.

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Re: Building A Ludicrous 14s2p SPIM08hp battery

Post by memy » Mar 04 2020 8:05pm

Adding to the SPIM08HP picture.
I received 40 cells from batteryhookup a couple of days ago (12AUD shipped), well packed and no puff's and nothing bent.
First cell managed nearly 7ah discharge (4.2 to 3V at one amp) and 7.3ah to get the juce back in. (3amp charge).
Second cell looks the same.

Was planing on running 20S 1P for short hop to the train station. (45amp greentime ,HBS36 golden motor)
(Currently using 4y old 18X 5amp Turnigy (73V) but don't like the $$ sitting at the station)

Looking at how these cells SAG under a 1amp load I'm suspecting they are going to disappoint compared to my worn (well looked after Turnigy bricks).
A few pictures below
Look foward to seeing how your tests go.
IMG_20200304_190507_c.jpg
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(One Amp load voltage goes to 4V in the first 5mah of discharge).
IMG_20200305_072347.jpg
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Really! 3.62V at 1amp discharge after only 2.5amp hours used. (Current cell under test)
At a glance IR looks crap to me, not sure if it is even worth using these.


I'm regretting this pile now
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Re: Building A Ludicrous 14s2p SPIM08hp battery

Post by flat tire » Mar 04 2020 8:36pm

Those cells especially old probably aren't gonna be happy doing 12+C continuous let alone peak. Fortunately you won't be using anywhere near 200 amps continuous even at 14s on a bicycle doing under 60 mph unless you are on a track racing. If you're racing you want lithium cobalt which is available in much higher discharge and only keeps fresh a couple years.

This looks like a "you get what you pay for" situation.

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Re: Building A Ludicrous 14s2p SPIM08hp battery

Post by docrocket » Mar 04 2020 11:18pm

You might be jumping the gun. I recall reading another builder writing about these cells and how they stuck at 3.6v for a loooong time under load, i.e., that's where most of their juice is. They might not be high-performance but in adequate numbers I gather that they keep the voltage up and have amp-hours for days.

Or you might be totally right and we're boned. I ordered 40 too, and they got here today. Have one on the charger now for a discharge/charge cycle. I'm intending a 48v 13S3P

Question for you: I do not have balance leads. Can I still string 6 of these together on the charger (same model you have) for a discharge cycle if they have close starting voltages? I know I can't CHARGE them together until I have their known voltage high end and can match cells, but can I accelerate the discharging side of things? Thanks.

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Re: Building A Ludicrous 14s2p SPIM08hp battery

Post by memy » Mar 07 2020 8:22pm

The imax is like any lipo hobby charger, it won't do anything without the balance lead.
Yeah they stick at 3.6V for quite some time, hope to test a few today at 10 amps and see what the watt hours look like.

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Re: Building A Ludicrous 14s2p SPIM08hp battery

Post by spinningmagnets » Mar 07 2020 8:36pm

Maybe ten years ago, the 9-Continents hubmotor was the common option. The first step was to use high volts, and then to increase the size of the phase leads to see how many amps the stator could take. The axle was hollow (unlike the hubs today), so after a deburring and reaming to smooth-out the tunnel irregularities, the fattest copper bundles that would fit were squeezed through the hollow axle. The amps were raised until the internal temp gauge showed it was at the max advisable (based on the temps of previously fried stators).

I mention all that so I could say this...

Just for laughs, they then doubled the phase-wire thickness of cross-section as soon as the cable exited the axle. Under the same loads as before, the stator ran cooler, and could then take more amps. It was speculated that the external copper wire acted as a heat sink, and being open to the air, it was able to shed "some" of that heat.

Nowadays, I'm sure that using ferro-fluid would be a much better and more effective option, but...why not do both? I have clipped a few cords from vacuum cleaners on trash-day, so I have tons of free high-strand count flexible wire. Free wire is cheap, why not use it?

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Re: Building A Ludicrous 14s2p SPIM08hp battery

Post by docrocket » Mar 07 2020 9:11pm

The amps were raised until the internal temp gauge showed it was at the max advisable (based on the temps of previously fried stators).
Ah, similar to the way we test bridge maximum loads today - drive heavier and heavier trucks across it until it collapses. Then rebuild the bridge and put up a sign saying the max load is a little bit less than that truck's weight.

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Re: Building A Ludicrous 14s2p SPIM08hp battery

Post by docrocket » Mar 07 2020 9:21pm

memy wrote:
Mar 07 2020 8:22pm
The imax is like any lipo hobby charger, it won't do anything without the balance lead.
Yeah they stick at 3.6V for quite some time, hope to test a few today at 10 amps and see what the watt hours look like.
FYI you can turn balance charging off for LiIo.

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Re: Building A Ludicrous 14s2p SPIM08hp battery

Post by memy » Mar 07 2020 10:43pm

Hi Ron,
Yeap all done bar the hub sinks.
IMG_20200308_130700c.jpg
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Can't remember if the gm is a 28mm or 35mm sator but it still suits me travel wise at 60V. 20Ah18650PF
Beyond 18cells I keep the controller speed switch at one else it just runs on the current limit the whole time. Torque at 22 cells is just not there just lots of heat.

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Re: Building A Ludicrous 14s2p SPIM08hp battery

Post by thorlancaster328 » Mar 10 2020 2:45am

I've been pretty busy with college for the past couple days and have finally finished categorizing my battery pack. I will be using 32 cells to make a (mostly) 2S14P pack, with 3 cells on 4 of the parallel groups because they have weaker cells. According to my measurements and calculations, the finished pack should have around 33 mΩ of resistance at 4.1v/20°c. When the battery warms up and isn't fully charged (IR goes down near mid-SOC and higher temperatures during summer riding) I'm expecting the IR to drop into the low 20s of milliohms.

For under $80, a pack that holds 750 watt hours and can put out 180 amps is a total steal even if it only lasts a single season. Given that my bike peaks at 130 and can only do 70 continuous amps, I should get 2 or 3 years out of this pack. Now I'm wishing that I had a beefed-up motor like SpinningMagnets (or LiveForPhysics :lol: my battery would probably :flame: if I tried to do that much power).

Spreadsheet of cell data: https://docs.google.com/spreadsheets/d/ ... sp=sharing

Docrocket, You're correct about jumping the gun on the voltage cut-off. When I capacity-mapped a random cell (viewtopic.php?f=14&t=54202&start=75), it showed that most of the charge was stored between 3.6-3.8 volts resting. Under a moderate load, you'd lose a TON of capacity if you cut off at 3.6. Personally I'd set the LVC for when the weakest cell hit 3.1v under load. These batteries are rated for discharge to 2.5, so 3.1 won't hurt them a bit.
Regarding your question about balancing, NO, it's not a good idea to not balance, especially if the cells aren't matched to begin with. If you had a pack with 5 strong cells and one weak cell, the weak cell would be way overcharged by the time the strong cell hit 4.1 volts. If you don't have a balance charger or lead, charge only to 4.0 volts/cell and then balance by hand (or put them all in parallel like I did).
Find weakest component, upgrade it, repeat until satisfied. Rome was not built in a day.
When in doubt, get bigger MOSFETs / Batteries / Motors / Etc.

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Re: Building A Ludicrous 14s2p SPIM08hp battery

Post by docrocket » Mar 10 2020 4:44am

I'm in the experimenting-and-making-lots-of-sparks portion of the process personally. I've aborted two builds thus far; I'm just noodling around TBH. I've never built a battery before.

These things are kind of a pain in the ass to work with, I'll say that. Four g-d surfaces to guard against short circuits. The Electricity Fairy thinks I'm trying to make a pass at her or something.

How are you doing the 4P configuration? Heavy busbars? I've been playing around with just using nickel nuts, bolts, and washers to bind the individual packs.With that setup, 3P is pushing it. (If you wanted to do a MASSIVE parallel pack, you could put them in a spokes-of-the-wheel configuration.)

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Re: Building A Ludicrous 14s2p SPIM08hp battery

Post by DogDipstick » Mar 10 2020 8:49am

thorlancaster328 wrote:
Mar 10 2020 2:45am
According to my measurements and calculations, the finished pack should have around 33 mΩ of resistance at 4.1v/20°c. When the battery warms up and isn't fully charged (IR goes down near mid-SOC and higher temperatures during summer riding) I'm expecting the IR to drop into the low 20s of milliohms.

No I would bet it would be much more...... My 20s pack of 1mOh cells is not 20mOh, what makes you think this one will be? Most ir I measured on these is in the 6-8mOh..... each.. It will be significantly higher and the sag will be also. Fr instance, the lowest I have ever seen my pack displayed at is about .030 Ohm. I have seen under 30mOh, but only on tiny discharges, not real life scenario.. and I dont know how CA3 accurately figures this number.. exactly.. ... but it does. I really doubt the low 20s.. gona be more like in the 60mOh or 80mOh range ... Or higher.

For under $80, a pack that holds 750 watt hours and can put out 180 amps

Mine cost 160$ and 1270 wh( recycled ev cells) and can put out 2000A+.. and 270A contin on the same calculator....Some two years already....



I honestly doubt any longevity with a 180A discharge..

they are 125A max cells, empirically, based on 7.2Ah and IR of 6mOh... and not going over 6w/heat/Ah capacity....


How do you count your mAh again? Can you see if you put more inthan you take out oon a cycle?

When I capacity-mapped a random cell (viewtopic.php?f=14&t=54202&start=75), it showed that most of the charge was stored between 3.6-3.8 volts resting.

I got a different capacity map, but somewhat similar. I did use a high end fancy PID loop controlled SOC map generation. Mine takes two discharges into account at different PIC dontrolled C-rates....


Regarding your question about balancing, NO, it's not a good idea to not balance, especially if the cells aren't matched to begin with. If you had a pack with 5 strong cells and one weak cell, the weak cell would be way overcharged by the time the strong cell hit 4.1 volts. If you don't have a balance charger or lead, charge only to 4.0 volts/cell and then balance by hand (or put them all in parallel like I did).

Machine balancing is the best. Yes I would absolutely NOT bulk charge these too much, the IR varies to much, the capacity varies too much, and the cells even have transient voltages leaking into the pouches sometimes, well known and seen in the DIY community. I bulk charge my lipos and they are 10X more behaved than these. I hit em with 100A and drain em often.. It will be interesting to see how long they last with a good long data set ( lifespan) and to see how hard the BMS works... Keep us posted.
Allota Watts @ 83.1v of raw QS power takes me everywhere on my Ironhorse DW link XC... :) Powered by Chevy. :D Broke 10 horses the other day. ( BTW; ...don't get hurt... :? )... (Currently building a battery datalogger.). :roll: Playin with (24) IRFB4115s now. :wink:

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Re: Building A Ludicrous 14s2p SPIM08hp battery

Post by thorlancaster328 » Mar 10 2020 11:19am

In terms of internal resistance, you're getting such a big number because you're not paralleling the cells in your calculation. Sure, if I made a 14s1p pack from 14 random cells I'd probably get around 60-80 mΩ, but my pack is going to have 2 or sometimes even 3 cells per parallel group (for the weaker ones). It should be 30 mΩ easy, likely less, testing will tell if this is the case.

As for cost, I got these from batteryclearinghouse on eBay, not batteryhookup. There were a few duds but manual testing weeded them out and they are not in the spreadsheet.

Regarding capacity, My ISDT Q6 says they hold that much, and it's never given me any trouble before, so I don't doubt its accuracy. Other people have also reported between 8000 and 9000 mah from these packs, so I'm trusting my charger here.

Also where did you get those recycled EV batteries? I'd love to have a pack with that kind of performance per dollar.
Find weakest component, upgrade it, repeat until satisfied. Rome was not built in a day.
When in doubt, get bigger MOSFETs / Batteries / Motors / Etc.

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Re: Building A Ludicrous 14s2p SPIM08hp battery

Post by spinningmagnets » Mar 10 2020 11:25am

This type of cell will perform better, last longer, and "puff" less if you add compression plates to the flat faces. Just add one to each end of the stack.

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Re: Building A Ludicrous 14s2p SPIM08hp battery

Post by DogDipstick » Mar 10 2020 11:38am

thorlancaster328 wrote:
Mar 10 2020 11:19am
In terms of internal resistance, you're getting such a big number because you're not paralleling the cells in your calculation. Sure, if I made a 14s1p pack from 14 random cells I'd probably get around 60-80 mΩ, but my pack is going to have 2 or sometimes even 3 cells per parallel group (for the weaker ones). It should be 30 mΩ easy, likely less, testing will tell if this is the case.

As for cost, I got these from batteryclearinghouse on eBay, not batteryhookup. There were a few duds but manual testing weeded them out and they are not in the spreadsheet.

Regarding capacity, My ISDT Q6 says they hold that much, and it's never given me any trouble before, so I don't doubt its accuracy. Other people have also reported between 8000 and 9000 mah from these packs, so I'm trusting my charger here.

Also where did you get those recycled EV batteries? I'd love to have a pack with that kind of performance per dollar.
No. I xconsidered the fact that you will be paralleling.

I often wonder if "Battery clearing house" is an offshoot of " Battery Hookup"... They always seem to have similar offerings and whatnot... IDK though.

I thought you were manually calculating the Ah.. Good that you have an ISDT. That makes all the diff. Accuracy.

I find the cells ( in general any cell) that takes more Ah IN, than OUT on similar rates datalogged over cycles... is a battery cell going south. Wasted charge efficiency, in heat, on charge. Showing as though the charger is putting more in than taking out,on repeated cycles. I saw that alot ( empirically) in my testing of these (SPIM08) cells ( and other lesser quality no name lipo). Other cells dont show this.

I got my cells from Art @ Greentec. I have bought alot from him and he has treated me well and honestly. I use 3 (6s) and one (2s) in my build so I can break down and datalog them after a time and again. Problem wiht my Chevy Volt cells is the bulk.. the SPIM08 are really a much better PHYSICAL size to build ebikes with.. and stuff full o capacity. Yeah, EV cells are absolutly the way to go in the future, and before I build with 18650 Im definitely buying these for a go at that price (<75$Kwh? yeah).


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Allota Watts @ 83.1v of raw QS power takes me everywhere on my Ironhorse DW link XC... :) Powered by Chevy. :D Broke 10 horses the other day. ( BTW; ...don't get hurt... :? )... (Currently building a battery datalogger.). :roll: Playin with (24) IRFB4115s now. :wink:

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Re: Building A Ludicrous 14s2p SPIM08hp battery

Post by thorlancaster328 » Mar 10 2020 12:21pm

Those GreenTec auto cells look like a great deal. At only 5" by 7" (out of the pack) they are a bit chunky but they should fit in my center triangle.

I've charged my cells at 10 amps continuous and could not feel them getting noticeably warmer than the ones sitting on the bench. I haven't done any tests on colombetric efficiency of them, but I suspect you got a bad batch of cells.

How did you get the figure of 60 to 80 milliohms? Even with each cell at 6.25 milliohms (the worst I measured), the pack would only be 44 milliohms. Interconnect resistance should be only 2-3 milliohms, tabs will be soldered together like a standard lipo and I will use three 14AWG wires running in parallel to the XT90 discharge connector.
Find weakest component, upgrade it, repeat until satisfied. Rome was not built in a day.
When in doubt, get bigger MOSFETs / Batteries / Motors / Etc.

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Re: Building A Ludicrous 14s2p SPIM08hp battery

Post by thorlancaster328 » Mar 10 2020 12:29pm

SpinningMagnets, I was considering adding compression plates on both ends and after a bit of research it sounds like a good idea. I plan on using some 1/4" high density fibreboard and fiberglass-reinforced strapping tape to apply pressure to the cells. To evenly distribute pressure across the face of the cells, I will glue another sheet of fibreboard to the center of each end-piece.
Find weakest component, upgrade it, repeat until satisfied. Rome was not built in a day.
When in doubt, get bigger MOSFETs / Batteries / Motors / Etc.

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Re: Building A Ludicrous 14s2p SPIM08hp battery

Post by DogDipstick » Mar 11 2020 9:26am

thorlancaster328 wrote:
Mar 10 2020 12:21pm

I've charged my cells at 10 amps continuous and
colombetric efficiency of them,


but I suspect you got a bad batch of cells. ( I have tested many many different cells... and see it in everything from 18650 to 60Ah lipos.. and many other cells. In facT ai hve in possesion some Lipo that if the same shape and 35Ah / cell as the Volt ones that I am building with this moment...0.9 mOh IR) What I am saying it was not one "batch" that showed this... It is inherent to many different lithium chemistry. Easy to see if your charger puts more in than it takes out. Good cells do not tdo that.) ( the ones that die short lives do)

How did you get the figure of 60 to 80 milliohms? Even with each cell at 6.25 milliohms. (the worst I measured), the pack would only be 44 milliohms (bet it will be more). Interconnect resistance should be only 2-3 milliohms ( not even), tabs will....

I use an microprocessor to gather the data and empirically put it on a display. From my experiences, with the many cells I have run, the many packs, and the experiences I have had in doing so.... Thes SPIM cell is wimp and old ( compared to many I have tested) and the more you stack, the more the pack IR wanders from the " calculated by 'human with math and data points" theoretical" to the " empirically, microprocessor measured and displayed... "

Your charger is reading a little low Id say. I use a hobbyist accepted standard, the powerlab. Got 8mOh over and over again. Or more? I think... Quality and accuracy of the ADC, a little better than the ISDT IMO.

In theory 44mOh.. BUT.... , but based on empirical data I bet it wouldn't be that low. Temp make sa big difference with these cells too.

Basing my experience on many miles, datalogs, and seeing the well known and accepted CA3 algorithm ( dcir) of the pack in real world use everyday scenario.... shows me the V drop and the subsequent IR. .. in realation to power out and temp. ... and what I learned looking at these things...

If you have an accurate way of ACIR the whole pack cell for cell, whole pack totaled... ... I would love to see the empirical data... but until then, ....

You have a CA3? That will show you a good reading.
I am sure it wil be powerful, ( more than 18650) but not as powerful as real ~1mOh cells.... and with my 20s pack the CA has shown a min of 32mOh.. Thereabouts. .. And they are ~1mOh cells.... and if your pack is 40 cells of 6-8mOh ea .. well you see the math.
Allota Watts @ 83.1v of raw QS power takes me everywhere on my Ironhorse DW link XC... :) Powered by Chevy. :D Broke 10 horses the other day. ( BTW; ...don't get hurt... :? )... (Currently building a battery datalogger.). :roll: Playin with (24) IRFB4115s now. :wink:

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Re: Building A Ludicrous 14s2p SPIM08hp battery

Post by thorlancaster328 » Mar 11 2020 10:00pm

I don't have a CAv3, I have a homemade Teensy 3.6-based system that can measure volts and amps, calibrated against my multimeter. Once I have time (next week is Spring break), I'll write a program that sets the current to a low value (~10A) for 10 seconds, measures the voltage, sets the current to a high value (~30A) for 10 seconds, and then measures again. IR results (dV / dI) and voltage vs mAH used will be logged after each 20-second interval into an external 4k EEPROM that I will read out and graph.

If I had a CAv3 I could compare my pack IR with other users', but I think my method will be pretty accurate given how DC IR is typically measured at 10 second intervals. Given how the tabs will be soldered directly together like a standard hobby lipo, my interconnect resistance should be minimal.

We'll see what the results are in a few weeks. Even if they aren't great, my motors overheating will still be the limiting factor by far.
Find weakest component, upgrade it, repeat until satisfied. Rome was not built in a day.
When in doubt, get bigger MOSFETs / Batteries / Motors / Etc.

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Re: Building A Ludicrous 14s2p SPIM08hp battery

Post by DogDipstick » Mar 11 2020 10:51pm

Cool. I will love to see your results.
Allota Watts @ 83.1v of raw QS power takes me everywhere on my Ironhorse DW link XC... :) Powered by Chevy. :D Broke 10 horses the other day. ( BTW; ...don't get hurt... :? )... (Currently building a battery datalogger.). :roll: Playin with (24) IRFB4115s now. :wink:

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Re: Building A Ludicrous 14s2p SPIM08hp battery

Post by memy » Mar 12 2020 3:51am

In comparison my method is as rough as guts.
Tested 3 random cells with a boost converter load. They happly supplied 18amps for some time, before the boost converter started to have issues as the voltage went below 11 Volts. Stopped the discharge at 6AH (3.43V per cell very closely matched.
Total of 65.42wh
After seeing the sag with a one amp discharge load, I did not expect them to stay at 3.9V for close to 2AH of their capacity at a 18amp load.

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Re: Building A Ludicrous 14s2p SPIM08hp battery

Post by DogDipstick » Mar 23 2020 2:17pm

Lol I just had it out with Tom about these.


Apparently the new batch is testing much much better. Mine were from well over a year ago. Plus now he offers the cell holders.
Allota Watts @ 83.1v of raw QS power takes me everywhere on my Ironhorse DW link XC... :) Powered by Chevy. :D Broke 10 horses the other day. ( BTW; ...don't get hurt... :? )... (Currently building a battery datalogger.). :roll: Playin with (24) IRFB4115s now. :wink:

thorlancaster328   10 W

10 W
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Joined: May 25 2018 3:20pm
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Re: Building A Ludicrous 14s2p SPIM08hp battery

Post by thorlancaster328 » Mar 24 2020 1:41pm

The pack is almost completely built, all that's left is to add balance wires and shrink wrap (after a few tests on the bike). To join the cells, I used a torch and solder to tin each tab and join them together, and a pair of 14AWG solid copper wires (about 3/4" between each cell) to join the cells together. The wires were soldered to the tabs with ample amounts of solder. After soldering the cell groups together in series to make two 7s packs, I folded them accordion-style and taped them tightly together with fiberglass-reinforced tape. After building the two 7s packs, I joined them with a 2-inch section of 12AWG wire, capped them with fiberboard, and wrapped them TIGHTLY with more fiberglass tape and twine. To evenly distribute pressure across the face of the cells, I added 3-5 layers of masking tape on the ends of the cell faces with more towards the center.

I kept a wet paper towel on the ends of the cells during the soldering process to keep the cells cool, and the part where the actual cell begins never got too hot to comfortably touch. After adding a balance plug I'm looking forward to taking the pack for a test ride.

Picture of solder tinning on battery tab:
Tab Solder.jpg
Tab Solder.jpg (53.53 KiB) Viewed 156 times
Picture of (almost)-completed battery pack, less balance wires:
Entire Pack.jpg
Entire Pack.jpg (156.24 KiB) Viewed 156 times
Close-up picture of one cell connection:
Connection Close-up.jpg
Connection Close-up.jpg (113.67 KiB) Viewed 156 times
The pack is composed of 10 2p/16.5ishAH and 4 3p/24ishAH bricks. I did this to shore up some of the weaker cells; it's better to have strong outliers in the pack than weak outliers.

Right now, the pack is charging on my ISDT q6 charger, split into 2 halves of 7s because that's all it can do. To ensure maximum power, I'm balancing the pack while charged to 4.05 volts per cell. When discharged, the 4 3p groups will have some power left in them, but they will have only slightly less voltage than the rest (2p) when fully charged. Paralleling the weaker cells will also help keep the pack IR down.
Find weakest component, upgrade it, repeat until satisfied. Rome was not built in a day.
When in doubt, get bigger MOSFETs / Batteries / Motors / Etc.

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