Paralleling packs with a protection diode?

rg12

100 kW
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Jul 26, 2014
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Is there a simple way for protecting the parallel procedure of two identical packs that are paralleled while at different SOC voltage?
I know that some lead acid guys do something with diodes for that and didn't really understand how a diode would help.
I want to prevent or slow down the charging of the lower voltage pack from the higher voltage pack.
 
larsb said:
Sure, put a diode with a low voltage drop on the discharge line as protection against inrush/charging by the other pack. Connect additional separate wires to each pack without diode for the charging.

Ahh awesome! didn't know it's that simple, thanks!
 
You pulling a Louis Rossman?
He did diodes on UPP packs.
Check out the story on his channel.
I dont know the story, but he was doing 2 packs in parallel to increase ah/wh but rectifier or diodes or something.

I just unplug the empty battery and plug in the full battery, but I am 36v and 48v.
I would do it exactly the same way if I had two 48v batteries.

Extra failure modes you seem to like.

It all makes more sense now, not worth it. Get a new charger! :thumb:
Where you at now and where do you want to go, for charging rates etc.
I want to prevent or slow down the charging of the lower voltage pack from the higher voltage pack.
 
larsb said:
”louis rossman” (whoever that is?)

Rossman is a Youtuber, Electrical repair man. He is somewhat skilled in electronics, has a youtube channel, and a big following. I have watched a few of his vieos, and do not really like the dialog. The dialog is boring to me, with my skill set. Caters to limited repair knowledge, but he has carved out a spot in the world of electronic repair. I do not think he has any classic engineering training nor classic electronic engineering training. I do not think he is certified or licensed to engineer.

He made a vid when he caught some ebike batteries on fire, accidental, and blamed it practically entirely on the manufacturer of the battery. I do not go to YT to listen to things I already know, to contribute to ones view count. However, he seems to be jumping very far so the blame does not fall on him, the person who modified the circuits, and places blame solely on the maker of the battery.

[youtube]JCaDz_2YcGQ[/youtube]
FROM the youtube description
Description
I teach Macbook component level logic board repair from a common sense, everyman's perspective. I try to make it seem viable, and entertaining.

I also go over business concepts & philosophy that will be important to running & maintaining a sustainable, profitable business.

You can read more about our company here & inquire about service. https://www.rossmanngroup.com

This is the circuit he used that burned. Alot of things he says does not make sense, and are blaming the manufacturer, and not allowing the blame to meet his own poor designing .He says "Hall sensor board" when it is really the entire "controller PWM and inverter bridges" , referring to the BBSHD... Items like that lead me to believe he is kinda " flying by the seat of his pants" when he makes assertion ..... He thinks a SammySung 30Q 18650 is " really high output" {sic} He thinks an ebike battery is " a large high capacity battery" {sic} .. Lol. He thinks he did not " get what I paid for" {sic} when he made stupid modifications with inherently unnecessary complication. He did something that is not condoned, and missed in translation, for any of many reasons. He thinks he knows everything. He just trashes UPP and recommends the EM3EV. I kind of think it is a market campaign.


At least I know, I do not know everything.
 

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Battery fire is a nice vivid consequence of idiotic effort of Louis Rossman.

rg12, what difference do you expect between the two batteries ? There is a safe voltage difference range for connecting the batteries. Just don´t understand why you are still active on such trials.

https://endless-sphere.com/forums/viewtopic.php?f=14&t=104500&p=1526939#p1526939
https://endless-sphere.com/forums/viewtopic.php?f=14&t=103126&p=1508455#p1508455
 
You have to take into account the power dissipation of those diodes: multiply diode voltage drop (usually between 0,5-1V) with current draw from your packs; so you may get somewhere around 5-20W of heat. Unless the diode has a heat sink and adequate air flow to it, I wouldn't recommend.
 
True, heating needs to be taken into consideration.
There are seriously low voltage drop diodes and you can parallell them if needed, just get a LED heatsink that sticks out into the air or use the bike frame as a heatsink. Those problems are solvable :wink:
 
One problem with diodes (and FETs, etc) is that a fairly common failure mode is shorted, both directions. (some resistance, but low). If the safe operation of a device requires the diode to block reverse current flow, and there is no fast-acting fuse present in the path to prevent that in the event of a diode failure....


The diode itself may burn open under enough current flow, once it has failed, but if it was a high-current device in the first place, it might take more than the device it was meant to protect...
 
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