24V System Question....

Discussion in 'Electrical' started by sangesf, Feb 12, 2009.

  1. sangesf

    sangesf Banned

    I have this current setup....

    I have this 24v battery on my electric bicycle and connected to it is an inline Digital Volt/Amp Meter (with shunt) and of course it connects to the controller (for the motor) and I want to connect a DC to DC converter.

    The dc to dc (24to12) converter would be for Turn Signals (LEDs), radio, lighter, lighter sockets and a few other low watt 12v items that I would like to hook up. (total watts to be used/drawn = 100 watts) I'm hooking up an illuminated rocker switch (12v kind, which I already bought and can install no problem.) to turn off all those 12v accessories when I'm not using them.

    Now to the problem/issue..
    What I also wanted (needed?) to do was to setup an illuminated rocker (24v) switch, after the battery, to disconnect the battery when not in use (e.g. I'm in the store, at a library, etc) and which would effectually disconnect the DC to DC converter when I'm ready to charge the battery...

    (The switch's most important use would be when charging, because it would disconnect the DC to DC converter from the circuit while I charged the battery - {The same power wires that go to the controller to power the bike, are the same wires that I (have to) use to charge the battery} and I didn't want to have the DC to DC converter still connected when charging)
    Trying to charge the battery with the DC to DC converter still connected would cause problems, right?

    Anyone's .02?

  2. cooltoy

    cooltoy Member

    Not sure but with "balanced" charging at low amps and your converter always being on seems like a bad idea. Does a converter that is not powering anything suck juice?
  3. loquin

    loquin Active Member

    Some. Depends upon the converter as to how much. Some converters HAVE to pass a minimum amount of power; in these designs, there will usually be a built-in shunt resistor to load the converter with the minimum load.
  4. sangesf

    sangesf Banned

    When I have to charge the battery, I will have the power lead "open" on the 12v side of the converter, so I'm not worried about that.... I was just curious if the converter would be either a hindrance to the charging or would it be damaged or be a damaging component to the charger/battery DURING charging.

    The point being, either way, I need to get a 24v at least 25a switch. My question is now, where do I find one, ESPECIALLY one that has illumination too.
  5. duivendyk

    duivendyk Guest

    If you did not have the illuminated switch, which requires 12 V ,you could use an ordinary switch and use it to disconnect the dc/dc convertor from the battery when you want to cut the load,this is also more efficient.You could rig up an indicator light to tell you that the 12V is enabled.If you worry about the dc/dc convertor being connected while charging your battery,why worry?, essentiaLly the same situation already arizes when you use your 12V switch to turn off the 12V loads !I don't think it will do any harm at all to leave the dc/dc convertor permanently connected to the battery,but it would take a bit longer to charge it,that's all.Does it have an on/off switch?BTW 100 Watt ,4 Amp at 24V seems like a lot of power to me/
    Last edited by a moderator: Feb 12, 2009
  6. sangesf

    sangesf Banned

    That's what I'm looking for.. a 24v switch... I need it to be rated for at least 25a. (preferably illuminated)

    I haven't hooked up anything yet, I'm asking questions before I start :)

    I don't think it will create a problem either, but asking just to make sure.

    No it doesn't have an on/off switch.. that's what I'm wanting the 24v 25a switch for, to control power to the converter and to a couple of other 24v electronics.

    100 watts is the MAX load I would have at any one time on the 12 v side of the converter and at that point it's actually 8.3 amps. The converter is rated at 15a and I'm using a 24v 60ah LiFePO4 battery to run everything on my bicycle. It's not a problem, because I can get 50 amps continuous (70amp max) from the battery and the most my Bike uses at ANY time is 35a so, 35a max for motor and 15a max for DC-DC converter so I'm not worried about power. (Or should I?)

    On a side note, I'm currently getting 54 miles distance on the bike and am expecting to get ~40-45 miles once all of the electronics are hooked up and working. (but i'm also getting an additional 24v motor(250w) and battery for the front at a later date.)
  7. duivendyk

    duivendyk Guest

    What if you used a 30 Amp breaker, like you find in house entry panels,they have a bimetal spring device that you cock,a large enough slug of current will heat it up enough to trip the thing.It's a quick disconnect so I quess it would survive diconnecting 24 V dc since it depends on heating,although it's normally for ac use (with ac any arc can only persist until the voltage goes through zero).
  8. sangesf

    sangesf Banned

    I don't know enough about AC breakers to say either. (the other thing, i need something that I can mount outside of my battery box and also is weather resistant)
  9. loquin

    loquin Active Member

    As long as the switch is rated to switch at LEAST 24 volts DC, at your rated current (15A), it would be fine. A switch which is rated at 15 amps will work fine at any amperage up to that point. You wouldn't need to get it oversized.

    The only time that the current would EVER be that high is if the dc-dc converter output was at max current. Your operational load is going to be in the less-than 100 watts range.

    As others have said, add a 15 Amp slow-blow fuse (or breaker) to the feed circuit. A slow-blow fuse handles short-term surge currents that you can experience when the converter starts up without blowing. That way, if you developed a short, the fuse would blow, the feed circuit would be disconnected, and nothing would fry.

    And, as far as switch ratings go, that's the current that they are tested to handle correctly over thousands of on-off cycles. In an emergency, they can handle more current that that. (at higher than rated currents, switches can experience 'erosion' of the contact faces. One or twice at double the current shouldn't destroy the switch - but, it will shorten its life somewhat. If you repeatedly exceed the current rating, it would lead to a short switch life, though)
    Last edited: Feb 14, 2009
  10. duivendyk

    duivendyk Guest

    I looked around on the web, 24V dc switches, rated at 30 A are not hard to come by,used in RV's etc
  11. sangesf

    sangesf Banned

    All fine and good, however, the switch is not going on a 15a line... It's going on a 30a+ line. I already have a switch after the DC-DC converter for the 12v stuff, it's the 24v 30a line going to the controller that I need a switch for.

    The REAL problem I'm having is finding ANYWHERE that has any kind of selection of 24v switches. (I want a switch to turn on/off, not a relay.)
  12. SirJakesus

    SirJakesus Guest

    I think the switch only has to handle the amperes going through it. If your DC-DC converter only draws 15 or less Amps you can use a 15A switch. You would only need a larger switch if for some reason you wanted to add a switch in between your battery and motor controller. It shouldn't matter if your batteries can supply 40a as long as that amperage isn't traveling through the circuit with the switch on it.
  13. sangesf

    sangesf Banned

    But wouldn't the amperage be pulled through the switch (between the controller and the battery) while I'm riding the bike?

    More on that in a minute, but first...
    Why does everyone want to talk about the DC-DC converter? Has NOTHING to do with it!

    I must not be explaining it correctly.....

    This has NOTHING to do with the Converter. I want a switch that is between the Battery and the controller.

    I have it set up like this....

    Battery with two sets of power (+ and -) wires... first set goes to controller, second set goes to the DC-DC converter, after the DC-DC converter is a switch, to switch off the 12v accessories (when I'm inside a store or otherwise not home, nor riding the bike, or when I'm charging the battery) so the converter part is fine.

    I want a 24v 30a switch between the battery and the controller. I want it illuminated. The same wires that supply power to the controller, are the same wires I (have to) use to charge the battery. I want to add a THIRD set of wires (to the two that are already there) and add a charger port, but I want the switch (in between the battery and the controller) to disconnect the controller when I go to charge the Battery. (and since it just happens to be there, disconnect the converter, but it's NOT necessary, so please no more suggestions about the damb DC-DC converter :))

    Now another question(s) come into play...
    What size (awg) wires should I have going from the battery to the switch, from the switch to the controller and from the controller to the 12v accessories.
    And for the "more on that in a minute part"....
    The other question is, if my bike is running, and I have a switch there (in the ON/Closed position) does the amp rating on the switch have ANY effect or disadvantage for the amps the controller will be pulling? My motor (on my 200lb+ bike) is a 250watt 24v motor, the battery is a 24v 30ah battery and is capable of 40a continuous / 60a peak draw, but I doubt the controller pulls any more than 30a from that low wattage/voltage motor. (I don't know what the controller pulls or is able to pull, but I was guessing that it would be somewhere close to (given the motor's rating) about 15a continuous and 25a max, hence for the desire to have an Illuminated 24v 30a Rocker On/Off Switch.) Anyone know where I can find one?
  14. duivendyk

    duivendyk Guest

    If you look around long enough at Amazon.com,you can find a 24V, 30A.dc switch,I did.It did take some digging,their categories are kind of screwed up.I'm not sure if it was illuminated.
  15. sangesf

    sangesf Banned

    If you found it on Amazon, could you look through your browser history and see if you can find it again and then send me the link?
  16. duivendyk

    duivendyk Guest

    I'll try tomorrow,& let you know,it was rather convoluted,I got there in Amazon,via a link from Google.But when you tried A directly it was pretty hard to find,I remember now.
  17. duivendyk

    duivendyk Guest

    I have looked around some more and have found a site that should be right up your alley.You can get to it via Amazon "home improvement"(hard),and I don't know if they sell all their stuff via A.You'd be probably better off going to their site directly:
    www.delcity.net and look under their product categories for "switches" ,then look for battery&ignition switches.I think you should also look under circuit breakers,some can be disconnected, like your house panel breakers.I think a breaker is nice to have in order to keep from overloading your controller/motor.BTW their search engine stinks.Good luck
    Last edited by a moderator: Feb 17, 2009
  18. sangesf

    sangesf Banned

    Thank you for the website and your time. However, they don't have rocker switches that are rated for 24v 30a or higher, actually they don't even have anything rated over 15a. :(

    I think I'm just going to give up on this. NO ONE makes a rocker switch (illuminated or not) that is rated for 24v DC 30a or higher. :(

    I think I'm just going to go with a "Battery Switch". I'm going to have to just give up on the illuminated switch idea and go with something more practical.

    Oh well.
  19. cooltoy

    cooltoy Member

    You could also try Marine places, I know for sure that they sell 24 volt switches for the bilge pumps.
    Also Golf carts use a small box to reduce the volts to 12, try ebay or golf cart sites
    Last edited: Feb 21, 2009
  20. sangesf

    sangesf Banned

    That are 8 in or more in diameter.