Downgrade pack voltage

[katou]

I have the feeling that this is a really simple thing to do, but I don't know how to do it. I also notice that no one else has done it, so maybe it's not so simple.

I would like to have a high voltage pack (say 70v) but only output 50v to my Castle Creations HV 110 ESC.

How can I do that?

This question is important to me for other reasons as well. I would like to make larger battery packs for things around the house (phone, cordless drill, etc) but I know I won't be so lucky as to accidentally have the cell voltage match the voltage required by the device.

Thanks!

Katou

 

[fechter]

In general, for smaller loads, you can use a buck regulator or dc-dc converter to drop the voltage.
For a heavy load like a 110HV, the size of the regulator becomes an issue, along with heat generation.
In a case like that, it may be easier to tap into the right number of cells in the battery so the voltage is what you want.

In other words, a voltage reducer that handles 100A is going to be humongous and expensive.

If you have 70v, many switching power supplies made for 120vac will work directly off 70dc.

 

[amberwolf]

It would be a lot more efficient just to use a controller that can handle the full pack voltage, and let *it* do the downconversion, simply by using less than full throttle. Perhaps by using a low/med/hi switch that can tell the controller to not use true full throttle even when you gun it (like my Fusin has).

Less stuff on the bike, less stuff to fail, less wasted power.


That aside, if all you have right now is a lower-voltage controller, and you want to add Wh to your pack by increasing it's voltage (which is what I am after on DGAmII) then modding the controller (if possible) is probably a better option than "bucking" the pack voltage.

If you *had* to buck the pack voltage down, though, using some type of SMPS would be a more efficient way than any other I can think of offhand, assuming you want to always run from the full pack to keep cells balanced relative to each other.

 

[katou]

SMPS?

I get the buck circuit thing, I googled it and found an explanation on Wikipedia.

How would I design one? Lets say I want to make a battery for a cordless phone that needs 4.6v
One cell 3.7v cell is too little, two is too much.

I would love the mod the controller Amberwolf, or perhaps I should say that I would love to have the know-how to do so.

I am interested in the pack level voltage because of charger issues.

I will explain a bit more:

I want to use a SLA charger that puts out 48v, but the float point of the charger is higher than 50v, approx 57v if I remember Justin at ebikes.ca correctly. That means that a hot pack will blow my speed controller.

So, I want to charge using a charger that is rated at near the pack voltage, but have some way to bring the pack voltage down to ensure that the controller is safe.

The highpower chargers that Andy sells may be the way out of this, but I'd still like to understand how to do it for the smaller projects I have around.


Katou

 

[amberwolf]

SMPS?

Switch Mode Power Supply. Basically nearly all the chargers, ac adapters, wallwarts, etc. made today use this instead of just a large transformer, rectifier, and caps, because it's a lot more efficient for the weight and size--enough to justify the increased cost. Your computer power supplies are SMPS, too.

How would I design one? Lets say I want to make a battery for a cordless phone that needs 4.6v
One cell 3.7v cell is too little, two is too much.

Well, most likely you could start at the Roman Black website, and work with the two-transistor SMPS circuits he has there. They're pretty simple, and very easy to build from what I can see. You'd just need to figure out what values to use to regulate at 4.6V output (one of them goes from 12V to 5V, so you could start with that and figure out what it takes to bring the input down to however many cells you want to use, and the input down to 4.6 instead fo 5).

Alternately, you could use a boost circuit to go from 3.7 to 4.6, since likely the current demands of the phone are quite low and you'd be able to make the new "pack" for it smaller with only one cell.

It is a bit odd that it's 4.6V, though. None of the cells I can think of would add up to that voltage, other than plain old primary cells like 3x AA or something, which comes up to 4.5V, and would not be rechargeable.

I would love the mod the controller Amberwolf, or perhaps I should say that I would love to have the know-how to do so.

What kind of controller? There are instructions for a number of them around ES, and I have been digging into the threads about them so that I can learn now I might be able to do it for my 36V Fusin controller. (I want to do it simply because I can then use a 24V and a 36V NiMH pack I have, in series, to use all that extra Wh I'd get, since I cannot parallel them due to different voltages.)

Seems like a lot of controllers don't take much to mod them for higher voltage. The caps, sometimes the FETs, and some resistors for a voltage divider on the controller's internal power supply--those are the usual things. Sometimes other stuff.

 

[katou]

I made up the voltage for the phone! I don't know what the voltage is exactly - I just picked that voltage for purposes of discussion.

I am using one of the High Voltage series ESC's from Castle Creations. All of them go up to 50v max. I wouldn't even begin to know how to mod that tiny little thing.

Thanks for the explanation, that helps a lot. I'll check out the Roman Black website, I know that one of my nicad Ryobi batteries for my drill is dying, so I need the info to determine which way to go on remedying the situation.

Katou

 

[amberwolf]

I made up the voltage for the phone! I don't know what the voltage is exactly - I just picked that voltage for purposes of discussion.

Ah...you know it's easier to help with actual numbers.

If the phone doesn't have any marked voltage on it, just list the number of cells in it's little pack and which type--that'll show what it takes. My guess is that it uses NiMH and that it is two or three cells, as all but one of the ones I've fixed/had/opened/etc. has been so, and almost all of those were 3 cells.

If so, it is probably 3.6v nominal already, and you could just plop in a single cell, as long as you charge it externally rather than letting it recharge in the phone (since NiMH is a totally different charge method than Li). Otherwise, it's probably 2.4v nominal, and you would be best with a buck regulator of some kind.

I am using one of the High Voltage series ESC's from Castle Creations. All of them go up to 50v max. I wouldn't even begin to know how to mod that tiny little thing.

Ah...well, I don't know if anyone has modded one before or not. I suspect that they are a lot more difficult to physically modify due to SMT parts than the usual ebike controllers would be. If yours has SMT MOSFETs, those would likely be hard to replace (and almost certainly would need to do so for a large voltage change, but possibly not for the change you are making, depends on their specs). The capacitors probably need to be changed, but maybe not, and then there is whatever internal low-voltage regulator it uses for powering itself off the pack. Probably is relatively simple to determine what needs to be modded, but hard to actually do without risk of PCB damage, if you have to change SMT FETs.

Thanks for the explanation, that helps a lot. I'll check out the Roman Black website, I know that one of my nicad Ryobi batteries for my drill is dying, so I need the info to determine which way to go on remedying the situation.

The drill is probably 9.6 or 14.4v. If the former you may need to boost or buck a pack. The latter though would be 14.8v nominal for four cells, and it would probably be ok with that, though you would want to charge the pack outside the drill.

 

[katou]

So, anyone know how to build this "bucking circuit" thingy?

Katou

 

[amberwolf]

That's why I suggested the Roman Black site, as he has them there with explanations of operation and such. Since you'll need to customize yours for the input and output voltages, you'll have to calculate component values for the circuits you choose to use. An SMPS is more efficient than a "dumb" linear buck regulator (like the LM317 and similar), since it doesn't just dissipate all the unused power as heat.

His is probably the easiest DIY SMPS I know of to work out for low-power applications, and it can be adapted for higher power stuff by using higher current/voltage capable parts, larger wires, etc.

What specific questions did you have about building one?

 

[katou]

I checked out the Roman Black website, but I'm not seeing anything on there that is adjustable? I saw his Pic as a SMPS but it seemed to have only 5v, 3.3v, and 13v I think?

Did I miss it?

Katou

 

[amberwolf]

Not "adjustable" in that there's no adjustments for a wide range within any of the individual pre-calculated converters he has there, but the design can be adapted to a wide range of voltage conversions:
http://www.romanblack.com/smps/smps.htm
You could make any of them adjustable to a degree, using pots for some of the resistor values, at the least until you determine exactly what value to use in a particular component for your design.

I thought I remembered better explanations for which specific components did what, but they may be on another page. There are some explanations down at the bottom regarding the use you want to put it to, of a high-voltage input, and which components need to change value in what direction. You'd probably have to experiment with specific component values in one of the other designs, like this one:
http://www.romanblack.com/smps/a03.htm
based on those component change "hints"

Also, you could probably contact him and ask about it, he might be willing to help directly, or at least give a better explanation of why each component is a particular value.

I had been planning to use a few different RB designs, modified for my voltage needs, on CrazyBike2 to power things like the 12V lighting system, the PDA with VeloAce, the CFL lighting system, etc., but I have not gotten around to it yet. Once I do, I'll make a thread for it, but I suspect you're going to have yours done long before then, given the progress I'm not making on things these days.