The old 37V to 15V conversion question again

Reid Welch

Reid Welch

1 MW
Joined
Nov 18, 2006
Messages
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Location
Miami, Florida
I recall very little of a long-ago discussion at the defunct panel.

My want then was direct DC to DC conversion of non-standard voltages,
about a four amp output.

I hope I can be steered by fechter the fantastic or other big brawny brains here,

the EV Tech pack will be at 42 to ca. 33V across its discharge range.
I'd like to run my 12V nominal 20W halogen headlamp at a regulated 15.5V --for the white color, brilliance and lumen efficiency.

I can use the same regulated voltage to run my motor's hair drier force cooling blower.

I did these things before now with a 14.4 NiMh water bottle battery.

It'd be nice to lose that time-limiting water bottle, and work directly from the bike's pack.

Efficiency isn't a concern.
Reasonably decent regulation is the want,
so the output should remain within a volt or of target regardless of the load (light plus blower, or light sans blower, or no substantial load at all.

I can't use 12V output===the headlight is too weak and yellow at 12V.
It lasts just fine for me at 15.5V

Is there a turnkey solution?

Can I pay anyone here to make for me a 4A converter?

Thanks for advice,


Reid

_____________
edit: post-posting I thought to Google.

I find Powerstream, and have sent off a note of inquiry.

Maybe they have an off the shelf unit that can be adapted to do the job.

http://www.powerstream.com/dcdc.htm
 
Hi Reid
Lets look at this site:
http://www.elektroda.pl/rtvforum/topic577776-120.html

there is adjustable converter from 60V to 2-24V @20A, so it should work fine for 37V @input.
(To get access to attachments(schematics etc.) you need to register.)

You can get it for relatively small money i'm sure.

Other way is 10 buks cheap kit for step-up 12V->15.5V @6A.

I hope this info will be usefull.

Piotr
 
Hi Reid

Contact Bob Mcree he had some nice DC-DC converters I am sure he would be happy to pass on.

Cheers

Knoxie
 
I found this forum accidentally when i was searching for LiFePO4 cells information.
I have two bikes (none of electric ) for now.
I'm riding by bike for health improoving ( over 2000 km last - and first - season ).

I'm interested in very efficient motor for assistance. I live in semi hilly area so i dont care for speed but mostly for tork and efficiency at low speed.
I need assistance for limited time frame only. Maybe 40% max. time my biking, so the one of most important parameters for me is the idle power.
When i will use assistance for 20% of time for example i have to add 4 times idle power to input power to get real efficiency in such case.
At low cycling speed light weight is also important -low rolling resistance.
So i'm looking for the best (cheap and powerfull) solution for daily commuting.

I'm a member polish hobbyist's (EV) forum:
http://forum.arbiter.pl
but nobody there have the same target like me so far.
Most want speed and power, so i'm very impressed you build up such comprehensive and very active forum at such short time ( few months).

Cheers
 
This is the best one I've seen around lately:
http://www.thunderstruck-ev.com/dcdc.htm

DC-dc.jpg


There's some smaller ones here:
http://www.salvagetech.com/products.asp?cid=42
but most of these don't span the proper voltage range and the biggest ones are 20w.
 
fechter said:
This is the best one I've seen around lately:
http://www.thunderstruck-ev.com/dcdc.htm

DC-dc.jpg
Click to expand...

The first one is not adjustable i'm afraid.

Maybe the better option is looking for converter which could be able to work at much more power level for regen braking purposes also ?
It could work with supercaps, or for converter which could work at both directions ?
 
How regulated does it need to be? And how efficent?
A simple resistive voltage devider bridge could give you any voltage you want, if it didn't need to stay latched at 15.5. Its just 2 resistors.

Or you could use a 24V regulated DC-DC converter and then use a resistive voltage devider to give you any voltage you want with a minimum of parts,
 
obviously you cannot use a resistive voltage divider to power a light bulb without throwing away lots of power. you could use a 3 terminal linear regulator like the LM318 but it would waste just as much power and 50w of heat is a lot to deal with and a lot of battery to waste.

the best solution is a switching voltage regulator. i have used the National LM2576HV which is a 3A device, and it is working fine to power the 30W HID lamp on my bike from my 48v battery. You can use these up to 60v in and adjust the output from 3-55v with a resistor pair. the regulation is better than 0.1% and they will do 4A with some extra heat sinking.

these "simple switcher" series parts from National make it possible to build a complete power supply for about $10, from the 5 pin part, a coil, a couple of caps, and a couple of resistors. they are very tolerant of part selection and layout, and work fine just wired together freehand and potted or glued in place. you do need to heat sink the regulator itself with a couple of square inches of surface area if using more than 2A. An aluminum case smaller than a cigarette pack will house the circuit and act as a suitable heat sink.

Rick K has some built for sale, but he has been hospitalized recently and i have no idea about the availability. the ones i have in quantity will accept up to 85v input, but the output is fixed at +/- 12v and they only supply 1.25A so they are good for powering a 13W HID but not your incandescent.

i would normally offer to build one, but we just bought a new house in oregon and will be moving over the next month or two, so i am not taking on any new projects. if you can solder you can build one from the datasheet on National's website.[/img]
 

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i would normally offer to build one, but we just bought a new house in oregon
Click to expand...

Oh no, yet another transient californian moves here to oregon! (californians are notorious for wrecking there vehicles on the wet roads up here ....)
A webfoot welcome anyway....:D
Drive safely and don't run over the guy with the duct-taped ebike. :D
 
i don't drive a car, so no worries there, and the area we are moving to has the same 20" a year rain we are used to here, so it should not be a problem.

i have watched real estate prices rise by 2000% here in the last 30 years, and we just cannot have the kind of home we want here with room for horses and dogs and chickens any longer, so we are moving northward.

i was reading the oregon ebike law, and i noticed a difference in that it says that a person riding an ebike does not need a license, but "must be eligible" for a license. any idea what that means? is it intended to keep people with suspended licenses from operating an ebike?

i am wondering because i cannot get a driver's license for medical reasons, and i hope this will not be an issue in oregon operating my ebike.

-bob
 
i was reading the oregon ebike law, and i noticed a difference in that it says that a person riding an ebike does not need a license, but "must be eligible" for a license. any idea what that means? is it intended to keep people with suspended licenses from operating an ebike?
Click to expand...

By the grace of some higher power, I'm no lawyer, but it sounds to me like the intent is both to keep people with suspended licenses from riding ebikes, as well as anybody the State considers medically unfit to drive a car. I've not found any exceptions for cases like yours'.

http://www.oregon.gov/ODOT/DMV/vehicle/pocketbike_factsheet.shtml
"Although a driver license is not required for motor-assisted scooters, electric assisted bicycles and personal mobility devices, riders must be at least 16 years old (ORS 807.020 and 814.512) and be eligible for driving privileges. It is also possible for a person whose driving privileges are suspended or revoked to be charged with operating any motorized vehicle while suspended/revoked - including a motor-assisted scooter - on public roads.

Driving any motor vehicle on a public road while suspended is a Class A violation with a maximum fine of $720.

Operation by a rider under 16 years of age is a Class D traffic violation with a maximum fine of $90.

A parent or legal guardian of a child younger than 16 years old who authorizes or knowingly allows a child to operate a motor-assisted scooter may be subject to a traffic citation and fine (ORS 814.536), as well.

Riders must follow Oregon traffic laws and any laws that apply specifically to these vehicles, such as wearing a helmet.

A driver license or restricted license is required for anyone to operate a moped (ORS 807.031). Violation of this law is a Class B traffic violation with a maximum fine of $360."

"An electric assisted bicycle:

* is designed to be operated on the ground on wheels;
* has a seat or saddle for use of the rider;
* is designed to travel with not more than three wheels in contact with the ground;
* has both fully operative pedals for human propulsion and an electric motor; and
* is equipped with an electric motor that has a power output of not more than 1,000 watts and is incapable of propelling the vehicle at a speed of greater than 20 miles per hour on level ground.

(ORS 801.258)"
 
thanks, that's pretty much the same as i read into it. i don't really need a driver's license, so i expect that if i just get my doc to say that i could have one if i wanted to that would be enough to satisfy them. i'll figure out whatever i need to do.

this is a pretty strict additional requirement that would appear to make oregon much less ebike friendly than california to people with some medical problems that might make them incapable of safely operating a car but still capable of operating an ebike.
 
bobmcree said:
thanks, that's pretty much the same as i read into it. i don't really need a driver's license, so i expect that if i just get my doc to say that i could have one if i wanted to that would be enough to satisfy them. i'll figure out whatever i need to do.

this is a pretty strict additional requirement that would appear to make oregon much less ebike friendly than california to people with some medical problems that might make them incapable of safely operating a car but still capable of operating an ebike.
Click to expand...

I agree, it's a stupid provision. Although unlikely this unreasonably biased restriction will pose you problems, I find it preferable to operate in accordance with the law rather than constantly looking over my shoulder. But since politicians are beholden more to corporations and the majority voting blocks, what else can a person do when the law is clearly written or applied unfairly to you, short of paying a lobbyist, or making a lonely march on the capitol?
 
those in prison are not eligible.
can't vote either.
stay out of prison guys!

just a guess, who know what they mean? maybe if u don't have a pulse?
perhaps an illegal alien?
space alien?
suffer from incurable insanity?
Totally blind?
 
just a guess, who know what they mean? maybe if u don't have a pulse?
perhaps an illegal alien?
space alien?
suffer from incurable insanity?
Totally blind?

the problem with arbitrary conditions like "eligible for a license" is that it is open to interpretation. it might be construed by one person as anyone over 16 and another as being able to afford insurance on a median price vehicle, which would eliminate many drivers.

it might be construed by another as medical capacity, but then who decides if i am sane or not for not wanting to use fossil fuels? maybe i am sane enough to drive an ebike but not a 1000 horsepower racecar?

my decision to let my license lapse is partly a matter of social protest, so i will have to consult someone who knows more about the law than i do about the minimum i can do to comply. i will do what i need to show i could get a license if i wanted to, without actually getting one unless i must. i am content to ride my bike everywhere and when i need to travel by car i let my wife do it.

-bob
 
Bob, many thanks for setting me up to either build or purchase a switching voltage regulator.
Greatly appreciate your guidance here.

Say, how do I contact Ray K? --that'd be the first solution to try.

This is going to be such a liberating device.
Thank you!

Reid



bobmcree said:
obviously you cannot use a resistive voltage divider to power a light bulb without throwing away lots of power. you could use a 3 terminal linear regulator like the LM318 but it would waste just as much power and 50w of heat is a lot to deal with and a lot of battery to waste.

the best solution is a switching voltage regulator. i have used the National LM2576HV which is a 3A device, and it is working fine to power the 30W HID lamp on my bike from my 48v battery. You can use these up to 60v in and adjust the output from 3-55v with a resistor pair. the regulation is better than 0.1% and they will do 4A with some extra heat sinking.

these "simple switcher" series parts from National make it possible to build a complete power supply for about $10, from the 5 pin part, a coil, a couple of caps, and a couple of resistors. they are very tolerant of part selection and layout, and work fine just wired together freehand and potted or glued in place. you do need to heat sink the regulator itself with a couple of square inches of surface area if using more than 2A. An aluminum case smaller than a cigarette pack will house the circuit and act as a suitable heat sink.

Rick K has some built for sale, but he has been hospitalized recently and i have no idea about the availability. the ones i have in quantity will accept up to 85v input, but the output is fixed at +/- 12v and they only supply 1.25A so they are good for powering a 13W HID but not your incandescent.

i would normally offer to build one, but we just bought a new house in oregon and will be moving over the next month or two, so i am not taking on any new projects. if you can solder you can build one from the datasheet on National's website.[/img]
Click to expand...
 
sorry, but rick k is in the hospital and i don't know how to contact him. my understanding is that he may be there for a long time.
 
Oh, I didn't understand how bad off he must be. Poor guy.
I hope he'll be OK soon again.

_________________
_______


Ah, so it's time for me to re-learn my rusty old vacuum tube electronics skills
and translate them to the (((((dreaded world of semiconductors))))
I have acquired excellent ability to mangle tiny things ever since my eyes are not so good anymore.

I'll do it, though: Get enough parts to make two converters and dedicate one to the 20W halogen headlight
and the other for the Unite motor blower; have the latter adjustable by a pot, maybe.

-this way too I'll have a spare unit if one ever fails.

On to search the parts now. Thank you, Bob!

_______________
________

Dep't of Hints :idea:
National LM2576HV

If ever there was a product with a market ready made,
it's this device of Bob's: all made up (((adjustable voltage for halogen headlight lumen efficiency))) potted in a tiny aluminum box,
itself mountable/heat-sinkable to a larger panel if desired

and on the shelf for sale to e-bikers.

power for horns, halogens, HID, 12V convenience outlets,
gimcracks, geehaws, whimidoodles.
 
Reid Welch said:
I'll do it, though: Get enough parts to make two converters and dedicate one to the 20W halogen headlight
and the other for the Unite motor blower; have the latter adjustable by a pot, maybe.

-this way too I'll have a spare unit if one ever fails.

On to search the parts now. Thank you, Bob!
Click to expand...

For >30V ->15V converters the good solution is 2-phase converter. This way you get peak current as much as half current of 1-phase converter.
This way you save the cells as this current is a part of the all load.
 
The simplest one that I've seen is here:
http://cache.national.com/ds/LM/LM2576.pdf

They make a 15v version, but you can also make it adjustable.

I think you could buy all the parts and assemble one. Sometimes they make what's called an evaluation board, which is a circuit board that will hold all the necessary parts. Those tend to be a bit expensive.
This circuit doesn't have many parts, so it's pretty easy.
 
Reid Welch said:
OK, I'm all ears. I am a dummy in this area.

Can you explain further how that works,
and possibly design a simple circuit?

Yes, I require 15V and preferably 15.5V for the halogen MR16 20W lamp.

Thanks
Click to expand...

2-phase high voltage converter have no simple circuit. It need external components (FETs) typically.
2-phase alternate draw current from input, so the peak current is 1/2 of 1-phase solution (each phase draw 50% average current ).
It is mostly usefull when you want higher current at lower voltage side. It work at higer efficiency so you dont need huge radiators.
If you need only 20-40W @ 15.5V simple switcher as LM2576 is good enough, but at 100W or more @15.5V 2-phase converter should be considered.
It's parts are not very expensive but is harder to mount at home definitely.

So the choice is yours. It depend how much power you will need by future loads.
My small out of topic:
2-phase could be as much powerfull as it could great reduce peak load at high tork low RPM conditions.
The most expensive parts at powerfull converters are capacitors. So it could be cheaper solution to smooth load as 16V low ESR capacitors are much cheaper then their counterparts at over 30V range.
But this solution would need controler that would work at high end low voltage as well. (At stall or low rpm could be switched at low voltage/extra high current mode). Controller's peak current could be the same but at lower voltage duty could be doubled so ripple loses could be greatly reduced at battery and motor sides.
 
Reid
whatever happened to the idea of using a spare cheap controller? pot to set v.
 
it is not necessary to use a complicated circuit with external fets to get 50w or less at 12-15v from 20-60v in.. you need just the simple LM2576 circuit with a coil and caps i showed in a previous photo.

i was considering putting together a kit, but i hear rick is being moved out of intensive care and is on his laptop now, and maybe i can arrange to get one of his modules for anyone who is interested. give me a couple of days to figure it out.

if i cannot find a way to sell the converters rick has already made, i will make a kit of parts available for $20 or so.

-bob
 
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