18650 portable battery pack

albach

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Jun 17, 2018
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Hi guys i recently found my old Energie Station (german brand name form Einhell) which was a 50 Ah sealed Pb gel battery with a charger and some cigarette lighter outlets. I want to do a little water camping trip in the summer and wanted a small reliable energy source for charging my phone and cameras. the Pb battery is dead and now the question arose to replace it witch 18650 cells. I have a few 2p4s packs and 3 of them have the exactly same size a the pb battery.
My question is if i use the 2p4s cells and connect them in parallel i get 10v if they are completely (2,5v) per cell empty and 16,8 completely charged (4,2V per cell).
For a cigarette lighter output both is wrong. I also want to be able to charge everything off a 12v outlet at camp stations or my car.
My idea is to use one stepup converter so get 16,8V for charging to the bms and one boost buck converter to get 12 v to the outlets maybe also two one for each outlet.
is there an easier option or are my thoughts correct. I will put fuses in front of the outlets so hopefully only the will blow up in case of an overload or short. Charging is no problem because the cells already have a bms fitted to them
thanks for your help
Albach

edit 1
one further question i found the cells (cgr18650CG from panasonic) original data-sheet (http://www.meircell.co.il/files/Panasonic CGR18650CG.pdf) which specifies a 430mA continuous discharge current but also shows the discharge characteristics with 4.3 amps per cell on some onlinestores they specify them as 10 A cells but down in the specification max continuous discharge current is given at 430 mA

edit 2
i know that the original device (medical monitor) drains the whole 2p4s pack in 1 hour so it has to draw 10A corresponds to 5 A per cell
 
The older Panasonic datasheets don't explicitly state the maximum discharge current unlike others do. 5A is reasonable for this type of cell, it's definitely not a 10A cell.
 
Connection in parallel is fine.

Don't run them below 3V if you want them to last, same for charge, not above 16V, uunless you really need the extra few mAh.

Buck/boost for supplying your 12V will work fine, buck for USB charging,

Boost (step-up) unit for charging - be aware that most boost only units pass through the supply voltage if the load voltage is lower. i.e. if your battery is at 12V and you plug in the car at 13.2V (engine running, alternator on float) the 13.2V will pass through to your battery pack and any current limiting you have set in the boost unit will not work. Blown fuse... Buck/boost for charing..
 
completelycharged said:
Connection in parallel is fine.

Don't run them below 3V if you want them to last, same for charge, not above 16V, uunless you really need the extra few mAh.

Buck/boost for supplying your 12V will work fine, buck for USB charging,

Boost (step-up) unit for charging - be aware that most boost only units pass through the supply voltage if the load voltage is lower. i.e. if your battery is at 12V and you plug in the car at 13.2V (engine running, alternator on float) the 13.2V will pass through to your battery pack and any current limiting you have set in the boost unit will not work. Blown fuse... Buck/boost for charing..

Thanks for your answer. what do you recommend for boosting the voltage for charging from 12 v i do not have room in the case for a dedicated dig li ion charger. but if i dont current limit the DC and the voltage drops a bit it only means th battery will not get charged fully in the most case
 
I like the units that are listed as "1200W boost" on eBay and Ali becuase they can also be set to stop if the source voltage drops below a certain level. The are effectively non tracking solar boost units.
These ones (many different sellers) : https://www.aliexpress.com/item/DC-...oltage-Power-Supply-IN-8-60V/32835019014.html

Alternatively the 10A 800W boost units can work ok like this one : https://www.aliexpress.com/item/Hig...ly-600W-DC-DC-10V-60V-to-12V/32608442360.html

The boost units must have at least 2 of the blue adjustable pot resistors (one for voltage and the other for current) if they have a 3rd one then this is usually for setting the minimum input voltage level, MPPT style.


This one might work ok, but I doubt it would not deliver 10A for any amount of time without setting on fire.
https://www.aliexpress.com/item/DC-...supply-250W-10A-LED-Driver-W/32664665347.html


This one seems better for the price, with heatsinks.... should run at 8A ok.
https://www.aliexpress.com/item/400...ant-Power-Supply-Module-8-5V/32817074597.html
 
Sorry for the delay, part way through the response and my internet connection went down...

Those units are boost only, so ok if you are charging from 12V or a lower voltage than your battery pack....
Will find the links for buck boost units. The buck/boost usually have two coils / inductors visible.


This is small current (2A) and from your pack layout (4P) I'm guessing a maximum charge rate of 4A ? Two of these could be used, or...
https://www.aliexpress.com/item/LM2...ltage-Power-Converter-Module/32785440068.html

Something a little larger with a display on (6A)
https://www.aliexpress.com/item/New...-Module-Boost-Buck-Converter/32810174624.html

2A MPPT style that could be used with a solar panel (3 adjustment pots : output voltage : output current : min input voltage)
https://www.aliexpress.com/item/LM2...ltage-Power-Converter-Module/32849911953.html

Probably find this cheaper as it is 7A capable and a good option
https://www.aliexpress.com/item/Aut...V-10A-80W-Adjustable-Voltage/32510686551.html

Hopefully those will give you an idea as to what you need.
 
ok thanks i had another idea of using a small b6 style charger which could handle balancing and charging and boosting the voltage at the same time because you can input between 6 and 36 volt i just don know if i have to disconnect the balance leads from the charger when i discharge the battery or not.
https://www.banggood.com/de/SkyRC-i...4-p-929890.html?rmmds=search&cur_warehouse=CN
something like this one where i could easily control the max voltage as you recommended. then i just need a discharge protection i thought of this circuit from DIY Perks
 
With the B6 it will adjust the current to balance correctly without any need to cut-off upper charge voltage adjustments.
You can leave it connected if needed, the reverse current would be minimal.

You could always use a cheap chinese BMS unit purely for the disconnect protection and have a separate volt meter or battery charge indicator so that you can see the battery state before it get's too low....
 
Preferences have to be your own.... I'm biased for my own reasons... :D
Your choice is :
B6 : will work, charge the pack well and balance it, add a BMS to prevent over discharge and a meter. clear and reasonably simple.
DC DC : Lot more work, save a few , learn a bit more in the process. would need to understand a BMS fully (balancing current issues)
 
Ok I think I will stick with the b6 version for charging and a cheep under voltage protection because if you add the BMS and the DC DC regulator and my labor up creating everything shorting something out and starting from scratch all over the b6 is more easy and if it breaks down I can replace it in the future. It was my intention to include a small voltmeter onna pushbutton to check the battery voltage. I will make a build log on the forum and thanks a lot for your time and help I was on a lot of other forums where I had no responds (all about circuits and the eevblog forum)

Albach
 
May I bother you with another question: what is the best way to connect the packs in parallel to each other. I would charge everything withe the balance charger to maximum an then measure each pack has the same voltage and then connect them in series as well the balance leads for the b6 charger
 
You could make up some balance leads that connect the packs in paralell and charge them up together. Depends on how your packs are setup/wired and conectors. Or just hard wire all the packs together.

Do you have any pictures or examples of the packs ?
 
Those are the packs


image_coihqn.jpg

image_aggpva.jpg
 
If you want to connect those in parallel, just take an connect another lead to your balance leads (the red, yellow, white, etc) and have a female connector on one pack, and a male connector on the other. Then just connect them up to make them parallel.
Please note that both packs needs to be almost the same voltage cell for cell before connecting. They needs to be <1V off. So, parallel cells connected at the red of pack 1 needs to be <1V difference than parallel cells in pack 2, same with cells 2 - 4. Otherwise, you could end up with very hot wires connecting the packs together.

If you want to make them into 1 pack, just lay the two packs together, pull solder the parallels together with some short wires and use the existing balance leads of one pack. These would need to be about 18awg or larger as they will be handling some current into the other pack. The other pack you'd rip all the wires off.
Use the metal tabs to know where to bridge the cells together.


image_ezowoj.jpg
 
Thanks for your reply to bring you up to speed I want to connect 4 or 5 of those packs in parallel. The charger I want to use has a balancing current of 1 A so do the balance leads do not have to handle more than one amp.
I was worrying most about how accurately I have to mach the batteries before connecting in parallel but if <1 V is good enough it should be ok if i charge them all fully and then connect them. For the main leads i wnated to use 3.5mm^2 wire between 13 and 14 awg (for 50 Amps, 0.5 m, 3% voltagedrop and copper wire equals to 2.89mm^2). For the balance leads 1mm^2 17 - 18 awg because they only will get 1 amp at the maximum
these are the specifications for the charger weightiest disadvantage it will take 15 h to completely charge the pack but it fits nicely into an existing compartment in the case

Brand Name: Charsoon
Model: DC-4S
Item Name: 2-4S Li-poly/Li-ion Battery Balance Charger & Voltage Detector
Operating Voltage Range: 9V-16V DC
Operating Temperature: -20-45&#8451;
Cells Type Supported: 2-4 cells Li-lon/Li-poly
Input Power Request: Recommended 30W
Max Charge Power: 25W
Charge Current: 1500mA
Charge Accuracy: 10mV
Balance Current: 1000mA
Display Accuracy: 10mV
Size: 81mmx50mmx20mm
Weight: 95g
 
Just line all 4 or 5 packs up and connect them as Korishan indicated.

The balance leads may only need 1A for balancing but if there is any issue with cells in the future you may find the balance/inter pack flow starts to rise above 1A during charge / discharge. This may be a long time off but preparing for the worst can save hassle in the future. 1mm for balance is good.

Full charge, check and check again the voltages and the connect. Check each cell to cell point. I would go for <0.5V as I get over 10A with a 1V difference, but my pack is a little different.

I would go with 4mm minimnum for 50A or use 2 x 3mm if that is the cable you have. 3mm will get warm/hot. 50A from a pack that size may cause some of the other parts to get warm depending on the cell to cell connections, plus 50A on 5 parallel packs is 10A per cell discharge and is a lot to pull for a small pack.

What is the component on the left of the image / last cell - is that a thermal fuse or temperature sensor ?
 
That little device is a thermal fuse. I find them in some of the packs. Not all, though. I recognized it when I zoomed in on the image.
 
Ok, then I will look for 4mm^2 wire. 3.5mm^3 was my first idea because it is used in 3 phase household appliances so it is very cheap and available.
@completelycharged if you talk about wire do you measure the cross-section or just the diameter all those units are confusing mm^2, mm and awg. Yes, it is a thermal fuse and there is another one in the bms. I want to reuse the thermal fuses in the pack to connect the individual small packs in parallel to each other as a safety feature.
now I just have to wait until my charger arrives and then I think I am able to start the build.
 
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