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Here's my solution to charging multiple batteries at once:

DIl6VGJa


0ki4VTnu


uEMXs7nu


I am using 5 DC-DC 250W boost converters to which I have attached heat sinks. Each one is set to 95W - which means batteries are charged at just over 1C. It is faster than the 3DR wall plug and, most important, I can hook it up to the car battery and use it on the move.
The battery connectors are a mix of 3d printing and cutting copper blades. Quite a lot of work went into making them.
I might add some metal mesh on the sides to protect the electronics, but for now I am just careful with where I place it.

I hope someone will find this useful.
Cheers!
 
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Nice. I like the way you attached them all together. Very simple way to keep it neat and secure without elaborate cases or a box.
 
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That's awesome! I've only got one battery at this point (2 more on their way thanks to the sale this weekend). But, I was hoping to come up with something like this when I got multiple!
 
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Well, I don't see myself traveling with that thing on my suitcase, but for sure it will work wonders at home!:)
 
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Very nice! Looks like you connected the boards together using a threaded rod with tubular spacers, correct?

Also, where did you get the heat sinks?
 
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Here's my solution to charging multiple batteries at once:

DIl6VGJa


0ki4VTnu


uEMXs7nu


I am using 5 DC-DC 250W boost converters to which I have attached heat sinks. Each one is set to 95W - which means batteries are charged at just over 1C. It is faster than the 3DR wall plug and, most important, I can hook it up to the car battery and use it on the move.
The battery connectors are a mix of 3d printing and cutting copper blades. Quite a lot of work went into making them.
I might add some metal mesh on the sides to protect the electronics, but for now I am just careful with where I place it.

I hope someone will find this useful.
Cheers!
How much current does this draw when charging from a car battery? Will a car battery supply enough "juice" to charge 5 at once?
 
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Heat sinks are part of the CC/CV converter. I run 6 converters off of the car battery. Yes it will charge them all - if your car is running.

As far as how much current they draw - it depends on what you limit the current to per converter multiplied by how many converters you are running together. Personally I run mine at 6A, which would be 36A PEAK for 6. However, that is peak. You will only reach 6A draw from one if the battery is totally depleted (10% or below), and then the amp draw goes down from there as the battery charges until it reaches like 200 milliamps and shuts off, at which point it's charged. If the battery is at like 50% and you start charging, the amp draw might start out around 4 amps and not 6.

So what I'm saying, is you would rarely draw the max, and if you did it would only be for a very short time as the amp draw lessens as they start to charge. To see what I mean look at the battery charging graphs I created using actual battery data in this thread. You'll see that after 30 minutes of charging, the amp draw only goes down from 6A to about 5.3A. Then from 30 mins to 45, it goes down quite quickly from 5.3A to 3.3A. Battery Charging Graphs

You'll see the amps (the red line) going down over time as the voltage rises. You can run your mouse over the lines to see the actual data readings.
 
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How much current does this draw when charging from a car battery? Will a car battery supply enough "juice" to charge 5 at once?
With regards to the power draw, each converter draws max 95W. To charge the battery at 1C you need 5.4A at 16.8V, just over 90W. The circuit has a 95% efficiency, therefore it will draw around 95W from the source. At full power, the multi-charger will draw max 475W. You also need to factor in the cable resistance, so use good quality cables and keep them short. The maximum dram from a cigarette lighter plug is 120W. I am running a separate circuit from the car battery using 8AWG cables. I have a Nissan Pathfinder with a big battery and alternator and it copes just fine, but I can imagine you can run it on smaller cars too. If in doubt, buy a voltage meter and keep an eye on the car battery.
With 5 batteries and this charger, you can fly all day long as you keep rotating the batteries.
 
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Wow. Great job.
If you ever consider selling these on Ebay or something, I would be the first one to buy it! :)
 
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Wow. Great job.
If you ever consider selling these on Ebay or something, I would be the first one to buy it! :)
Thanks, I appreciate it. I took this project out of necessity, because there is no readily available solution on the market. You are not the first one interested in buying one. How much would you pay for something like this?

I hope my design and solution will help others to build their own.

Cheers!
 
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Thanks, I appreciate it. I took this project out of necessity, because there is no readily available solution on the market. You are not the first one interested in buying one. How much would you pay for something like this?

I hope my design and solution will help others to build their own.

Cheers!
Just FYI, there is (or was) somebody selling the same thing on eBay- stole the design from @PdxSteve. Don't remember the details.
 
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How much would you pay for something like this?
Cheers!

I don't know really but around 150$ sounds reasonable. No idea how much you spent for all the electronics though (and your time :)
 
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Awesome stuff, do you have links to the parts used?, Id love to build something similar
 
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Been meaning to post this for awhile. Big thanks to those on here that paved the way and shared their experiences and valuable knowledge. I put the boosters in a $5 project box from RadioShack along with a spare computer cooling fan. The fan works great and the plastic box is hardly warm to the touch while the exhaust is noticeably hot so no fear of a meltdown at all. The battery leads are removable to eliminate shorts when not charging all 4 batteries. Ran out of xt connectors but those bullets will be replaced when I get more and going to clean up the cooling ports some more as well. Made leads so it can be powered direct from a car battery, workbench power supply or car accessory outlet. My car only has a 20amp fuse for the acc port so I only charge 3 at a time when driving to be safe. It's working great!
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