How to rebuild a duct tape LiFePO4 Battery

[biketrials]

comments welcome...

must-read for battery newbies

 

[docnjoj]

Thanks Biketrials! That really helps!
otherDoc

 

[dogman dan]

I hope not to need this, but you know someday i will! THANX!

 

[Mark_A_W]

Hey, where in Oz are you biketrials?

 

[swbluto]

Thank you! I'm also a soldering newbie, so the part on de-soldering was particularly helpful. I was ready to just cut off the existing foil tabs and solder on the new ones!

 

[hippiehunter]

So in reading this it seems to say that you can run ping packs in series if you use a diode? Im very surprised to have not heard this before as it would be very nice info to have had a few months ago. Can anyone else confirm that im reading this right?

 

[swbluto]

So in reading this it seems to say that you can run ping packs in series if you use a diode? Im very surprised to have not heard this before as it would be very nice info to have had a few months ago. Can anyone else confirm that im reading this right?

Please see post #5 of Fechter's topic "Series and Parallel" http://endless-sphere.com/forums/viewtopic.php?f=16&t=1312, which is categorized under the forum "EV Basics" which itself is categorized under "Electric Vehicle".

 

[hippiehunter]

Ive been looking around on the forum but I can really seem to figure out why people use Schottky diodes with 2 anodes and a common cathode. Right now my only experience with diodes has been the tube kind, with one wire on one side and one wire on the other. As far as I can tell from the diagram in the PDF there is one wire going into the diode and one wire going out, what am i missing? And in my case im combining 2 36v batteries and I expect a max of 40 amps. Does that mean I need a 50v 50amp diode or a 100v 50amp diode?

 

[swbluto]

Right now my only experience with diodes has been the tube kind

Right now my experience has been the virtual "Circuit simulator" kind.

Which means, I don't know.

 

[fechter]

Ive been looking around on the forum but I can really seem to figure out why people use Schottky diodes with 2 anodes and a common cathode. Right now my only experience with diodes has been the tube kind, with one wire on one side and one wire on the other. As far as I can tell from the diagram in the PDF there is one wire going into the diode and one wire going out, what am i missing? And in my case im combining 2 36v batteries and I expect a max of 40 amps. Does that mean I need a 50v 50amp diode or a 100v 50amp diode?

You can use 50v. The diode only "sees" one pack.

The dual diodes are generally more available and cheaper. You can put both halves in parallel to get twice the current rating. They are easier to mount on a heatsink (if needed). The leads break off real easy too, so mount carefully. The shape of the diode doesn't really matter.

 

[hippiehunter]

Ive been thinking about it and I now am interested to find out if i really need much in the way of continuous amp rating on the diode. Clearly the diode has to be able to withstand the voltage of one pack, but the reason im thinking of for not needing the diode to handle much current is that the controller will shut down at lvc anyway. Granted for those folks who dont have programmable lvc's this could still present a problem but in at least my particular case im thinking that i could get away with something like 3.5amp continuous with 125amp burst since it will only be a split second before the controller shuts down. Let me know if ive made any poor assumptions.

As a side question does anyone know what the difference between continuous and burst is in diodes? If its just a heat issue then building this thing into a heatsink would bring the continuous closer to the max?

 

[biketrials]

Mark_A_W: I'm in Perth

hippiehunter: If one pack cuts out then yeah you would turn off and re-start, so continuous rating is not so important.
The diodes I used came in a To-220 package which is the same package as the FETs in most controllers. 2 outer legs are connected together, and the middle leg and body lug is the other terminal.

 

[QwertyAccess]

right now i have a 48V Lifepo4 pack, how would i series a 24V lifepo4 assuming same AH rating? Where and what kind of diodes would I want? Looking at the diagram it looks like I have to connect diode between the + - of a pack?

 

[JinbaIttai]

I'm surprised this one isn't a sticky. Thanks for the guide!

 

[AussieJester]

Mark_A_W: I'm in Perth

WooT another Perthite! What suburb mate im up in Lesmurdie?`
Looking to organise a group ride in near future if your interested? we have a handful
of Perthites on the forum. Check in here if interested

KiM

 

[biketrials]

I'm surprised this one isn't a sticky. Thanks for the guide!

Cheers mate!

 

[amberwolf]

Does anyone have a copy of the OP's PDF file? the attached one is trashed, and I was hoping to link it/upload it in the ES Wiki.