5V USB charger for 6V electrical systems

[nrcb125]

I think an LDO voltage regulator with a sufficient amp rating to match the USB standard (900ma) and an output voltage of 5V should do the trick. Hook up Vin to the battery positive using a relay and a handlebar switch for the relay, GND to battery GND. Then cut a USB cable, use the red and black wires to connect to Vout and GND respectively. Wham bam USB charger on a bike with a 6V electrical system.

My main concern is the the generator putting out power which isn't smoothed and the voltage regulator not being able to handle this well. The battery should smooth the input from the generator right?

Thoughts? Comments? Critiques?

 

[jay_kent]

I'd run a small capacitor on there to help with any voltage drop and smooth it out even more.

 

[mydlyfkryzis]

6 Volt battery is actually 6.3-6.4v. To charge the battery, the system needs to put out 7-8 volts DC. That seems a bit to put in a USB connector.

Buy a 5 volt voltage regulator. Some of the e-bay places have 3 for a dollar shipped. (I got 2 7809's -9-volt) for a buck.
Get 7805 type. Something like this:

http://www.ebay.com/itm/3-x-L7805-7805-Voltage-Regulator-5V-1-5A-SGS-THOMSON-Free-Shipping-/220929958025?pt=LH_DefaultDomain_0&hash=item337073a089

A small cap and the regulator will take 6-24 Volt DC supply and make it a regulated 5 volt. Still cheap, but a lot easier on the USB electronics.

Just allow a few weeks for delivery from Thailand.

 

[nrcb125]

I'd run a small capacitor on there to help with any voltage drop and smooth it out even more.

Will do!

6 Volt battery is actually 6.3-6.4v. To charge the battery, the system needs to put out 7-8 volts DC. That seems a bit to put in a USB connector.

Buy a 5 volt voltage regulator. Some of the e-bay places have 3 for a dollar shipped. (I got 2 7809's -9-volt) for a buck.
Get 7805 type. Something like this:

http://www.ebay.com/itm/3-x-L7805-7805-Voltage-Regulator-5V-1-5A-SGS-THOMSON-Free-Shipping-/220929958025?pt=LH_DefaultDomain_0&hash=item337073a089

A small cap and the regulator will take 6-24 Volt DC supply and make it a regulated 5 volt. Still cheap, but a lot easier on the USB electronics.

Just allow a few weeks for delivery from Thailand.

An LDO voltage regulator has a dropout voltage of less than 2V. The L7805 chips do not. Their dropout voltage is 2V so the system would have to maintain >7V to keep the regulator pumping out 5V. Something with a low dropout voltage would more reliably put out 5V should the system voltage drop below 7V. The other issue with the 7805 series is their packaging. They do not have an MSL 1 rating. This means they won't reliably operate in unideal moisture conditions like those found while riding past a certain amount of time.

The criteria I've compiled so far:
-5V fixed output
-1A output rating
-<0.5V dropout voltage
-MSL 1 rating
-capacitor on the output pin

This regulator seems to meet all of them except the 1A rating: http://www.newark.com/linear-technology/lt1129ist-5-pbf/ic-ldo-volt-reg-5v-0-7a-sot-223/dp/57M2106?in_merch=Popular%20Products

However it seems voltage regulators in parallel are okay to effectively double the current output. The only downside to this regulator is the cost, ~$5 per chip.

 

[mydlyfkryzis]

I missed the LDO part in the first sentence somehow. I was first under the impression that you were hooking direct to the 6v battery.

You are absolutely right. The LDO Regulator is the way to go...