dc-dc converter

[Jay64]

I'm considering getting a dc-dc converter. What is a good one. Right now I have a 48v system and want to run the stock lights and stuff. But I am also thinking of upgrading to 72v. Is there one converter that could convert from 48v AND 72v to 12v???

 

[smithinparis]

Take a look at the maxim-ic website and look at the MAX5035. It has a very wide input voltage range (up to 76V I believe), and has a 12 volt output, but you will want to make sure it can handle your load.
The great thing about this Maxim converter is that you can order free samples to try. You'd have to provide all the external components of course, but you can't beat a free ic...

 

[frodus]

He's going to need alot more than 1A.... He'll need something in the range of 10-15A depending on if he's got dual headlights. Plus those converters aren't that efficient... not as efficient as switching converters. Kelly sells some that are wide range. So does electricmotorsport and thunderstruck.

get one of these:
http://cgi.ebay.com/RO-Associates-uV48-12-MicroVerter-DC-DC-Converter_W0QQitemZ310101151060QQcmdZViewItemQQptZBI_Electronic_Components?_trksid=p3286.m20.l1116

or these
http://cgi.ebay.com/DC-to-DC-Converter-48vdc-to-12-vdc-150w_W0QQitemZ170287329340QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item170287329340&_trksid=p3286.c0.m14&_trkparms=72%3A1205|66%3A2|65%3A12|39%3A1|240%3A1318|301%3A1|293%3A1|294%3A50

except, I don't know if 72v is ABSOLUTE max or not... so a fully charged pack of 72V might smoke it.... look at the datasheet.... if nothing else, they're cheap

 

[marty]

Look at this topic
Cheap DC-DC converters for over 60v input.
Now go find that box of old AC adaptors you been saving.
And yes do make sure it can handle your load.

 

[Jay64]

Look at this topic
Cheap DC-DC converters for over 60v input.
Now go find that box of old AC adaptors you been saving.
And yes do make sure it can handle your load.

I tried to post on that thread and I couldn't find the reply button. I found a few ac adapters that I have laying around, I'm sure I could find quite a bit more if I kept looking. But so far I haven't found any that say "switching" anywhere on them. Is one of these symbols for that by any chance?

 

[marty]

Jay,
Not sure what "switching" is?

Hook your 48V battery to the AC prongs that plug in the wall. Not sure is positive and negative matter? Now measure voltage that comes out. The 15V one should be good enough for your 12V stuff, but I don't think 1.33A is enough.

Hook 12V supply [use your car battery] to all the 12V stuff on your motorcycle. Turn everything on. Now measure the Amps that it all draws. Follow instructions on the multimeter. Your DC/DC converter should make more Amps then that. Not sure how much more is needed?

Great place to look at lots of DC/DC Converters is http://www.mouser.com Click on Power » DC/DC Converters & Regulators. See high prices. Get lower prices on Ebay.

 

[fechter]

But so far I haven't found any that say "switching" anywhere on them. Is one of these symbols for that by any chance?
View attachment 1

They usually don't say "switching" but the input voltage range is your clue here.

If the input voltage range goes from 100v to 240v, then it will be a switching supply.

A non-switching supply will have a very narrow input range.

 

[Jay64]

I actually already ordered a dc-dc converter. I got the one that was listed earlier-RO Associates uV48-12 MicroVerter DC-DC Converter. But I also was reading Fetcher's thread, listed above, and want to test these out. I have so many of them laying around, I figured I have to at least try them.

Thanks for the clarification Fetcher. I truely cannot express how much of an asset you are to this forum.

 

[Doctorbass]

Your idea of using switching (100-240V) is nice.. I already use that without any problem!!! mine started working wit a stable 12V Dc output at max current load (4A) at only 21VDC input !!!

So they work well!.. They are usually found with some 15" LCD monitor (the power supply that are exterior to the LCD) (box style)

It have some diode bridge at input and convert the normal AC voltage in rectified AC (so it's DC rith on the input capacitor)

That mean if you input Dc, the diode will conduct and it will work!

IT use a PWM.. so the pulse width vary depending on the voltage input.. for sure the pulse will be larger if voltage is low.. and the internal mosfet will conduct more time.. but it doesn't heat too much and still work for me!

You should be able to get one on ebay or at your local used computer store...

what is nice with that is that you can operate from 20 to 240VDC input!! that's just perfect!!..

NO MORE PROBLEM WITH THE LIMITED INPUT OF MOST DC-DC AT ONLY max 75V!!

Note.. some work some not.. it seems that theyr threshold input voltage level is not the same for all of those... I suggest you to bring a 36, 48 or higer voltage battery with you to test it before to buy!


Doc

 

[Jay64]

Would it be possible to hook up the output of a few of these together in parallel to get higher amps? I know, it might not be the most efficient way to get the power, but it could help to build a really cheap bike. I'm sure there are a lot of people out there like me who have a bunch of these laying around from old electronics. That could be a free mod for a junkyard type build.

 

[Doctorbass]

Would it be possible to hook up the output of a few of these together in parallel to get higher amps? I know, it might not be the most efficient way to get the power, but it could help to build a really cheap bike. I'm sure there are a lot of people out there like me who have a bunch of these laying around from old electronics. That could be a free mod for a junkyard type build.

ys you can.. if they have the same output voltage there is no problem.. if you get some that have 12V.. some at 14V some at 15V.. maybe you could put a diode in serie with each positive wire of them and then to parallel these input.. so the 15V would be the first to drive the max load.. then if the load become higher, the 15V will drop to 14V and the second 14V will share the current with the dropped 15Vto 14V.. .. etc.. but that is not the best solution.. getting many SAME voltage in parallel is better

Doc

 

[rkosiorek]

not all of those LCD adapters are created equall though. i bought a batch on ebay that were realy cheap. and they are not usable for our purpose.

these use an interesting technique to drop the line voltage down to 40V before going to the switching regulator. the line goes through a full wave rectifier then to a fet switch. the fet is controlled by a 40V zener. the rectified AC supplies a pulsing signal. the voltage starts at 0V and rises to the AC line voltage before dropping back down to 0V at either 100Hz or 120Hz depending on line frequency. in that period during which the voltage is 40V or less the fet conducts and the voltage is used to charge a capacitor. once the voltage rises over 40V the fet is turned off until the voltage drops below 40V on the back side of the pulse. the 40V power stored in the capacitor is what is used to power the switcher.

the switcher looks to be similar to one of the National Semiconductor simple switchers. the part number has been ground off. it is in a 5 lead TO220 case and is wired like a LM2576.

this circuit will not work on DC because the input voltage would always be over 40V and the fet would never turn on to charge the capacitor. the design relies on the input being a sinusoidal AC waveform to work.

but then i have used other ones from other sources that used a more conventional design that worked with a DC input voltage.

Rick

 

[Jay64]

I ended up going with one of these for right now.

From http://cgi.ebay.com/RO-Associates-u...Electronic_Components?_trksid=p3286.m20.l1116
Newbie questions, how do I hook up to this? Do I have to solder my wires to the posts?
What is the parallel on/off on the input side?
What are the +s, OG T, -s on the output side?

 

[markcycle]

I ended up going with one of these for right now.

From http://cgi.ebay.com/RO-Associates-u...Electronic_Components?_trksid=p3286.m20.l1116
Newbie questions, how do I hook up to this? Do I have to solder my wires to the posts?
What is the parallel on/off on the input side?
What are the +s, OG T, -s on the output side?

I'm using the same DC to DC and have no problems at all just be sure to heatsink it well. Also it needs a cap across its output to eliminate ripple and a annoying high frequency whistle. My voltage is 48 56 hot off the charger. I'm wondering if it will work with a 72 volt pack because a 72 volt pack is 84 hot off the charger

Mark

 

[Jay64]

markcycle, how did you hook up to the different pins? Would you mind posting a pic? And what did you mean by putting a cap across its output?

I just noticed on the side it has the specs. It states for input: 48 vdc, 7a. Does that mean I can only have 7a going in to it?

 

[rkosiorek]

to hook it up you need to either buy the special sockets that these plug into or solder on the wires.

as for how to hook it up the most accurate into always comes from the manufacturer and surprise it is available on the internet. here is a link to thier documentation page:

http://www.roassoc.com/appnotes.htm

in particular look at AP4 and AP13 to see how to use the remote on/off paralleling pin.

also the spec sheet will give info of how to hook up the remote sense wires.

http://www.roassoc.com/pdfs/uV48-12-164.pdf

rick

 

[markcycle]

markcycle, how did you hook up to the different pins? Would you mind posting a pic? And what did you mean by putting a cap across its output?

I just noticed on the side it has the specs. It states for input: 48 vdc, 7a. Does that mean I can only have 7a going in to it?

View attachment 1

No 7 amps is the Max current draw on the input. The out will do 20 amps at 12 volts I have used it almost up to that limit

Here is the connection picture I added a 1000uf electrolytic cap across the output. I also trimmed the uinit to 13.8 volts cause I use it to charge a Aux 12 volt battery

I connect the sense wire to the output pins at the unit just jumped across the pins with thin wire 22AWG wire and 10AWG to the load

 

[Jay64]

I tried to do the laptop charger theory. I first tried it with 4 batts at 50v and got nothing from the output of the charger. I added another battery to a total of 62v and still got nothing coming out of the charger. It is from my Dell laptop that got stolen recently. It is a 100-240v input. I tried taking a pic of it but can't get it to focus well enough to read the specs. Before I cut up the wires I tested it on 120 and it output 19v

 

[Doctorbass]

I tried to do the laptop charger theory. I first tried it with 4 batts at 50v and got nothing from the output of the charger. I added another battery to a total of 62v and still got nothing coming out of the charger. It is from my Dell laptop that got stolen recently. It is a 100-240v input. I tried taking a pic of it but can't get it to focus well enough to read the specs. Before I cut up the wires I tested it on 120 and it output 19v

some of these switching power supply will work and some will not work with lower than 100V dc ... you need to trial error many of them... mine that worked come from a 15" LCD monitor and start at 25V dc

Doc

 

[Jay64]

ok, cool. I thought maybe I did something wrong.

 

[fechter]

some of these switching power supply will work and some will not work with lower than 100V dc ... you need to trial error many of them... mine that worked come from a 15" LCD monitor and start at 25V dc

Doc

Yes, they vary widely. Some of them will only work with one polarity of input too (try reversing the input wires). I found one that would work down to 19 volts and up to 220v. Others take much more to get going. You just have to try them. It's good to pick a model that's been tested and known to work, but there are so many.

 

[Jay64]

Ok, I tried a couple more. One was from an old printer where the whole adapter slides into the port of the printer. I tried it on a 48v setup.
On 120v ac outlet it read 28v output (indicated it should have 30v output).
When I hooked it up to the 48v dc supply it read 28v, but then it consistently lost v at 0.1v. It seemed that the meter dropped lower about every second until it got down to 19.9v and I pulled it off the supply.

I then tried another one that I have no idea where I got it from, it has just been laying around in my closet for years. It has the prongs for the male plug coming right out of the adaptor. That one is rated for 15v output. On the 120v ac outlet it read 15v. I then hooked it up to the 48v dc supply and it read 15v! Woohoo! I think I found one that works! Unfortunately it is only 1.33 amp output, so I think that is a little low for what I need, but at least it is working. So, if I get a few of these that have matching v/a output I can hook them up in parallel to get the amps I need? That would be really awesome if that would work. Now I am really going to go digging through my closet and find all of them. Looks like I will have to test all of them individually though to make sure they work. I need to come up with a better dc supply plug to test them on to simplify things. I think I will wire in a regular ac outlet to the dc supply so that I can just plug each adapter straight into the supply without monkeying with it.

Fechter, thanks so much for this great idea. I know this has been said many times over, but you truely are a jewel on this forum.

 

[Jay64]

I found two for a rechargeable flashlight that I have. The specs state output: 6v dc 300mah. I figued I would hook two of them up in series, but when I tested them on 120v they indicate 11.1 v and 13.0 v output. wtf? When I plugged them into my 48v setup, they both output 7.4v.

 

[Doctorbass]

I found two for a rechargeable flashlight that I have. The specs state output: 6v dc 300mah. I figued I would hook two of them up in series, but when I tested them on 120v they indicate 11.1 v and 13.0 v output. wtf? When I plugged them into my 48v setup, they both output 7.4v.

Jay, this is because these little power supply are not regulated and probably class II regulation spec.. so their floating (no load) voltage is higher than the nominal voltage with load... if they indicate that at 300mA load they output 6V that mean at 150mA load they will probably do around 9V...

so this is normal but preferable...

Doc

 

[Almasi]

I tried to do the laptop charger theory. I first tried it with 4 batts at 50v and got nothing from the output of the charger. I added another battery to a total of 62v and still got nothing coming out of the charger. It is from my Dell laptop that got stolen recently. It is a 100-240v input. I tried taking a pic of it but can't get it to focus well enough to read the specs. Before I cut up the wires I tested it on 120 and it output 19v

some of these switching power supply will work and some will not work with lower than 100V dc ... you need to trial error many of them... mine that worked come from a 15" LCD monitor and start at 25V dc

Doc

I tried 2 different one, first one that I don't need only work with 90 Volt +...

Then I try the second one (my current laptop charger) works from 36 volt and up...to bad that's the one I need for my laptop!

I will need to find another one

Robin