Help ! Shark Driver/Twin Seoul P4s/ 7.2V supply . . . will it blow? ... any ideas?

In short the plan was to use 7.2V batteries( NiMH initially ) to power 2 Seoul P4's through a shark driver. all the bits are ordered now, so little going back. :thumbsup:

i had originally provisioned that 2 leds would be about 8V and that 7.2V and falling under use from the battery would be a suitable source.

but i've since gone back over the finer details to see that the Seoul's are 3.25 volts ... as i understand it, this would mean the supply is greater than Vfout and the LEDs would blow. :sigh:

But i dont want to swap to a buckpuck driver as i would still be needing to cover the 2V overhead ontop of the 6.5V of the LEDs, which i dont have from a 7.2V battery

It has to be pairs due to the enclosure.

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So, am I right in saying that the 7.2V supply would blow the circuit? :thumbsdow

If so, would it be possible to pre-regulate the 7.2V down to 5V and then run the shark off the regulated voltage? :thinking:

Am I right in saying that if the LED string is run at a max of 1000mA, then the supply current is going to be slightly higher? If so, by how much?

I could fit in a 5V regulator with a 5A capacity between the battery and the shark. Would that be enough to handle the shark?


I would really like to persevere with the 7.2V NiMH route as it would make for an easy swap further down the line to LiPo batteries too.

many thanks in advance.

Donald

As was passed on to me by another member.... Try HERE.
Adjustable output regulators. Kinda pricey, but small and off the shelf. Don't forget the vf of those SSC LEDs will drop even more when dimming. A quick glance at the spec sheet will show how much at very low currents.

I have a spare DB1000 that I would be willing to swap for your Shark. PM me if you are interested in trading.

If it fits, you could also run 3 Seouls at that voltage for more light. Don't forget that NiMH batteries could be 1.4v hot off the charger.

Charts form White LED Lumen Testing.

jtr1962 said:

Seoul Semiconductor W42180 bin U (tested February 2007)

Click to expand...

From Cree Q4 evaluation

evan9162 said:

Technical evaluation - Cree XR-E Q4 bin

Click to expand...

I hope that charts and graphs help.

Welcome to CPF!

If you only plan on driving them at 1A and not dim it down you should be fine.

My only concern is what your battery pack really is fully charged. Is that 5 cells in the battery pack? Fully charged NiMH is around 1.4V/cell or 7V which would be a better situation than if there are 6 cells in the pack and fully charged would then be 8.4V.

At 1A drive current the Vf will be in the range of 3.5V or if you are lucky a bit higher. Usually, you'd want the lowest Vf possible, but, in this case you'd like one that when two are stacked together are equal to or less than the full charge state of the battery.

Also, take into consideration that the battery under load could sag a bit and that might help out in this situation.

Wayne

Thanks guys - especially for the charts. Really very useful.

When I said the NiMH route, reading back i wasn't specific about it. I was planning on using the 7.2V radio control car style batteries that you would buy complete with a tamiya connector on them. Easily available, and in the future, i can make the change to LiPo ones if i wanted. When i think about it, its a pack of 6 cells, 2 pairs of 3 in parallel iirc. I'll need to fully charge one and really see just exactly what voltage its pumping out.

I cant run 3 emitters in series as the housing isn't big enough. The front section has a space of 43mm wide, 20mm high. It really can only fit 2 in there side by side.

I also really do want the dimming ability too. I dont need full brightness all the time, its planned to be a commuter bike like so having it varying between being seen and see-by is useful.



So by the sounds of it, a voltage regulator is a viable proposition. Thanks for the link Havand, but as i understand it, a single 1A regulator wont be enough, i'll need to get a 3A or 5A unit. These regulators drop about 1.3V across them to work properly, so for 5V output, i'll need 6.3V supply or better. This seems to fit better into the envelope of available voltages.

Ho hum . . . another order of bits ! Its going to get tight inside the little box!

Thanks chaps ... as soon as the bits arrive, i'll be taking lots of pictures.:thumbsup: