# 12 volts to 48 volts for an electric bicycle

Started by September 18, 2012
```I got a used 36-volt Crystalyte hub motor and controller from Craigslist.  (The guy who sold it to me said they can take 72 volts, but I'm still trying to confirm that from their website, which is a bit skimpy.  Looks like I'll have to email them.)

Motor = 400 X4 (408)
http://www.crystalyte.com/

I tried 48V (4x 12v SLA batteries, 8 A-h each), and the bike worked fine for about 3 miles, but left me to pedal the remaining 9 miles home from work.

Since the 12V 8 A-h batteries are \$33 each from Home Depot, I wondered about returning them and buying a (heavy!) 12V, 85 A-h deep cycle battery from Costco (only \$68).  If I go that route, I'll need a DC-DC converter, converting 12V to 48V.

I'm thinking of the LT1339, and apparently the output voltage is set by Vout = 1.25 (1 + R2/R1), from page 9 of the datasheet.
http://cds.linear.com/docs/Datasheet/1339fas.pdf

Is the output current set by what ever the input supply can provide?

This 555 circuit looks like fun too.
http://www.dos4ever.com/flyback/flyback.html

Since I want the output voltage to be 4x the input voltage, is a duty cycle of 75% correct?

Thanks,

Michael
```
```On Tuesday, September 18, 2012 6:20:47 PM UTC+2, mrda...@gmail.com wrote:
> I got a used 36-volt Crystalyte hub motor and controller
> from Craigslist.

Huh? If it says 36 Volts then it's 36 Volts.
72V will make it spin a lot faster and heat
it up more. Possibly burning it out.

> (The guy who sold it to me said they can take 72 volts,
> but I'm still trying to confirm that
> from their website
>

Sellers tend to say things like that, yes.
If it was me I'd have confirmed it before
handing over the money.
```
```On Sep 18, 12:20=A0pm, mrdarr...@gmail.com wrote:
> I got a used 36-volt Crystalyte hub motor and controller from Craigslist.=
=A0(The guy who sold it to me said they can take 72 volts, but I'm still t=
rying to confirm that from their website, which is a bit skimpy. =A0Looks l=
ike I'll have to email them.)
>
> Motor =3D 400 X4 (408)http://www.crystalyte.com/
>
> I tried 48V (4x 12v SLA batteries, 8 A-h each), and the bike worked fine =
for about 3 miles, but left me to pedal the remaining 9 miles home from wor=
k.
(About fifteen minutes of power?  (Assuming ~15 mph) so about 32 amps
of current?

>
> Since the 12V 8 A-h batteries are \$33 each from Home Depot, I wondered ab=
out returning them and buying a (heavy!) 12V, 85 A-h deep cycle battery fro=
m Costco (only \$68). =A0If I go that route, I'll need a DC-DC converter, co=
nverting 12V to 48V.

Ahh that looks like it will almost get you home.  But if you crash
with the deep cycle battery strapped to your bike you may spill acid
on yourself.

>
> I'm thinking of the LT1339, and apparently the output voltage is set by V=
out =3D 1.25 (1 + R2/R1), from page 9 of the datasheet.http://cds.linear.co=
m/docs/Datasheet/1339fas.pdf
>
> Is the output current set by what ever the input supply can provide?

There is a current sense resistor.  You'll need to pick the right
FET's!
(But I don't know much about power DC-DC converters.)

Digikey has 12V/ 33 A-h SLA's... not cheap though.

>
> This 555 circuit looks like fun too.http://www.dos4ever.com/flyback/flyba=
ck.html
>
> Since I want the output voltage to be 4x the input voltage, is a duty cyc=
le of 75% correct?
>
> Thanks,
>
> Michael

```
```On Tuesday, September 18, 2012 11:33:11 AM UTC-7, George Herold wrote:
> On Sep 18, 12:20=A0pm, mrdarr...@gmail.com wrote:
>=20
> > I got a used 36-volt Crystalyte hub motor and controller from Craigslis=
t. =A0(The guy who sold it to me said they can take 72 volts, but I'm still=
trying to confirm that from their website, which is a bit skimpy. =A0Looks=
like I'll have to email them.)
>=20
> >
>=20
> > Motor =3D 400 X4 (408)http://www.crystalyte.com/
>=20
> >
>=20
> > I tried 48V (4x 12v SLA batteries, 8 A-h each), and the bike worked fin=
e for about 3 miles, but left me to pedal the remaining 9 miles home from w=
ork.
>=20
> (About fifteen minutes of power?  (Assuming ~15 mph) so about 32 amps
>=20
> of current?

Yes, about 15 minutes, come to think of it.  Kind of scary to think I burne=
d through 384 watt-hours in just 15 minutes.  Stop-and-go traffic (lots of =
stop-signs in the neighborhood).  The motor was *very* warm to the touch af=
terwards, too.  Loads of fun to bike home with heavy SLAs (and a heavy hub =
motor to boot).  =3D)

I bought some more SLAs so I have 6 total (4 new ones, along with 2 old one=
s I've been charging every month to keep them alive).  Since another poster=
mentioned running the motor beyond spec is not advisable, I suppose I coul=
d have two banks of batteries in parallel.  That's not a bad idea, is it?

> > Since the 12V 8 A-h batteries are \$33 each from Home Depot, I wondered =
about returning them and buying a (heavy!) 12V, 85 A-h deep cycle battery f=
rom Costco (only \$68). =A0If I go that route, I'll need a DC-DC converter, =
converting 12V to 48V.
>=20
>=20
>=20
> Ahh that looks like it will almost get you home.  But if you crash
>=20
> with the deep cycle battery strapped to your bike you may spill acid
>=20
> on yourself.

Yeah, good point... even just tipping the bike over would be pretty nasty. =
And that deep-cycle battery is *heavy*.

...

> > Is the output current set by what ever the input supply can provide?
>=20
>=20
>=20
> There is a current sense resistor.  You'll need to pick the right
>=20
> FET's!

Oh, yay.

> (But I don't know much about power DC-DC converters.)
>=20
>=20
>=20
> Digikey has 12V/ 33 A-h SLA's... not cheap though.

Yeah, I'm aiming for cheap.  That was the motivation for looking at an off-=
the-shelf deep cycle battery.

I would go for a motorcycle, but (1) they're kind of noisy, and I'd rather =
save my hearing for enjoying metal music, and (2) in this city of mine the =
drivers are half-insane anyway and I'm sure I'll die on a motorcycle.  At l=
east with a motorized bicycle I can stay in the safer bike lane.

```
```On Tuesday, September 18, 2012 10:44:14 AM UTC-7, fungus wrote:
> On Tuesday, September 18, 2012 6:20:47 PM UTC+2, mrda...@gmail.com wrote:
>=20
> > I got a used 36-volt Crystalyte hub motor and controller
>=20
> > from Craigslist.
>=20
>=20
>=20
> Huh? If it says 36 Volts then it's 36 Volts.
>=20
> 72V will make it spin a lot faster and heat
>=20
> it up more. Possibly burning it out.

Gotcha, thanks.

From looking it up on the manufacturer's website, the controller looks like=
it may take 72V, but you're right, the motor is def. rated at 36V.

> > (The guy who sold it to me said they can take 72 volts,
>=20
> > but I'm still trying to confirm that
>=20
> > from their website
>=20
> >=20
>=20
>=20
>=20
> Sellers tend to say things like that, yes.
>=20
> If it was me I'd have confirmed it before
>=20
> handing over the money.

Good point.  I was watching the prices on Craigslist for some time though, =
and this one was offered at somewhat below the average price, enough so tha=
t I decided to take a risk and try it out.  Sure, the throttle control need=
s a new spring, but at least the thing works.  Or, well, it is dependent on=
battery capacity. =20

```
```...

> Digikey has 12V/ 33 A-h SLA's... not cheap though.

http://www.digikey.com/product-detail/en/BP28-12-B1/522-1015-ND/653336

12V, 28 A-h for \$79.  24 A-h (3x batteries @\$33) from Home Depot would be \$99.  But, wow, 21 lbs, huh.  Would need three of them... (or, again, a DC-DC converter.)
```
```On Tue, 18 Sep 2012 09:20:46 -0700 (PDT), mrdarrett@gmail.com wrote:

>I got a used 36-volt Crystalyte hub motor and controller from Craigslist.  (The guy who sold it to me said they can take 72 volts, but I'm still trying to confirm that from their website, which is a bit skimpy.  Looks like I'll have to email them.)
>
>Motor = 400 X4 (408)
>http://www.crystalyte.com/
>
>I tried 48V (4x 12v SLA batteries, 8 A-h each), and the bike worked fine for about 3 miles, but left me to pedal the remaining 9 miles home from work.
>
>Since the 12V 8 A-h batteries are \$33 each from Home Depot, I wondered about returning them and buying a (heavy!) 12V, 85 A-h deep cycle battery from Costco (only \$68).  If I go that route, I'll need a DC-DC converter, converting 12V to 48V.
>
>I'm thinking of the LT1339, and apparently the output voltage is set by Vout = 1.25 (1 + R2/R1), from page 9 of the datasheet.
>http://cds.linear.com/docs/Datasheet/1339fas.pdf
>
>Is the output current set by what ever the input supply can provide?

---
No.

The output current will be whatever the load wants, with the upper
limit dictated by the voltage dropped across Rsense as described on
page 10 of the data sheet, just above "Output Voltage Programming".

>
>This 555 circuit looks like fun too.
>http://www.dos4ever.com/flyback/flyback.html
>
>Since I want the output voltage to be 4x the input voltage, is a duty cycle of 75% correct?

---
Not necessarily.

Take a look at the equations in the article.

\
--
JF
```
```On Sep 18, 2:45=A0pm, mrdarr...@gmail.com wrote:
> On Tuesday, September 18, 2012 11:33:11 AM UTC-7, George Herold wrote:
> > On Sep 18, 12:20=A0pm, mrdarr...@gmail.com wrote:
>
> > > I got a used 36-volt Crystalyte hub motor and controller from Craigsl=
ist. =A0(The guy who sold it to me said they can take 72 volts, but I'm sti=
ll trying to confirm that from their website, which is a bit skimpy. =A0Loo=
ks like I'll have to email them.)
>
> > > Motor =3D 400 X4 (408)http://www.crystalyte.com/
>
> > > I tried 48V (4x 12v SLA batteries, 8 A-h each), and the bike worked f=
ine for about 3 miles, but left me to pedal the remaining 9 miles home from=
work.
>
> > (About fifteen minutes of power? =A0(Assuming ~15 mph) so about 32 amps
>
> > of current?
>
> Yes, about 15 minutes, come to think of it. =A0Kind of scary to think I b=
urned through 384 watt-hours in just 15 minutes. =A0Stop-and-go traffic (lo=
ts of stop-signs in the neighborhood). =A0The motor was *very* warm to the =
touch afterwards, too. =A0Loads of fun to bike home with heavy SLAs (and a =
heavy hub motor to boot). =A0=3D)
>
> I bought some more SLAs so I have 6 total (4 new ones, along with 2 old o=
nes I've been charging every month to keep them alive). =A0Since another po=
ster mentioned running the motor beyond spec is not advisable, I suppose I =
could have two banks of batteries in parallel. =A0That's not a bad idea, is=
it?
>
> > > Since the 12V 8 A-h batteries are \$33 each from Home Depot, I wondere=
d about returning them and buying a (heavy!) 12V, 85 A-h deep cycle battery=
from Costco (only \$68). =A0If I go that route, I'll need a DC-DC converter=
, converting 12V to 48V.
>
> > Ahh that looks like it will almost get you home. =A0But if you crash
>
> > with the deep cycle battery strapped to your bike you may spill acid
>
> > on yourself.
>
> Yeah, good point... even just tipping the bike over would be pretty nasty=
. =A0And that deep-cycle battery is *heavy*.
>
> ...
>
> > > Is the output current set by what ever the input supply can provide?
>
> > There is a current sense resistor. =A0You'll need to pick the right
>
> > FET's!
>
> Oh, yay.
>
> > (But I don't know much about power DC-DC converters.)
>
> > Digikey has 12V/ 33 A-h SLA's... not cheap though.
>
> Yeah, I'm aiming for cheap. =A0That was the motivation for looking at an =
off-the-shelf deep cycle battery.
>
> I would go for a motorcycle, but (1) they're kind of noisy, and I'd rathe=
r save my hearing for enjoying metal music, and (2) in this city of mine th=
e drivers are half-insane anyway and I'm sure I'll die on a motorcycle. =A0=
At least with a motorized bicycle I can stay in the safer bike lane.- Hide =
quoted text -
>
> - Show quoted text -

Biking is good for you... exercise and all that.  You could always try
one of those scooter/ Vespa things.  Lots more energy density in
gas.

George H.
```
```On Tuesday, September 18, 2012 11:33:11 AM UTC-7, George Herold wrote:

> (About fifteen minutes of power?  (Assuming ~15 mph) so about 32 amps
>=20
> of current?

Looks like even an 85 A-h 12V deep-cycle battery won't be sufficient, huh.

4x12V @ 8 A-h got me 3 miles.  That's 128 W-h/mile.  Distance to travel (on=
e-way, assuming I can charge at work and at home) is 12 miles.  So I'll nee=
d 1536 W-h.  That's 3 12V batteries at 43 A-h, or one 12V battery at 128 A-=
h (assuming a DC-DC converter at 100% efficiency).

Then again, since I was running a 36V motor at 48V, I was probably losing m=
ore energy to heat than I would otherwise... maybe 128 W-h/mile is a bit hi=
gh...=20

More research needed!

Thanks y'all.
```
```On Tuesday, September 18, 2012 12:18:38 PM UTC-7, George Herold wrote:

...

> Biking is good for you... exercise and all that. =20

Yeah, I know!  I can pedal the 12 miles in about 58 minutes.  Not every day=
though.  I thought an electric bike would allow me to do it every day, sav=
ing me the gasoline.  (Round-trip in a Toyota Camry burns through about a g=
allon of gas; 24 mpg city is about right.)

> You could always try
>=20
> one of those scooter/ Vespa things.  Lots more energy density in
>=20
> gas.

No argument there!  I was even thinking of those 2-stroke bicycle engine ki=
ts for around \$300 or so.  Then I remembered when I use the weed-whacker on=
the lawn I like to wear hearing protection since those engines are kind of=
loud...

I would totally go for a Honda Trail 90 (they're about \$600 on Craigslist),=
but (1) I'd have to contend with the maniac drivers who apparently are una=
ware of basic traffic laws, and (2) I'd need to get a motorcycle license.

Thanks!

Michael
```