why can't I charge my lithium with a transformer

[Hummina Shadeeba]

I'm still lurking around the forum trying to find the answer to what I thought would be easily answered, and it's not answered.

If the load or voltage contrast between the primary coil and secondary were a lot, there would be a lot of current, just following ohms law, and there could be a lot of current, and I haven't done the math there, but what is it about lithium where it wouldn't be able to sit on a constant voltage from a transformer, a straight power supply, at 4 volts, if it were nicely smoothed?

https://www.google.com/patents/US5659237

 

[kneedeep]

A lithium charger pulls the amps back when it get close to charged to not over charge. From my under standing a Lithium drops voltage once in an overcharged state unlike SLA. If you were using a low amp charger on high AH cells I believe it could work charging at 4v but cut down amps at say 3.6V. But I do not know this for sure and would not try it.

 

[wesnewell]

Transformers use an ac input and put out ac current. To charge a battery, you need to rectify the transformer output into dc voltage. A simple rectifier is 4 diodes.
https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=transformer+rectifier+circuit

 

[amberwolf]

So what's wrong with your other thread about this?

 

[Chalo]

One of the things I think you're failing to appreciate about charging with a transformer is that a charging battery isn't just a load; it's also a voltage source. When the coil isn't energized to a similar voltage as that of the cell, it represents a low resistance load for the cell. There would need to be a power diode on the coil to prevent the battery from discharging into it.

In each diode you'll dissipate about 20% as much charging energy as the amount of charge entering the cell. And you'll need a means of getting that waste heat out without unduly heating the battery.

Between a special transformer, all those diodes, and all that heat management, I don't see what you have to gain that offsets the effort, expense, and inefficiency. Modern BMS does this stuff digitally for good reasons.

 

[Overclocker]

no one charges li-ion w/ a simple transformer PSU i.e. rectified and filtered, because they're not regulated. output voltage fluctuates with AC input. also fluctuates w/ load

that's why DC power supplies have chips in them that monitor the output voltage and perform the necessary corrections to ensure stable DC output

 

[Hummina Shadeeba]

What's coming out of the wall is always going to be the same voltage right? And I just have to smooth it out and then the only obstacle would be making sure not too much current rushed into the cell when it was in its lowest charged state. I'm seeing this maybe overly simply but I haven't heard a good reason for why it won't work
I don't believe I'd need a power diode or something to stop power coming from the cell back into the coil as I think I should be able to get a consistent constant voltage from the wall which will always be higher than the cell. Or maybe I'm wrong but a simple diode wouldn't be hard to add anyway.
I started this thread because it's been a long time and I still haven't gotten a thorough explanation of the obstacles. I still don't think it's impossible.
13 coils on a toroid, one primary and 11 secondaries with the right amount of turns and rectification and smoothing..to simply go straight to a lithium cell? Sure there's more efficient ways to balance like a bms but I just want to find what the obstacles are to doing it this way. Even if this were to transfer very small power it would balance even if I never got near full charge as the lowest cells would get the most current as controlled by ohms law.

https://learn.adafruit.com/power-supplies/transformer-based-ac-slash-dc-converters
http://www.ko4bb.com/e102/e102-4.php

 

[wesnewell]

Where I live wall voltage depends on other loads on the circuit. It is never constant and will vary from 109V to 125V. Put a copy machine on the same circuit and you may see it drop under 100V. You need to regulate the output voltage.

 

[Hummina Shadeeba]

Ok. I'm believing that while this is possibly doable, and the load could be assumed to be a certain amount based on the cell voltage and resistance, the complexity is building and I'm now wanting to make a much simpler balanced similar to a battery medic like thing for 10$. I have a bunch of these and they work except they can only discharge a very low power from the cells and it takes forever

http://www.thinkrc.com/battery-medic-balancer-and-discharger-p-1723.html


So extreme mind change. I think it'd be much easier to make something like this. Safer for sure. Any direction to look for how it's done? So point is now to still make a simple balancer while all cells are connected in series

 

[amberwolf]

So it took you THREE THREADS for the same thing to decide to listen to what people were telling you?

Do you just like trolling by dragging out replies from people?

 

[spinningmagnets]

Hummina Shadeeba, it sounds like you are going to try this, in spite of all the warnings you have been given. I also would like to state that this is a bad idea. If you are asking "what will happen if I try this?" then...I don't know. All I'm asking is that...if you do try to do this very dangerous thing, please put the battery out in the middle of some concrete, so if it catches on fire, there will be no damage to your home or anyone elses.

 

[Hummina Shadeeba]

After going through the construction and obstacles with my friend who went to MIT it's not impossible and I might still make it as he likes the idea of making it. The complications are now known and it's not impossible. If u think it's too dangerous to do.. toughen up.

 

[Inwo]

You are making this way to complex. All you need to charge battery is a transformer and rectifier. Transformer, dumb chargers, are common and useful.
Why all the questions and doubts? Just pick one up at nearest retailer and try it.
In theory, transformer is optional. Smoothing not needed.

However:
It will not limit voltage.
Will not limit current.
Most surely will not balance cells.
Without transformer there is extreme shock risk.

Anyone who asks a question like this does not have the skills to playing with this new "electricity" thing.
My apologies if you are under 8 yo.

 

[MrDude_1]

What's coming out of the wall is always going to be the same voltage right?

nope. your AC voltage will change throughout the day... and place to place will change too. its always in a range though.. for example, in the USA you will get between 107 and 121v ac from any average outlet... my garage reads 117 most of the summer, but 120 all winter because everyone runs AC in the summer...


so your input changes and you will need to compensate for it.
also a lithium battery is "low resistance" so you will need to limit current or it will seem like a dead short... (or set the voltage to just above the current battery voltage, then slowly raise it.

you want to do this with dumb 1800s tech? you need a variac (a variable transformer you can turn up and down with a knob) along with your stepdown and diodes... all together you can build a dangerous but technically working charger.... but it would be silly to use it for anything other than a science experiment.

 

[MrDude_1]

heres a fun dumb idea.

https://www.youtube.com/watch?v=P9UjxG8sN1c

[youtube]P9UjxG8sN1c[/youtube]

[moderator edit to fix link]

 

[Hummina Shadeeba]

Thanks for the info. I can't see that video now not this phone but sounds good and scary as the best electronic stuff is. I think I got about ten people angrily telling me I'm going to kill myself and don't know what I'm doing.

So as to avoid starting a new thread that's somewhat related and it seems some here know what the hell they're doing, could you please point me in the direction of how to build a circuit that can balance while all the cells are already in series such as this one:
http://www.ebay.com/itm/like/301291083200?lpid=82&chn=ps&ul_ref=http%253A%252F%252Frover.ebay.com%252Frover%252F1%252F711-117182-37290-0%252F2%253Fmtid%253D1588%2526kwid%253D1%2526crlp%253D53601919689_324272%2526itemid%253D301291083200%2526targetid%253D186358904649%2526rpc%253D0.08%2526rpc_upld_id%253D100933%2526device%253Dm%2526mpre%253Dhttp%25253A%25252F%25252Fwww.ebay.com%25252Fulk%25252Fitm%25252Flike%25252F301291083200%25253Flpid%25253D82%252526chn%25253Dps%2526adtype%253Dpla%2526googleloc%253D9031952%2526poi%253D%2526campaignid%253D239125209%2526adgroupid%253D14978428809%2526rlsatarget%253Dpla-186358904649%2526gclid%253DCjwKEAiAlNbEBRCv9uy4j4SWrgwSJAB5MqJFGMN1uFKjdnt_LQ99l61H-jIL374B0GuEh8yKnVeXZRoCBzTw_wcB%2526srcrot%253D711-117182-37290-0%2526rvr_id%253D1163504953152&ul_noapp=true

10$ balancer. I wouldn't need the screen just something able to do the job much faster than this. I have 4 different versions of this including the one with the bulb (which wouldn't work w my stuff) and all are very slow.

 

[Inwo]

Simple as you could find. Up to 2 amp rate with heatsink or fan.

https://endless-sphere.com/forums/viewtopic.php?f=31&t=85837

http://www.ebay.com/itm/232199988254?ssPageName=STRK:MESELX:IT&_trksid=p3984.m1555.l2649

 

[Hummina Shadeeba]

thank you very much!