Emergency "Bad Boy" ultra Compact charger

[tno]

how about running 2 parallel packs at half of 165v and then charge in series

 

[monster]

just build your pack to suit the mains voltage. you guys with 110v mains have got it easy (and safe). us in england have to run 240v packs with series/parallel switch to prevent frying the controller.

a light bulb will limit the current
http://cgi.ebay.co.uk/Hardman-500w-...VQQcmdZViewItemQQ_trksidZp1638Q2em118Q2el1247

 

[safe]

just build your pack to suit the mains voltage.

That's what I was saying. If everyone built their packs to be the same voltage as the standard voltage from a plug then you would be able to charge directly. Seems there's some debate about exactly what that voltage is. Is it 104volts? 165volts? (based on the peaks) I never got a good answer on that... :?

 

[lazarus2405]

Is it 104volts? 165volts? (based on the peaks) I never got a good answer on that... :?

Well the AC voltage is 115v. Using a multimeter, I got a value of 105v out of the bridge diode. However, just because it is rectified doesn't make it really pure DC.

My multimeter was trying to measure the unsmoothed last graph, and came up with 105. A capacitor with no load will be charged up to that peak, at 165v. So, we're looking at getting a 165v out of an outlet.

So, I don't understand the relationship between charging voltage and battery voltage. If I plug a current-limited 165v power supply to my 105v discharged pack, what happens? It's a resistive load, and it's a 60v potential, so it will draw current according to Ohm's Law up to as much as the current limit will allow.

And all that voltage doesn't pose any problem to the battery? And in that setup where do you place the leads to monitor the battery voltage while charging (and not the supply voltage)?

So, as I understand it, this is what we want:

View attachment badboy.JPG

Will that do? I can't decide whether the pi filter should be before or after the bridge rectifier. If it is before, it doesn't smooth the rectifier output, but if it is after it exposes the rectifier to current surges. :?

And for it to output 10a, how do all the components need to be built? Especially the inductor and capacitors?

 

[Frank]

I don't think the capacitors on the output side of the bridge do anything - the batteries act as a large capacitor. According to EV guru Lee Hart, the inductor goes in series with one of the AC input wires and the capacitor goes directly across the AC line, before the inductor. (I'm building a bad-boy for my pickup conversion and am facing the same issues - 120 VDC pack.)

 

[safe]

I don't think the capacitors on the output side of the bridge do anything - the batteries act as a large capacitor.

Wow... that's a great realization.

Yeah, within limits I suspect you could just pass the unsmoothed voltage into the battery and the battery itself could smooth it out. In fact, if I remember correctly with SLA, it tends to prefer being "shaken" a little... at least on discharge. I'd be curious if all chemistries like this "shaking" going on. (somehow I suspect that some will not like it so much)

Do you know if Lee Hart was talking about SLA's alone or was he saying this is a good idea with other chemistries?

My big concern would be how far above the normal DC voltage you should go with the spikes because at some point all that excessive spiking is going to do damage. I'd guess you want to take an average of the AC-to-DC chopped pulsating voltage as your equivalent max charge voltage. On average if the voltage is equal to the standard maximum charge voltage then it should be fine.

 

[shredator]

The biggest questions in my mind are:

1. Can the batteries handle the current peaks of an unfiltered rectifier or triac without shortening their life? If no, then we need filtering. I think that the size/weight of an inductor needed to make a pi filter might limit the portability of the charger. I think that a resistor would be better and cheaper.

and:
2.Can a bms handle the rf hash from the rectifier or triac? I really have no idea what types of components are used in bms'es. maybe this is a dumb question.

One more question about filtering:

An triac based light dimmer is really a switch that is either on or off. It just switches at 120hz. By reducing the duty cycle, the average current will be reduced, but the peak current will be a function of the peak voltage and the circuit (mostly battery) resistance.

doesnt a switch-mode power supply work sort of the same way? how do switch mode power supplies limit peak current? do they use pi filtering? I have built tons of 'linear' power supplies for guitar amps that all used pi filters, but I only vaugely understand how switch mode power supplies work. Is there some better way to filter?

 

[monster]

i've been using my "bad boy" charger as my main charger for months now. so in my mind its proved.

 

[lazarus2405]

i've been using my "bad boy" charger as my main charger for months now. so in my mind its proved.

Exactly how is yours wired? Please share everything!

 

[monster]

right lets revive this thread!

i am only now starting to understand the theory behind this idea and i think others hear were also confused. i didn't really know what a triac did before (because i don't understand electronics speak ) but now i know.

a triac is basicly just a fast acting switch that can switch on and off the power -chopping it to reduce its average power. this is then smoothed somehow and the result is a reduced voltage which we can use to efficiently charge a battery. we can select any voltage (lower than mains) by using the right ratio of on's to off's (the duty cycle). more off's when smoothed will give a lower voltage output. this is called a buck converter.

this is different to my circuit where i limited current with a light bulb which wasted the excess power. and it is different to matching the battery voltage to mains.

however it seams that lots of people have different objectives here because of different battery voltages and different mains voltages. (some want voltage up)


i have two ideas
-if we can switch it with the right duty cycle, rectify it and smooth it out then we will have a decent charger. there will be no super high peaks -they will be smoothed out. this will reduce mains voltage down to pack voltage creating a very efficient charger.

if smoothing is difficult, another option is available. clip the waveform accurately so that the high peaks are chopped and only the voltage we want remains. this idea could be combined with the light bulb current limit idea to reduce the voltage with out smoothing (or with less smoothing). this would involve some resistive losses but it could be a lot less than the simple light bulb charger because of the lower voltage.

so the issue is how can we switch it?
and
how can we smooth it?


we can follow many of the circuits used for the DIY dimer switch except we may still need a light bulb in series with the battery because the battery resistance is so low it would fry the dimmer.
http://www.electro-tech-online.com/electronic-projects-design-ideas-reviews/15790-light-dimmer.html

 

[monster]

how about this?

 

[safe]

I've been closely monitoring my 20 cell NiCad tube sets and they all charge up to about 28 volts before they start to get full.

When you get up to 30 volts it's a potential catastrophy and the cells overheat if the current is allowed to flow, but down at 28 volts there's no problem.

If you can get about an 80% charge with a constant voltage charger then why not rapid charge up to 80% and then just use that or switch to top off chargers after that?

Basically the idea is to never fill up the cells completely (unless you want to go for full range in which case you revert back to individual chargers) but you charge ALL THE SETS in parallel with a single high amp charger.

Since you never get near being full (20% capacity for safety) you don't need to worry about cutoff's. (since you are nowhere near the cutoff)

This is "quick and dirty" charging but without the risk if you limit the voltage to BELOW full charge voltage.

Am I correct here?

NiCads have a very high self discharge rate and I've found that their self discharge amounts to about 15%-20% of the capacity overnight anyway. No matter what I do overnight I end up needing to "top off" to get that last 20%. (it takes about 15 minutes to "top off")

See my point here?

 

[dnmun]

nicads are 100% charged at 1.41V, with increased charge, the voltage will drop and most smart chargers look for this drop in voltage as it exceeds full charge. allowing the nicad to charge beyond this results in gas formation inside and the pressure will blow out the vents and cause the cell to dry out, leading to early failure. mine shuts off at 56.4V or so for 40 cells. if you are over that, you are ruining the cells.

 

[safe]

nicads are 100% charged at 1.41V, with increased charge, the voltage will drop...

1.41V * 20 = 28.2V

...I was thinking that if you kept the voltage a little lower than 28 volts (so 1.40V or less) and watched the current flow that you might see the current reduce, but maybe that's the wrong chemistry. SLA's tend to resist current when they are full, but I guess NiCads don't resist the current, but show their full status with a lowered voltage and increasing heat.

You could still time the charge, so maybe you turn on the voltage to 28 volts and allow 30 amps (for a 20Ah setup) for about a half hour and watch it, but it does get scary to do this sort of thing.

Does current reduce after a NiCad becomes full?

Probably not huh?

With the NiCads you probably are stuck with individual chargers because you can't parallel them for safety reasons if the full string is able to suck up current even when it shouldn't.

(I think I forgot about the "unrestrained current" problem)

 

[NeilP]

To drag up this old thread again..there was mention of a bad boy charger..which I can not find now, that used a capacitor (like large motor start ) as current limit before the Bridge rectifier.

Capacitance value determines output current.

Now, please, no one mention adding a light bulb or a hair dryer..that immediately, means the 'charger' is no longer portable or rugged.

Now as I remember reading, it ' self regulates ' the output voltage..in that it just allows the current to flow, limited by the capacitor and its 50HZ charge/discharge cycle, and the output voltage rises as the pack charges...OK, you definitely CANNOT leave this un monitored as it will take the pack to a 1.41x the mains voltage.

I am guessing a smoothing cap on the output would not work as it will hold the output at max peak to peak voltage.

So leaving out all the LiPo warning , safety issues, explosions, dramatics etc, advice to add a light bulb or hairdryer. will that basic circuit, instantly go over voltage on the pack and explode it instantly , or will pack voltage slowly rise as it charges. Yes no PFC, very in efficient but does that circuit as shown actually work correctly if monitored for a few minutes or two


It is just something to plug into the pack, and sit and watch for 2 or 3 minutes or less, as a quick boost charge.

 

[Doctorbass]

Hey Neil,

you waked up this old thread that is like 5 years old now

I agree with you, i would never charge lipo with that kind of unstable charger. or.. would charge to 4.0 or 4.1V/cell MAX and keep an eye on the voltage during all the charging process as well !

Doc

 

[Tommy L]

Hey Neil,

you waked up this old thread that is like 5 years old now

I agree with you, i would never charge lipo with that kind of unstable charger. or.. would charge to 4.0 or 4.1V/cell MAX and keep an eye on the voltage during all the charging process as well !

Doc

So what are you using Doc?


Tommy L sends....

 

[NeilP]

Hey Neil,

you waked up this old thread that is like 5 years old now

yes, well there was another thread, similar, but jsut cant't find it..I am sure it has the naswer I am looking for..but cant find the thread

I agree with you, i would never charge lipo with that kind of unstable charger. or.. would charge to 4.0 or 4.1V/cell MAX and keep an eye on the voltage during all the charging process as well !

Doc

No plans to use it as an everyday charger that is for sure, just want something to carry to fire a few Ah in to the pack while on the road. T- in to the power leads, keep the controller and CA powered on and monitor the voltage.


But will it work? that is the question..does the output voltage actually 'stay' at pack voltage...slowlly rising to max voltage ( 240 x 1.41= 380v) as the pack charges..or does it instantly put 380 volts across the pack?

I suppose I can just try it with some old packs I have and see what happens......video to follow maybe I'll let one go all the way

 

[Doctorbass]

Hey Neil,

you waked up this old thread that is like 5 years old now

yes, well there was another thread, similar, but jsut cant't find it..I am sure it has the naswer I am looking for..but cant find the thread

I agree with you, i would never charge lipo with that kind of unstable charger. or.. would charge to 4.0 or 4.1V/cell MAX and keep an eye on the voltage during all the charging process as well !

Doc

No plans to use it as an everyday charger that is for sure, just want something to carry to fire a few Ah in to the pack while on the road. T- in to the power leads, keep the controller and CA powered on and monitor the voltage.


But will it work? that is the question..does the output voltage actually 'stay' at pack voltage...slowlly rising to max voltage ( 240 x 1.41= 380v) as the pack charges..or does it instantly put 380 volts across the pack?

I suppose I can just try it with some old packs I have and see what happens......video to follow maybe I'll let one go all the way

Neil, the other thread you are looking for is named like: Poor man,s charger or something like that... :wink:

Tommy, no i am still not using any bad boy charger. but this doesn't mean i will give a not try... almost fo rmy zero motorcycle! :wink:

Doc

 

[fivari]

Here is the topic. It works, but there is this safety issue.

 

[NeilP]

Ah yes, that was the one, but reading it has to wait till I get home. Just arrived in England, and checked in to hotel, 2300 hrs , and only phone to read it on.
Thanks

 

[heathyoung]

Or alternativly, you can have a look at my thread on using capacitors as voltage dividers and you can have any output voltage you want, and current linited.

 

[fechter]

It will act like a constant current source, so the voltage output will match the pack.
There are a few other threads on this idea. Here's one: http://endless-sphere.com/forums/viewtopic.php?f=14&t=19658&start=50

 

[NeilP]

It will act like a constant current source, so the voltage output will match the pack.
There are a few other threads on this idea. Here's one: http://endless-sphere.com/forums/viewtopic.php?f=14&t=19658&start=50

Thanks for answering the exact question, that was my understanding, just wanted to check, as I could not get my head around it.

Will search for your thread too heathyoung, but buy the sound of that, it has more than one capacitor, therefore possibly a bigger package required.

 

[NeilP]

Or alternativly, you can have a look at my thread on using capacitors as voltage dividers and you can have any output voltage you want, and current linited.

is this the thread?

http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=48976&p=722466&hilit=+capacitive+divider#p722466

I had glanced at it before, but no schematic so I did not explore any further. Some sort of schematic to show how it is done would be appreciated if you had the time
Cheers