Sturmey-Archer Dynahub

Discussion in 'Electrical' started by H20RIDER, Aug 18, 2012.

  1. H20RIDER

    H20RIDER New Member

    thread split off the HT 6v Charging System w ground thread.

    Okay...I am trying to figure out a variation on this system. I need to because I have a Sturmey Archer hub dynamo and a led headlights
    /taillights that are designed for the dynamo.
    HOWEVER, I also want to power a 6 v horn. I have a 6v rechargeable lantern battery (lead acid). Finally, I have a kill switch.
    So far dynamo is soley connected to the lights. The kill switch comes from the engine (I assume the "white wire ", yet it is not white. Neither the honr nor the battery are connected to anything yet. I have made a rectifier in case I can use the dynamo to charge the battery.
    So...what's the best way to set all this up?
    Possibly leave the dynamo to the lights?
    Charge the battery with the white wire?
    Could a big capacitor take the place of the battery if it is just for an occasionally used horn?
    If the battery is used, will this act as a kill switch?
    Best to just charge the battery at home and leave the white shire and dynamo alone? ( not my fav. option..... too simple.)
    Tie a cat to the handlebars and pull it's tail when I want a horn?
    Heck, I'm not even sure I have the right wire on the kill switch...but it does work.
    Thanks fo any help...especially very simple help.
    Last edited by a moderator: Aug 28, 2012

  2. H20RIDER

    H20RIDER New Member

    Okay...I found out that a capacitor won't would need to be way too big.
    Also, it is beginning to seem that charging the battery while riding, only or horn use, is a waste of effort. Seems better just to recharge between rides. The horn doesn't get used much anyway.
    Also, I came across a 114 db bike horn that uses a 9 volt battery. The hornet db114 . That, too, would simplify things...and is way louder than the 6v motorbike horn that I
    I've been fooling with.
    Que sera....
  3. loquin

    loquin Active Member

    For the S-A dynahub: Use a bridge rectifier, else you're wasting half your output. Since it is rated for 6 volts, you want to waste as little voltage as possible, so rather than using a single, standard silicon bridge diode, instead use 4, 2A Schotkey diodes to create your bridge. (They have a much lower forward voltage drop than standard silicon diodes and will therefore waste less of the available power.)

    If you have a 6 volt lead acid battery to charge, you should be able to get away without a regulator, but the battery life might be shortened a bit. If you're using 4 (or 5) NiMH (Nickle-Metal Hydride) batteries in series, they have charging characteristics that need to be followed. NiMh batteries, if 'speed' charged, must have their temperature monitored during the charge cycle. When the temperature of the battery begins to rise quickly, the charge MUST be stopped, else the battery will be damaged. On the other hand, if you 'trickle-charge' the battery, at about 1/10th their rated discharge current, they may be charged indefinitely. Since the circuitry to monitor battery temperatures can be complex, a trickle charge is probably the approach for most builders to use.

    I located a MiMH current limiting charge circuit here that I adapted for the S/A DynaHub, and the Cree R2 LED module that etacovda recommended here (and which I've used, and can also recommend.) The SR-260 Schottky diodes can be had through EBay for a decent price.

    After the circuit is built, insert a DC MA meter at the point referenced on the schematic, and adjust the charge current to 60 MA. This limits the trickle charge current to a value (1/10 rated output current) which will not damage the batteries. If your batteries have a higher capacity, or have a different rated maximum trickle charge current, adjust the maximum charge current to no more than the recommended value.

    As only 60 mA are used for charging, the remainder of the Dynahub output is used for lighting (through D5.) As you slow down and stop, the batteries 'take over' and feed the light through D6 until you start moving again, at which time, the trickle charging mode starts.

    Also, note that the cable from the Dynahub to the diodes must be floating (Neither side grounded.) Otherwise, you will lose half your available power.

    This 4-cell circuit provides 4.8 volts at the battery terminals, which is fine for the DealExtreme lighting module (and it allows charging at a lower supply voltage. If you absolutely must have 6 volts, you'll have to come up with a custom arrangement for the AA batteries, as they aren't standardly available in a 5 cell configuration. Since the supply voltage needs to reach the battery voltage + 1.2 volts, charging can't begin until the dynahub output reaches 7.2 volts in this case.

    Edit - Just noticed that the schematic doesn't have a value for the capacitor - it should be a 220 to 470 uF range, 25 volt electrolytic cap.

    NiMh Light Charger.jpg
    Last edited: Aug 28, 2012
    Dankoozy likes this.