Another Charging Question
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Ahh, thanks for clarifying that on the darwin. I had seen posts stating that it were 2x 1200mah batts in series from when it was first in testing. It's hard to find information on it seeing as google mostly brings up results for darwin the person 
no matter how I phrase it. And it puzzled me how it could have that kind of circuitry in such a small package.
Liking the quote, mr madman. Tesla was the man! Watched the whole history channel documentary on him. It's crazy how some of his ideas are only recently coming into fruition - wireless power.
no matter how I phrase it. And it puzzled me how it could have that kind of circuitry in such a small package.Liking the quote, mr madman. Tesla was the man! Watched the whole history channel documentary on him. It's crazy how some of his ideas are only recently coming into fruition - wireless power.
Going off topic, but yeah, Tesla's wireless power was in the same vein as Einstein's unified theory. They both spent the majority of their later years working on their follies without much coming to fruition. Though both ideas are a holy grail of sorts, one for physics and the other for electrical engineering.
Back on topic, the only issue with LiPos as far as safety is they are not typically protected and with their low internal resistance, they can dump a lot of current if shorted. If you add the necessary protection, they really are no more hazardous than any other Li-Ion. They've been used for years in cell phones and digital cameras, though they have not been free from incident.
Back on topic, the only issue with LiPos as far as safety is they are not typically protected and with their low internal resistance, they can dump a lot of current if shorted. If you add the necessary protection, they really are no more hazardous than any other Li-Ion. They've been used for years in cell phones and digital cameras, though they have not been free from incident.
meh...each to their own...My issue w lipos is their sensitivity to being deformed and how easy it is to deform them...inside something...well they are only as tough as whatever they are encased in...but back on subject...U couple have your questions been answered?
Any of u guys know of a decent balancing li-ion/polymer charger? Dont need anything more than 2s but it would be nice to be able to in the future. I gave away my wf-188 to a friend in need and am looking to get something advanced I can rig something external to charge 26500's, 18650's, etc.
This one is inexpensive and has a 650mA rate so you can use it on round cells too.
HobbyKing R/C Hobby Store : Turnigy 2S 3S Balance Charger. Direct 110/240v Input
HobbyKing R/C Hobby Store : HobbyKing E4 Balance Charger
I got the second one because you can set the charge rate.
HobbyKing R/C Hobby Store : HobbyKing E4 Balance Charger
I got the second one because you can set the charge rate.
Thanks for the suggestions - I'm also willing to spend more for more features that could come in handy. Such as measuring a battery's internal resistance, safety features, multiple chemistry charge
HobbyKing has great prices, but you have to pay attention to where it's coming from. They have warehouses all over the world with their main warehouse in Asia. If it ships from overseas, it can take a while to get your order.
There's a large range of chargers on the HobbyKing site. If you want more features, you should be able to find one within your price range.
There's a large range of chargers on the HobbyKing site. If you want more features, you should be able to find one within your price range.
Just a quick comment to Craig (Best Regards BTW 
) You CAN charge dual series anything cells off USB - been done over and over again.
Obviously, there is a bit of skill involved - Just endeaver to the challenge and yee shall find....
Mcgyver
) You CAN charge dual series anything cells off USB - been done over and over again.Obviously, there is a bit of skill involved - Just endeaver to the challenge and yee shall find....
Mcgyver
Note: The above post was in reference to the above comment - IE: There would not necessarily be a need "to pull cells out of series" ....
But if you want to - that's OK with me
Yes, there's a way to use USB to charge a pack without taking the cells out of series. A boost regulator can be used on a USB supply to increase voltage high enough for a pack charger. However, that would require some rather complicated circuit design, PCB layout, and assembly. That's not something most people can do.
It might be possible to do it in a modular fashion. In other words, wire up a USB receptacle to a boost regulator to a pack charger, but that's a lot of space required inside the mod.
Without building a PCB yourself or utilizing something that takes up a lot of space, switching the cells in and out of series with a couple USB charger boards is the most do-able thing I can think of.
It might be possible to do it in a modular fashion. In other words, wire up a USB receptacle to a boost regulator to a pack charger, but that's a lot of space required inside the mod.
Without building a PCB yourself or utilizing something that takes up a lot of space, switching the cells in and out of series with a couple USB charger boards is the most do-able thing I can think of.
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I'm thinking of trying this. Run two Series batteries for mod operation and charge two Li-Po batteries in parallel w/ a USB single charger circuit Perhaps it will take twice as long being it charges at a rate of 500mA.
The circuit will place the Li-Po's in series (8.4v) when the 3.P.D.T. switch is in the UP position and the Li-Po's will be in parallel with the 3.P.D.T. switch is in the DOWN position which also places the USB charger on line.
The circuit will place the Li-Po's in series (8.4v) when the 3.P.D.T. switch is in the UP position and the Li-Po's will be in parallel with the 3.P.D.T. switch is in the DOWN position which also places the USB charger on line.
That should do it.
I would do one thing different. I'd place F1 in series with LiPo1. That way, you still have over-current protection regardless of how the cells are wired and the USB charger will see matched impedance on the cells. That allows them to charge in a perfectly balanced manner.
You can get a USB charger board with a 1A rate. They are available, Adafruit has them. A 1A rate will preclude you from using a data USB port, but you can use a charging port no problem (wall wart or other charging adapter). The USB 3.0 spec says charging ports can go up to 1500mA. If you're planning on using the 1000mAh 20C LiPos, they have a 2C max charging rate which is 2A. With two cells in parallel and a 1A USB charger, that will be 500mA to each cell so you're only using a 1/2C rate, well within tolerance for the cells.
I would do one thing different. I'd place F1 in series with LiPo1. That way, you still have over-current protection regardless of how the cells are wired and the USB charger will see matched impedance on the cells. That allows them to charge in a perfectly balanced manner.
You can get a USB charger board with a 1A rate. They are available, Adafruit has them. A 1A rate will preclude you from using a data USB port, but you can use a charging port no problem (wall wart or other charging adapter). The USB 3.0 spec says charging ports can go up to 1500mA. If you're planning on using the 1000mAh 20C LiPos, they have a 2C max charging rate which is 2A. With two cells in parallel and a 1A USB charger, that will be 500mA to each cell so you're only using a 1/2C rate, well within tolerance for the cells.
I was planning to install a LiPo Charger which I had. http://www.sparkfun.com/products/10217 Installs inside the mod. It's output is 500mah. So that would be 250mah per battery. Is that okay for a 20C lipo? I was thinking charging would be slower but feasible.
I have an F2 fuse shown in the schematic which is in series with the two Lipos. Is that what you meant Craig?
I have an F2 fuse shown in the schematic which is in series with the two Lipos. Is that what you meant Craig?
Here is the charger I was talking about. It's based on the Microchip MCP73833 charge management controller which is the same controller I use in my own mods. It's a very nice full featured controller, programmable to 1 Amp.
20C LiPos typcially have a 2C max charging rate. 1C is perfectly acceptable so for a single 1000mAh 20C lipo a 1A rate would be fine. Using two cells in parallel would split that rate in half so each cell would be charging at 1/2C. BTW, a 1C charging rate always works out to one hour. A 1/2C rate is always two hours. Though, charging is not 100% efficient and current drops down when the charger gets to constant voltage mode toward the end of the charge cycle so a 1C rate works out to around an hour and a half in reality. A 1/2C rate would be more like two and a half hours.
With respect to the fuse, I mean the F1 fuse shown in your schematic. I would relocate it in series with the number one LiPo cell so each cell has a fuse on it. A 20C 1000mAh LiPo can handle 2A input current continuously from the other cell so you can probably get away with something around a 3A trip since the cell only has to endure that current for the time it takes the fuse to trip. The trip current spec for a PTC fuse is misleading. They trip at any point above the hold current, it just takes longer.
You'll have to take a bit of an efficiency hit since PTC fuses with a lower trip current do not have particularly low resistance. You'll want to select the lowest resistance you can. You will also be limited in output by the fuses.
That's the advantage of using two charging boards. It allows you to avoid connecting the cells in parallel which simplifies things.
20C LiPos typcially have a 2C max charging rate. 1C is perfectly acceptable so for a single 1000mAh 20C lipo a 1A rate would be fine. Using two cells in parallel would split that rate in half so each cell would be charging at 1/2C. BTW, a 1C charging rate always works out to one hour. A 1/2C rate is always two hours. Though, charging is not 100% efficient and current drops down when the charger gets to constant voltage mode toward the end of the charge cycle so a 1C rate works out to around an hour and a half in reality. A 1/2C rate would be more like two and a half hours.
With respect to the fuse, I mean the F1 fuse shown in your schematic. I would relocate it in series with the number one LiPo cell so each cell has a fuse on it. A 20C 1000mAh LiPo can handle 2A input current continuously from the other cell so you can probably get away with something around a 3A trip since the cell only has to endure that current for the time it takes the fuse to trip. The trip current spec for a PTC fuse is misleading. They trip at any point above the hold current, it just takes longer.
You'll have to take a bit of an efficiency hit since PTC fuses with a lower trip current do not have particularly low resistance. You'll want to select the lowest resistance you can. You will also be limited in output by the fuses.
That's the advantage of using two charging boards. It allows you to avoid connecting the cells in parallel which simplifies things.
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