Actual 1157 bulb amp draw

[eVaDeR85]

Ok ive been doing some research and found this thread...

http://forums.radiocontrolzone.com/showthread.php?t=188912&highlight=bulb+discharger

where someone says that when both filaments of the normal automotive 1157 bulb are connected the total amp draw is 2.1 and .6 for the the two filaments which is 2.7 amps total for one bulb. Here is a real kicker. For 2 years now ive had 10 1157 bulbs connected in parallel to dishcarge my batteries. Never did any calculations till now on it but ive figured it up and the 2.7a number is I believe to be the actual avg amp draw of these bulbs at 7.2 volts. So here's my scientific observations....

I have a rather old but still in healthy condition 1900mah NiCD pack that is only 1 and half years old. My old 10 bulb discharger is now a 9 bulb both of the filaments in one of the bulbs have burned out. I just charged my 1900 pack which was not fully discharged and took 22 minutes at 4 amps. Comes out to around 1466 mah. Ok I discharged the pack and bulbs began to dim after 4 minutes 30 seconds approx. This pack hasnt been cycled in quite some time. Figuring up the amp draw for 2 amps per bulb (18a total). My calculations show that my battery was only successful in delivering about 1300 mah of current...really sad and scared me to be honest as its my only pack as of now. Ok after doing some research and plugging in the numbers for the 2.7a draw (24.3 amps total) my calculations showed a little over 1800 mah.

Again these batteries havent been cycled in awhile which shows more accurately in the 2.7 amp bulb draw scenario whereas the 2 amp bulb draw scenario would suggest a dead or dying battery. But these batteries still have plenty of punch in them...even with my SS5800 brushless motor!

So I ask you people of the RC world, which do you believe to be true? I myself believe that the actual draw of the bulbs are 2.7 amps. And for those skeptics out there.... YES I know this is not very precise but the math just works out better under the 2.7 amps per bulb that was suggested in the thread above. Anyone care to comment? :teacher:

[loopy]

Hi

You cant assume 7.2v from the battery because it discharges in a curve.
When it is freshly charged it will be sitting at around 8.5-9.0V. A this point it will discharge at a higher rate than later in the cycle.

Some of the power from the battery will have disappeared as heat as a result of its internal resistance.
You can use your method to compare your batteries performance over a period of time but the numbers you are getting are not necessarily real world figures.
You could chart your batteries discharge average V with a watch and voltmeter to get a more accurate idea though it would be easier to ask someone with a charger with a discharge feature to discharge it for you and get the figures off their charger.

The best guage of your batteries performance is how it runs on the track or wherever you normally run it.

[awnelson]

Amperage draw = Resistance X Voltage

The ratings on those bulbs assumes an alternator charging at a regulated 14.4 VDC. As your voltage drops on your discharger, the amperage draw drops relative.

[eVaDeR85]

I knew someone would argue that point. And yes I know as voltage drops so does the current. And as I stated I knew it was very accurate but I figured it would be close enough. Im going to do some more research on this subject. I might even swipe a DC ammeter somewhere to test my theory. Im not going to let this rest because its sparked my interest.

[kschauwe]

I had measure one at 2.2a on a six cell pak.

[bdebde]

I had measure one at 2.2a on a six cell pak.

I got the same here.

[Grant Tokumi]

I knew someone would argue that point. And yes I know as voltage drops so does the current. And as I stated I knew it was very accurate but I figured it would be close enough. Im going to do some more research on this subject. I might even swipe a DC ammeter somewhere to test my theory. Im not going to let this rest because its sparked my interest.
If you are really interested, grab one of these whattmeters.
http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LX3605&P=ML
Its a bit pricey ($50) for education, but I could argue that I retained much more knowledge from this $50 whattmeter over a $80 textbook. There are different brands out there and I thought Astroflight offered this particular one with alligator clips or dean ultra plugs.

Anyways, I have one of these and it is really a good tool to find exactly what you are looking for. It measures the amps which is what you are looking for, but it also simultaneously measures the voltage which can tell you what kind of voltage drop you are getting when you plug in the discharger. Terms like "voltage sag" really start to make intuitive sense from watching the meter and the bulbs after you plug it in. And finally it give the mah that was sucked out of the battery during the duration. All nice information to give you firsthand knowledge on your battery characteristics.

Nowdays, I plug it into my 12 volts devices like a flourescent light, so I can check the mah draw at the end of the evening race to get a rough idea of how much of my 12v gel cell got used up during a race due to my light. Its a handy toy. :)

[Grant Tokumi]

I'm digressing now, but I also just ordered couple of these last night:
http://meritline.stores.yahoo.net/kilwateldet.html
Its kind of like of like a whattmeter, but for your house. I can test things around my house to help get firsthand knowledge on how much electrocity my home electronics uses. I hope to be able to save some $$ on my monthly electricity bill. Its along the same lines as the whattmeter, so its related in my book. :)