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Registered Member #580
Joined: Mon Mar 12 2007, 03:17PM
Location: Melbourne, Australia
Posts: 410
from the batteries perspective, is it safe to use these 5 3.7v 1.2Ah lipo cells if i connect them all in parallel for both discharge at 9A into this and to charge them at 1A by this. I do specifically mean those ones at the ebay link to ensure they are the same, not 5 random ones i may have that are the same type as that link.
Is there any safety concern with the batteries if connected in parallel, with the above usage?
Separate question: I can't seem to find any datasheets for "CA148" so I wonder of the cells have any sort of inbuilt protection?
Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
I don't have any experience with lipo cells yet, but, i don't think that there is anything to worry about with using batteries in parallel (assuming that they are the same.) The main issue with using multiple batteries is when they are placed in series, because they are not an ideal emf source and hence have an internal resistance. That resistance turns some of the energy flowing across the battery into heat, and if multiple batteries are in series, then the energy from the first must pass through the second, increasing the heat dissipated in the second. Too many batteries in series demonstrate the need for the "do not dispose of in fire" label. If you have multiple batteries in parallel, and they have approximately the same internal resistance, then they should share the current passing through (well, being created by i guess) them evenly, resulting in the same amount of heat in a given battery as if it were connected by itself. From what i have heard about lipo batteries, they can be fickle about charging and express their discontent via flames and toxic fumes, so i'd look into a charger especially designed for that type of battery.
Registered Member #191
Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720
It will be fine, the 5P module will be charged at 1/6C and discharged at 1.5C. However, you are going to need a circuit with a driver for the LED and a low cell voltage cutoff, between the cells and the led.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Yes, paralleling them is fine, just make sure they're all in the same state of charge before hooking them together for the first time, and then keep them together. (I have a 7.2V, 160 watt-hour "brick" of LiPos like this.)
The batteries have no internal protection: RC model ones never do because it gets in the way of the desired high current drain. So, your LED driver will need an undervoltage shut-down. (The RC models have it built into the speed controller.)
The charger should be fine, as it's designed for Li-Poly batteries, and that's what you've got.
All said and done, it'll be no more dangerous than driving a RC car with the same batteries.
Registered Member #580
Joined: Mon Mar 12 2007, 03:17PM
Location: Melbourne, Australia
Posts: 410
Is there some trick with the shutdown? a simple comparator my trigger as the load is turned on (if i PWM it) or or may oscillate like wild as the battery drains
Registered Member #509
Joined: Sat Feb 10 2007, 07:02AM
Location:
Posts: 329
Latching would be the best, a lot of hysteresis would work too. I.E. off at 2.7-2.8v (under load) and back on at 3.4V
3.4V open circuit in a Li-Po battery would have not much capacity left in it, so if it shuts off at 2.8 under load and recovers back to 3.2-3.3v it should stay off till you charge it.
But as stated, you need some sort of driver, and I dont know of any single Li-Ion cell SST-90 drivers, quick and dirty would be 24-25 AMC7135 chips in parallel. Power dissipation for those wouldnt be that bad since the Vf of the LED matches the Vf of the battery back fairly well, and their dropout voltage is fairly low for after it comes out of regulation.
If you would run a 2S pack, there are efficient buck drivers which would work for you, but you would still need a low voltage cut-off, and a balance tap to charge it how you would an RC-car pack.
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Is this battery configuration safe?
