YAPiP - recreating pEEf's approach

I'm buying re-configured packs from Enginer. Price of $900 for 24V80AH plus $100 for reconfiguration to 48V40Ah. I'm buying 4.5 packs. The half pack will be in the normal size container but only containg 24V40Ah cells and extra space filled with a suitable inert filler.

Bear in mind that this is for an assembled, tested pack with cell voltage leads and thermal probe housed in a battery box. How much would you charge for a similar assembly with the cells that you recommend?

I'm committed to this course (the check is in the mail) - but also I still think it's the right course for my particular needs and wants. I'll just have to wait and see with regard to voltage sag - but, as you say, there's a relatively straightforward fix for that (more cells).

BTW - just to make sure we're comparing apples-to-apples the pack is made up of these cells: F20-08180225. Is that the same cell as in your packs?

 

It might be an interesting process to figure out what you'd need to charge for an equivalent, assembled pack. Or not I'm not trying to be a PITA - just trying to get a feel for the value of assembly, packaging and testing for the different cell solutions.

Yes, I'm enjoying working with Jack - he's been very responsive to all my questions.

I take full responsibility for how I decide to use the cells and how well they perform. If I abuse them it won't be Enginer's fault

 

What a horrible picture!!

Hmm, that is worse performance than I'm expecting - so I guess I'll need to budget for some more cells (and more BMS, and more charger). I've attached the discharge curve from the RF spec sheet. It shows a 1C nominal of ~3.15V and a 3C nominal of ~3.0V (the big ugly lines are ones I added to determine the approximate nominal).



Oh well, it won't be the first time a spec sheet has been "optimistic"...

(but on the flip side Jack says the real capacity is more like 26Ah rather than the advertised 20Ah).

I did look at the miniBMS - but I'm planning on using Current Motor's BMS.

 

I think that would be an excellent idea. More data is always good. And cells tested by the same people using the exact same equipment and test methodology would be fantastic.

Edit: BTW, I don't doubt that the A123 cells are better in a lot of aspects than the RFE cells (the only non-contended attribute is that the A123 cells have less capacity than the RFE - although usable capacity may be open for debate). It's a question of cost/value analysis - do I need the better cells or are the cells I've chosen adequate for my usage? Data will help to quantify the old adage "you get what you pay for".

 

Yeah, that's a shame. Is the 10+C rating a continuous rating? I couldn't find a clearly spelled out continuous vs. peak rating for the A123s (but I didn't look very hard!).

However, your results highlight exactly the sort of thing that I'm talking about. I don't need 5C, I don't even need 3.5C continuous. In an ideal world I think I'd need a 3C continuous rating for sustained high speeds and only a 3C peak for suburban speeds. So, why spend money to achieve something I don't need? That's not a facetious question because there's certainly truth in the fact that if I use a 10C capable cell at only 30% of it's capability I'll get more life out of it. But that amount of life isn't quantifiable from the data you give and, with the greatest of respect, unless you're buying A123 cells from A123 then all bets are off in regards to them matching the spec sheet so even if it says it in A123 literature it needs to be seen with the cells you're actually sourcing.

BTW, I'm trying to separate the two questions: (1) Are A123's more than I need? & (2) Are RFE's going to be adequate or will they turn out to be a false economy? The questions are certainly related because it might be that if RFE's are a false economy then A123s and other more expensive options are back in contention.

The question I'm not trying to answer is "Are A123's better than RFE's?" That answer is simple: "Yes".

So, I think a useful test would be a 2C and a 3C test of both cells measuring voltage sag and temperature rise for those tests. These rates are useful for me because I'm planning a 40Ah pack. If you're planning a 20Ah pack then the higher C rates that you use are much more appropriate. For my pack 2C = 80A draw and 3C = 120A draw and my guesstimate (and supported by "the flan man" and pEEf) is needing slightly north of 100A for sustained high speed - of course the problem is compounded by sag because at a lower voltage I'll need higher current to give the same power.

If you'll sell me a single A123 cell and I can find a convenient source for single RFE cells (Jack only wants to sell packs - which makes sense) then I'll do that testing...

This is interesting conversation and I'm enjoying it. But, the check is in the mail, yaPIP will be starting life with a 72 cell RFE setup. What it evolves into is anyone's guess!

Peace, love & plug-ins (tm).

 

Thanks and good luck with Green Drive Expo.

 

Flaninacupboard : You don't like coding? Oh dear, poor misdirected man ... (yup to each their own!)

Good point with incrementing CDL. I do plan on logging and real-time visualization - both CAN data and raw data from the sensors. So I should be well setup for seeing the effects of my changes. The RFE data sheet lists charging rates of 0.5C (Standard) and 1C (quick). But I guess if we can't believe the discharge info then we should be leery of the charging info as well.

BTW, my BMS solution can easily (and cost effectively) add another 6 cells (we sell a 24 cell and a 30 cell bike - the 30 cell bike uses the 24 cell BMS plus a 6 cell expander). I'll also make sure that I buy a charger with enough headroom - so adding cells shouldn't be a problem. Although I will need to source them - but I'm sure Jack or Eric can help me out there.

BTW - a very important question: What's with the name flan-in-a-cupboard? There's got to be a story there!