Li-Po batteries for DIY HID?

[omnikron]

Hi,
i'm a long time lurker in these forums and something finally prompted me to ask a question in this forum.

i custom made a cheap light with a automotive 35W HID, and a 12v 7.5AH SLA battery.

the runtime is about 70-80 minutes, which is great apart from the weight. the 7.5AH battery is just too heavy for me.

So my questions are :
1 )i looked around and the next best solution is Lithium rechargeable, i opted for Li-Po 11.1 packs which is closer to 12V, or should i go for the 14.7v packs?

2)at my area, the highest mAh for a 11.1V that i can buy is the 4500mAh / 4.5AH how is the runtime affected, will it affect my runtime by half? or the better efficiency of the Li-Po packs work just as good if not better than a 7.5AH SLA battery.

3) should i invest into a balanced charger? a good one cost about USD100.00 which is substantial at my part of the world.

just as a comparison, a 12v 7.5AH SLA cost me USD25+ while a 11.1V Li-Po 4500mAh cost USD98.00. a Li-Po pack cost 3 times a normal SLA battery. as a student on a budget, i just don't have the funds to "try". so i am hoping experieced people can enlighten me.

i'm very sorry to ask such simple questions but i couldn't find any accurate info at the batteries section, because i am using it on a HID light, i hope i can get better answers at this section.

 

[yo6ial]

Hi omnikron!

Most important: What are the specs on you're HID drivers?
Do they cut-off at under-voltage?
Firstly I'd say to go for the 14.4V (14.7?) pack as you get more watts available.
And the drivers will not be happy on lower voltages as they would have to work harder to keep the bulb lit.

Think in watts to make an idea about run time.
On a 14.4V 4.5ah you get a pretty good 64.8Watts, relating to a hefty 1 hour and 45 minutes of life. (maybe 2 hours)
The lead battery offered so little time mainly because of it's poor behavior on high loads. Regardless of the 90watts held in it, the very low performance made about half of that power to go up as heat inside the cells...

I'd use a balanced charger for my li-ions. If i had one :laughing: ...
Until now, my bike lights, using the 4.4Ah 14.4V Li-ion pack are still operational, and for the last two years of use, the pack remained balanced and hold up all the rated power without using a smart charger. (actually i use a "smart" charger: a constant current psu along my digital multimeter, and a constant watch thrum the charging process)

Greets!

 

[omnikron]

Ah, great.

1) the kit does cut off at about 7 volts.

2) the closest Li-Po pack is 14.8V, would that risk blowing the ballast? as i have not tried it on such a high voltage before. 13V yes but not 14.8. i believe automotive HIDs are rated at bout 14.4v or can they tolerate higher volts before they are damaged.

3) so Li-Po batteries, even at lower mAh, can perform better than SLA batteries under high load?

and finally, how many C should i look at? 15C? 20C? the initial burst is 10+ amps stabilizing to about 3.5 3.6amps.

 

[yo6ial]

On an motor vehicle, the 12V line can peak over 16V on high throttle (ok, the avarage car will not do this) , so don't worry bout it.
The driver will like better the higher voltage because it will draw less current for the same amount of power.
Consider using a protection circuit for the pack, if the cut-off is arownd 7V. Don't discharge you're pack below 2.8V per cell. Or, better yet, use protected cells.

At start, 10Ah means just about 2C...
2C 5.1C or xC means just "x times nominal capacity" For those few seconds the pack will behave right... if not, the protection will kick in.
A big capacitor, between 10000uF and 100000uF should buffer the driver's hunger at startup.
Use fuses! Thermal ones and electrical ones, just as a precaution.
Cheers.

 

[BVH]

I know you have budget limitations but by the time you buy a Lithium pack and some type of balancer, you will have spent more than just buying a very high ampacity Li-Po pack with a balancing, over charge, over discharge, over current circuit board shrinkwrapped right into the pack. I used a Batteryspace dot com 14.4, 6.4 Amp Li-Po for my Blitz HID mod and get 55 minutes running a 114 Watt ballast. The little PC board gives you all the protection you need. Of course, definitely use fuses.

 

[Richie086]

I used a Batterystation dot com 14.4, 6.4 Amp Li-Po for my Blitz HID mod and get 55 minutes running a 114 Watt ballast. The little PC board gives you all the protection you need. Of course, definitely use fuses.

Any links to the actual page and product would be great. I'm considering upgrading one of my POB's to Li-Po. I'd have to see it there would be room inside for everything. But this PC board sounds great.

 

[BVH]

I'm not sure if we can direct link any more. Opps, I was wayyyyy off. Wrong vendor.

Batteryspace dot com /index.asp?PageAction=VIEWPROD&ProdID=4032

 

[jordananders]

i custom made a cheap light with a automotive 35W HID, and a 12v 7.5AH SLA battery.

I want to do the same thing (Use a HID headlight in a flashlight) but I can not find a driver/ballast small enough. What did you use?