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Questions on my 1st build
#1
New here and learning A LOT from these forums...
Most of my questions were answered but a few are still bugging me. In advance I appreciate your attention and time to reply to any of my questions.
Trying to build small battery pack 24V with 400-500w , few AC 110V plugs and ability to charge via solar (if not to complicated or costly).
So here are:



- 7s14p system with batteries in 1600-1800mAh (lower end/quality, bought from battery hookup site). Will this be OK for my build?
- On a system like this 1 BMS (24V 7s version) OR 14 BMS (24V 7s version)? Each series of 7 gets 1 BMS ?
- Is there schematic on wiring this 7s14p (battery pack to charger to shunt display to...) ?
- Trying to make this on a small budget. Are chinese BMS (ebay/aliexpress) OK for something like this?
- What would be good battery holding system that is solderless? 

Cheers
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#2
Generally your battery pack should have several cells in parallel per each "1s" section, eg (example) you'd be making a 7s5p with a total of 35 cells in 7 groups in series of 5 in parallel each group.

With this pack built structure, one 24V 7s BMS would connect across each of the groups of 5p.

Try your luck with am Ali/ebay BMS, but watch it & comfirm it's working correctly.

Gear usually comes with diagrams :-)
Running off solar, DIY & electronics fan :-)
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#3
So each of my 7s series would get 1 line to monitor from BMS ? In fact I need 24V BMS with 14(15) wires /leads of it...
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#4
a 7s battery pack will only have 8 wires to connect to the BMS for balancing. The bms you buy will usually show you where to connect all the wires. 


picture of 7s balance connector


Always double check that your balance wires are connected correctly before plugging into bms. I connected wires wrong before. I use a capacity checker to check they are correct but you can use a multimeter.

capacity checker can check up to 8s
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#5
(01-25-2019, 08:12 PM)mskip Wrote: New here and learning A LOT from these forums...
Most of my questions were answered but a few are still bugging me. In advance I appreciate your attention and time to reply to any of my questions.

I too, was once like you ... now time to pay it forwards and share some time with those that are starting out.   : )

(01-25-2019, 08:12 PM)mskip Wrote: Trying to build small battery pack 24V with 400-500w , few AC 110V plugs and ability to charge via solar (if not to complicated or costly).

a nice sized project to kick you off, great!

and that would be 400-500WH -- that's Watt-Hours.  

if you think of wattage (W) as speed of a car, then the capacity (WH) would be like the cars range.  both important characteristics, but completely different.  getting this thinking right will help you lots and lots on an ongoing basis.


(01-25-2019, 08:12 PM)mskip Wrote: So here are:
- 7s14p system with batteries in 1600-1800mAh (lower end/quality, bought from battery hookup site). Will this be OK for my build?

yes, thats fine..

(01-25-2019, 08:12 PM)mskip Wrote: - On a system like this 1 BMS (24V 7s version) OR 14 BMS (24V 7s version)? Each series of 7 gets 1 BMS ?

it will be much simpler and is standard practice to only use one BMS per string.

if its a 7s string then you need a (one) 7s BMS.


(01-25-2019, 08:12 PM)mskip Wrote: - Is there schematic on wiring this 7s14p (battery pack to charger to shunt display to...) ?

each setup is different in detail, but often similar in overall design.

by having a BMS, and running your dis/charge through that you will have a good layer of 'protection' from wiring faults.  by adding fuse/s you get another layer.

then follow your nose ... make more posts here ... someone will answer you, guarenteed!


(01-25-2019, 08:12 PM)mskip Wrote: - Trying to make this on a small budget. Are chinese BMS (ebay/aliexpress) OK for something like this?

we all like small budgets here!

I would say that the 'cheap' BMS's are ok for purpose ... IE something on the small side like you are planning.  one doesn't put Pirelli (great!) tyres on a Skoda (sorry owners!).  

Do note though that even ones that claim to have balancing function really ... don't.  Its only a top balance, and at <50mA at that.  So I recommend that you top balance your pack after (before??) construction with a proper balance charger and then connect the cheap BMS to do its thing.  It would be a bonus to get a BMS that has a removable balance lead/plug so that you can service and inspect this pack without any soldering or jumper leads etc.  But not essential..

Before connecting to BMS, check your wiring with a multimeter.  incorrect wiring may destroy other devices as they may not be designed to be connected to a miswired battery..


(01-25-2019, 08:12 PM)mskip Wrote: - What would be good battery holding system that is solderless? 

There are several of us doing solderless walls.  A search on the forum with the keyword "cartridge" highlights some of them.
--    ----    ----    ----    ----    ----    ----    ----    ----    ----    ----    ----    --
each Sunday (ish) I will be posting a fresh thread... describing my whole harvesting process. 
It's split up into nine phases.  stay tuned!
-----------------------------------------------------------------------------------
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#6
Thank you DCKiwi...
You answered my questions...for now
Cheers
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#7
There is a photo on reddit with a build that I would like to make.
What would other side be wired like?

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#8
(01-27-2019, 02:34 AM)mskip Wrote: What would other side be wired like?

nice ....

well, the answer for me depends greatly on your plans for this battery.  IE will it ever be stressed, at all?  even to 5A?

if not, then any way will work fine.

if it will be, or might be, or could be, or ... (you get the idea, do it right now, and then have an overengineered battery that you can repurpose at your leisure) ... then you should consider where/how the other side is relative to this side.

ideally you want the same toal length of busbar to each cell.  ---> add the length on the +ve side, to the length on the -ve side ....

now practically speaking, i do NOT say to measure anything.  but do think about it .... lets draw a 'picture', Ill try in text.


'in'
|
+------------------------------
      |       |        |
      1      2       3               <----------------- cells, in parallel
      |       |        |
-------------------------------+
                                        |
                                     'out'

see how each one has different length busbars, BUT they all have the SAME total length?  this keeps all cells locked into same terminal voltage, regardless of load etc.  otherwise the cells closer to the busbar interconnects (in/out here) get a much bigger workout than those far away.

so the 'in' and 'out' would be diasychained to the next series of cells, or the BATT-ve and BATT+ve if theyre on the ends of the daisychain.

hows that?
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--    ----    ----    ----    ----    ----    ----    ----    ----    ----    ----    ----    --
each Sunday (ish) I will be posting a fresh thread... describing my whole harvesting process. 
It's split up into nine phases.  stay tuned!
-----------------------------------------------------------------------------------
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#9
Doing a lot of reading on these forums. A TON of info on many topics...
My next question is 'bout charging this battery pack.
Solar controller charger seems to be the cheapest way to do (mpt7210a) but ... Will these solar contr.chargers step up or down voltage needed to charge my pack (29.4V)?
Amperage needed?

Many videos on ISDT T8 balancing chargers (2S-8S option) but it cost over 100 US$ and there is NO power supply to it (50-60 US$).
Any opinions on this way to charge and balance my pack?
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#10
(01-29-2019, 01:24 AM)mskip Wrote: My next question is 'bout charging this battery pack.

have you completed assembly ok? (pics please!)

do you have a regular balance lead attached ok?



(01-29-2019, 01:24 AM)mskip Wrote: Solar controller charger seems to be the cheapest way to do (mpt7210a) but ... Will these solar contr.chargers step up or down voltage needed to charge my pack (29.4V)?
Amperage needed?

a solar controller wont balance a battery.  for that, you need a balance charger.

that might be obvious, but you do go on to talk about one of my very favorites ...


(01-29-2019, 01:24 AM)mskip Wrote: Many videos on ISDT T8 balancing chargers (2S-8S option) but it cost over 100 US$ and there is NO power supply to it (50-60 US$).
Any opinions on this way to charge and balance my pack?

you are correct in saying that the T8 comes without an AC power adaptor.  I ended up getting an iSDT CP16027 (27V 6A) for field charging my electric skateboard from an AC socket.  But even that little beast (the AC/DC power brick) is only rated for 160W.

the T8 is rated at 1000W.  you really dont need that.  its real strength comes from a super strong balance hardware (2A!) and the firmware to match.  it is unlikely you need that for now.

the old SC608's were super ... but discontinued now.  the Q6 is ok, and the D2 is amazing.  perhaps you might benefit from a D2 until you get some serious DC happening on your workbench?

you could always do one 'bank' at a time, using CC/CV .... but that would be so painfully slow ... you could rewire them all into one giant 1s (not always possible) ... but really .. it easiest with just a regular balance lead on a hobby/balance charger if you can get one ...
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--    ----    ----    ----    ----    ----    ----    ----    ----    ----    ----    ----    --
each Sunday (ish) I will be posting a fresh thread... describing my whole harvesting process. 
It's split up into nine phases.  stay tuned!
-----------------------------------------------------------------------------------
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