Author Topic: Voltage question?  (Read 22208 times)

Offline Sundsvall

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Voltage question?
« on: September 04, 2010, 09:27:24 PM »
Hi,

The delivery times on some parts to the summer bike project has been extraordinary long and I’ve change my mind a few times resulting in new orders. So I was just going to connect the CA to my winter bike since I felt like I had to do something and suddenly the she was spread all over the garage. My old bike light was plenty of LED’s in the junction box for the controller and when I found a different place for the controller the light went of with the junction box.

Now I’m thinking about to buy two of these bike lights http://www.dealextreme.com/details.dx/sku.30864 but don’t want to feed them with the supplied 8,4 volt battery pack. I’ve bought a 24 V frog style battery from GM and my intention is to use this instead.

How do I reduce the voltage from my froggie to the right voltage?
Is it possible to assume the correct voltage range the light can handle?

I’ve found a switch regulator (TSR 1-2490) for €10 but that one could only manage 1 A and these lights are marked as 10 W each. I don’t even know if a switch regulator is useable.

Peter
Midsummer sun = up 02:54   down 22:51   angle 51,0° :)
Midwinter sun =    up 09:19   down14:18   angle 4,2° :(
Mean annual temperature = 3,1°C

Offline muzza.au

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Re: Voltage question?
« Reply #1 on: September 04, 2010, 10:58:59 PM »
G'day Peter,

Check out this thread where I did the same thing and how I did it: http://goldenmotor.com/SMF/index.php?topic=1744.0

Muzza.au

ps. I've sold that bike now, so currently I have only 2 old incomplete e-bikes I never got around to finishing. I currently use a car.  :-\
« Last Edit: September 04, 2010, 11:01:20 PM by muzza.au »

Offline GM Brazil

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Re: Voltage question?
« Reply #2 on: September 05, 2010, 12:59:42 AM »
What is the main difference between a Voltage regulator like the 7805 or LM317 from a DC/DC converter???

Offline Bikemad

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Re: Voltage regulators and DC-DC converters
« Reply #3 on: September 05, 2010, 02:00:46 AM »

I'm pretty sure the DC-DC converter is much more efficient, which basically means it will consume less current, and generate less heat, whilst still providing the same output as a simple voltage regulator.

Some DC-DC converters are capable of producing an output voltage which is considerably higher then the original input voltage, whilst others are used to ensure complete electrical isolation between the input and the output (just like a transformer does with AC voltage).

More information can be found here.

Alan
 

Offline Sundsvall

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Re: Voltage question?
« Reply #4 on: September 05, 2010, 07:50:46 AM »
I think that DC-DC converter would fit my needs. :) However, I’ve now tried to buy it twice and both times got “Sorry, we were not able to complete your purchase” and a confirmation mail that the purchase is Ok. There’s also a mail from myself with a confirmation that I have cancelled the pending payment. In my PayPal account the payment is reversed. :(

Thank you Alan,
for the link. There’s a lot of reading in the DC-DC converter tutorial.
for the tip of the converter. They’ve provided a huge amount of information along with it. I really hope I’ll be able to buy it.

Peter
Midsummer sun = up 02:54   down 22:51   angle 51,0° :)
Midwinter sun =    up 09:19   down14:18   angle 4,2° :(
Mean annual temperature = 3,1°C

Offline Leslie

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Re: Voltage question?
« Reply #5 on: September 06, 2010, 02:21:51 AM »
There is buck and boost configs with the switching voltage regulators.

Buck winds down the voltage around an inductor and spits out more current.

Boost winds up the current through an inductor and spits out more volts.


Boost is more efficient and see the conversion good up to 90% efficiency.

Buck is pretty efficient and see the conversion good up to around 80% efficiency.

You need Buck.


Ive been building my switchers and Ive almost given up as I am finding the HV chips I am buying wont do any more than 45v which isnt HV.  60v is HV.

I think AE is selling reprinted or clones LM2576 chips.  I made one switcher that lasted a few months and since then they all spit out the fet in them as soon as I put 50v in them.

Its sad because the LM2576 switcher IC can output up to 3 amps.  Think, you can run a 12v 30 watt halogen @ 3 amps off a 54v supply and only draw 600 ma from your pack doing this.  

I cant find a decent source for the HV IC and Im beginning to wonder if any exist to buy online with a cheap delivery service.

As soon as I can make a reliable HV DC to DC converter that does 80% efficiency I will make some up and sell them at cost.

I want to avoid the LM317t stage in my build.

Linear regs just burn off energy.  Like if you want 15v output from a 30v input voltage and draw 500ma.  You minus 15v from 30v, =15v and times the drop by the current draw.

So 15v X .5 amps is 7.5 watts.  The package can handle 25 watts from memory and the LM338 can do 50 watts I would consider much under this rating for reliable performance.  Man they can get hot and current slows when they do.   by the end you are using 15 watts the whole circuit to run a 7.5 watt device.

Even so!

Muzza solution is best ATM, not easy to do as you see all the work involved.  The linear regs are used for controllers often as they are very reliable and wont give up when they are used properly.  Your FETS will die and do die before your linear regulator will.




Limits to these Linear regs are as follows.


The LM317T can handle 14v V drop and above 3v V drop at 1.5 amps. 4.5~21 watts.

The LM317T can only handle a V drop of 37v under 600ma and will burn 22watt of power just doing it.



The LM3338 can handle 9v V drop and above 3v V drop at 5 amps. 15~45 watts

The LM338 can handle a V drop of 37v under 1. amps and burn 48 watts doing this. 44.4 watts


At least allow 3v drop for reference voltages and diode transistor drops inside the IC for rock solid voltage regulation to occur..

Add heat sink can improve both performance and efficiency to a small degree but can increase reliability substantially..

If your current draw is constant a power resistor could do the job just as well.

My switchers can do 45v to 3.2v output 3 amps and use 160ma to do so.

30% loss equates to 20ma at 45v = lose enough to 1 watt.

The switcher is a multitude more efficient.  My switchers barely get warm doing 41v drop..
« Last Edit: September 06, 2010, 02:58:34 AM by 317537 »

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Offline Leslie

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Re: Voltage question?
« Reply #6 on: September 06, 2010, 05:02:40 AM »
ATM I get 10 of these LM2576 HVT ADJ Adjustable regs from Asian Engineer for around $15 but I just migh try a digikey part.


The digikey parts are $6.50 so I will get ten of them depending on the delivery fee. ATM Fedax 40 buck fee for 30 odd grams of IC is just unacceptable.

The amount I want shouldnt cost more than a postage stamp.

Can anyone here get these authentic LM2576 HVT chips from a local supplier?.

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Offline Sundsvall

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Re: Voltage question?
« Reply #7 on: September 06, 2010, 07:14:07 AM »
As the purchase on the converter didn’t work, I ordered the bike light from Deal Extreme and the PayPal account worked as supposed. I therefore made a new attempt to order from eBay but with the same result.

I really need some help how to get my hands on one of these.

Leslie, I can by the LM2576HVT-ADJ with a shipping cost of $20, but instead 10 of them are $75.

Peter
Midsummer sun = up 02:54   down 22:51   angle 51,0° :)
Midwinter sun =    up 09:19   down14:18   angle 4,2° :(
Mean annual temperature = 3,1°C

Offline Leslie

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Re: Voltage question?
« Reply #8 on: September 06, 2010, 08:53:15 AM »
We can do this tomorrow,

They must be authentic or else we waste my money.

If you want I pay you tomorrow by Paypal, you can buy them for me and send them to my address.  If you want you can keep one and try make this regualtor.

I know these chips I am buying are not authentic as all I need do is connect the input pins to the 52v and the go sizzzz bang and anything over 45v. Where the authentic LM2576 HVT chip should handle this input.

I can build two of these regulators and send you one, I can make it 85% efficient to waht voltage and current you decide.

Variable voltage adjustment will not be as efficient but within 6v or so will be fine.

You can give me some fun work to do while I wait 4o days for my Pie.

Cheers.

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Offline MonkeyMagic

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Re: Voltage question?
« Reply #9 on: September 06, 2010, 11:06:23 AM »
Hey guys

I use this for some electronics. I needed high amp 3.3v for cree LED's and 12v for other accessories. I just tap a 7805 of the 12v to get 5v for other stuff.
http://cgi.ebay.com/DC-DC-Converter-60W-48V-Triple-out-3-3V-12V-12V-/370390229384?pt=LH_DefaultDomain_0&hash=item563cfa6188

But it's available in 100W too if you want to take a disco with you on your bike or something lol
http://cgi.ebay.com.au/DC-to-DC-Converter-100W-48V-3-3V-12V-12V-Very-Nice-/370182263786?pt=LH_DefaultDomain_0&hash=item56309513ea

Would one of these help you out?


Cheers

Offline Leslie

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Re: Voltage question?
« Reply #10 on: September 06, 2010, 06:13:55 PM »
Hey guys

I use this for some electronics. I needed high amp 3.3v for cree LED's and 12v for other accessories. I just tap a 7805 of the 12v to get 5v for other stuff.
http://cgi.ebay.com/DC-DC-Converter-60W-48V-Triple-out-3-3V-12V-12V-/370390229384?pt=LH_DefaultDomain_0&hash=item563cfa6188

But it's available in 100W too if you want to take a disco with you on your bike or something lol
http://cgi.ebay.com.au/DC-to-DC-Converter-100W-48V-3-3V-12V-12V-Very-Nice-/370182263786?pt=LH_DefaultDomain_0&hash=item56309513ea

Would one of these help you out?




Cheers


Shame the Cree clones run at 3.5v nice but 18 amps worth of crees could have you blind the people in the next country or attract aliens from a distant world wondering how you illuminated the dark side of universe with a led array.

Yeah Peter take a rain check on ordering those LM2576's and get one of these.

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Offline Sundsvall

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Re: Voltage question?
« Reply #11 on: September 06, 2010, 07:36:41 PM »
Hey guys

I use this for some electronics. I needed high amp 3.3v for cree LED's and 12v for other accessories. I just tap a 7805 of the 12v to get 5v for other stuff.
http://cgi.ebay.com/DC-DC-Converter-60W-48V-Triple-out-3-3V-12V-12V-/370390229384?pt=LH_DefaultDomain_0&hash=item563cfa6188

But it's available in 100W too if you want to take a disco with you on your bike or something lol
http://cgi.ebay.com.au/DC-to-DC-Converter-100W-48V-3-3V-12V-12V-Very-Nice-/370182263786?pt=LH_DefaultDomain_0&hash=item56309513ea

Would one of these help you out?


Cheers

No, the lights are for my winter bike which has a 24 V system. The output voltage are more complicated as the supplied battery pack gives 8,4 V fully charged. The lights must allow the voltage to droop a few volts without cutting off and therefore they have to accept a range from maybe 6 – 10 V, but I’m only guessing here.

If I feed them with higher voltage would the current be lower? ???

I have to get my winter bike back in one piece again as the missing parts to the summer bike soon will be here and then she’ll have all my attention.

The LM2576’s I’ve found are at Sweden’s largest distributor on electronic stuff and I would be very surprised if they sell anything non-authentic.

https://www.elfa.se/elfa3~ex_en/elfa/init.do?init=1&shop=ELFA_EX-EN#item=73-270-26;

Peter
Midsummer sun = up 02:54   down 22:51   angle 51,0° :)
Midwinter sun =    up 09:19   down14:18   angle 4,2° :(
Mean annual temperature = 3,1°C

Offline Leslie

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Re: Voltage question?
« Reply #12 on: September 06, 2010, 08:28:52 PM »
Your light says "Digital Regulated 1000mA Current Output"

You could get the 12v and run two lights in series. It seems that the output being regulated should make the divide for two lights in series be balanced.


You do a voltage divider with two resistors over the terminals that would insure they balance the volts between them.

We can still do the LM2576 thing.  And we don't need the HV chips for your system.

But I can make it run from 6v to 60v with a proper LM2576htv chip and still feed your two amps required to run two of those lights.

I need to replace one of my PING BMS today so it can happen next week.

I can still build you one from my chips here if I have any left but I can only guarantee a 45v input.

I have one in my roof running my led 3.3v system and its been going for 6 months now non stop I don't switch it off,  It supplying about 200 * 15 ma leds.  About 3 amps.  Steps down from 15v max, but can do 40v to 3.3 in a heart beat.
« Last Edit: September 06, 2010, 08:32:35 PM by 317537 »

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Offline Sundsvall

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Re: Voltage question?
« Reply #13 on: September 06, 2010, 09:08:31 PM »
I don’t understand the “Digital Regulated 1000mA Current Output” thing, I thought it was from the battery pack since the lights have no output.

Is it applying to the LED’s driver?
I thought these LED’s only could manage 350 mA, but I’m apparently a noob.

Quote
You could get the 12v and run two lights in series. It seems that the output being regulated should make the divide for two lights in series be balanced.


You van do a voltage divider with two resistors that would insure they balance the volts between them.

My winter bike have lost the fishing box (read: battery box) and the oversized junction box. This is going to give her a much neater look since I’m trying to fit everything in the froggie. The available space is NOT good though and your idea is therefore very interesting.

Could you please explain the voltage divider to me as I don’t understand where to put the resistors or the size of them?

Peter

edit:
Btw, my link didn’t open the item directly but the item number is in the link so you can just search for that. I checked the terms on the site and the shipping cost outside EU was €20 but it would be easy for you to order directly from them.
« Last Edit: September 06, 2010, 09:19:21 PM by Sundsvall »
Midsummer sun = up 02:54   down 22:51   angle 51,0° :)
Midwinter sun =    up 09:19   down14:18   angle 4,2° :(
Mean annual temperature = 3,1°C

Offline Leslie

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Re: Voltage question?
« Reply #14 on: September 07, 2010, 01:12:41 AM »
If I put 50v on a 2.5 v led but restrict the amps to the Leds specification say 20 ma, this Led will run all year on a 50v supply.

Try it.

Buy a red 2.4v 20ma led light.  Lets forget the voltage.

You have a 24v pack reads 28v fully charged.

Find the resistance need to run 20ma at 28v.

So 28v/.020A=1400 ohms  The entire circuit we will design can not exceed or be less than 1400 ohms

Buy a red 2.4v 20ma led light.  Find its on resistance,

2.4v/.02 amps= 100 ohms.

Now subtract 100 ohms for 1400 ohms and you have 1300 ohms.  Write this 1300 ohm number down.

Now we need to find the watt resistor needed We do this easy because we know our led is 2.4v so let us do this one easy.

The resistor will make a voltage drop and divide the volts so the led doesn't get too much volts or amps so we subtract the volts we have with the led from the battery input.

28v-2.4v= 25.6v@20ma  The resistor will drop 25.6v

Watts = VXI=W  25.6v *20ma =.51 watts.  You will need more than a half watt resistor to handle the heat the resistor need to dissipate to make the voltage drop.

Buy a 1300 ohm 1 watts resistor and connect it to the battery in a series circuit with the led and the led will run nice.

The same applies with digital current regulation but this is much better.  If the circuit sees a 8v or 4v input it will not allow anymore current to the led than 1 amp and the led will not go bright or dim.

This is better than a resistor as your pack will run out and the resistor becomes too high.

Current follower circuits do just this.  They can run single devices on many voltages without any voltage regulation all based upon what current the device needs.

We can do this whole math not knowing the voltage requirements or the Led too.  Enough for now.


This is an analogue current follower.



The equasion is 1.25v/I= the resistor you need

This calculator makes it easier as it tells you watts you need too..

http://www.reuk.co.uk/LM317-Current-Calculator.htm

So say you want one amp to pass this circuit. 1.25/1=1.25ohms

See the resistor there you need a 1.25 resistor for this to work 1 amps..  

You can then put a 39v to 5v supply on a 2.4v led and the led will run perfectly through the LM317t.  

Very easy to do.  

So really your question has now become one of current not voltages.

Buy your led lights and measure how much current it used by each light at 6v and mark it on the lights so you don't get mixed up.

We an work from there and make you lights run in perfect balance in series at 12v..
« Last Edit: September 07, 2010, 01:29:45 AM by 317537 »

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