battery voltage vs AC voltage

[cerewa]

All of the battery chargers I have seen use a step-down voltage converter of some sort in order to efficiently charge the battery. I don't think it would save all that much, but I'm sure you could save a little bit of electricity by dispensing with the converter entirely and just using diodes to turn AC power to DC directly. (http://en.wikipedia.org/wiki/Diode_bridge). What I'm not sure about is what else would go in to a good transformer-less charger. For 120VAC power, I think the diodes would give you at least 115VDC power out. Add some kind of current limiter, and I suppose you could charge a large series string directly off the 115VDC power. (Idunno, maybe it would ideally be a 110V pack? or 100V?)

I'm curious if any of you have thought about doing this, or know what kind of components one would have to buy to make it work. (obviously a high voltage controller would be necessary to USE the battery.)

 

[TylerDurden]

ES member monster was charging off mains... I can't find the thread about it.

 

[frodus]

first problem: By doing this, you are taking the risk of fire/electrocution mainly because the transformer isolates the AC and DC, by taking that away, you take away the isolation. You could potentially create a dangerous device by doing so.

Next problem: 120VAC is not 120VAC peak, its 170VAC peak to peak. This would mean, you'd have 170VDC once you go through the bridge rectifier. You'll also want to put caps on the output of the bridge, as there will still be a waveform, and you want to smooth this out. Still, you'd have 170VDC.


Also, there is no control, its just AC, through Diode to the pack...

 

[Knuckles]

You are describing the classic "bad boy" charger. Many many posts on this. Search 'bad boy charger'.

 

[frodus]

You are describing the classic "bad boy" charger. Many many posts on this. Search 'bad boy charger'.

that still uses a transformer.....

 

[Knuckles]

True that

 

[safe]

I mentioned the idea in the "bad boy" charger thread. Just go without the transformer and even the smoothing... no need to smooth (someone else pointed this out to me) anything because the battery acts like a capacitor anyway. (you need to design your pack to fit the voltage rather than the other way around)

You still need all the cell monitoring to do charging though otherwise if this was left on for too long it would burn up your battery.

 

[cerewa]

If chargers were smaller, lighter, and created less heat when in use, you could attach your charger to your battery like it's part of your BMS, and just plug your battery in to the wall whenever you feel like. Less fooling around with separate parts. Easier to charge away from home, at a cafe, at a restaurant, whatever.

One of the things I would like to see someone do is a 500+ mile trip on an e-bike with few accomodations required for the fact that it's not a gas vehicle. Combine a charger that is very light and small and attached to your battery, and a battery that can handle high charging current, and you'd be set. (Although you'd still have to make sure you don't blow circuit breakers at your favorite restaurants/other charging places away from home.)