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Old October 9th, 2007, 02:14 AM   #1
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NRG Varalux battery discharge question

Hi all,

I recently purchased a used NRG Varalux with a 100 watt bulb and 95 watt/hour battery pack. Assuming the battery has a good charge, the light is turned up all the way, how long should the battery last before discharging? I was assuming about 50 minutes but my unit shuts off after 30 minutes, seeming to indicate the battery pack is nearing the end of the life...

I'll give the battery belt another try but I'm having my doubts - should I consider returnig the unit to the eBay seller?

Thanks, Michael
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Old October 9th, 2007, 11:17 AM   #2
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Most likely, everything's fine. A battery won't run your light at full power, then suddenly drop dead at the rated capacity/life. If you calculate your battery's capacity, you would think that the 100 watt light would operate for 57 minutes. Reality is that after (my guess here) 30 to 40 minutes, your light will likely dim or go out altogether. If you need the light to be "ON", and at the full 100 watts for a longer period, you'll need a larger battery belt. I use a Bescor PRB-24 to power my Varalux Pro. The manufacturer states on their web site that it's good for 2.4 hours at 100 watts. If you do the same math that I did above, you'll calculate a run time of 2.88 hours. I can't say what reality is in this case, because I've never needed 100 watts for more than a few minutes.

Which brings me to another thought. Do you really need 100 watts for more than a few minutes? I can only imagine that would be the case on a large shoot, or in a studio. In either case, you can get power supplies to operate the Varalux, or get yourself some studio lights.

Sorry to get long-winded, but I hope it's been helpful.

Cheers!

Mark

Oh, if you got that set-up at a good price, I'd keep it.
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Last edited by Mark Holland; October 9th, 2007 at 11:18 AM. Reason: Addendum
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Old October 9th, 2007, 12:33 PM   #3
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Thanks Mark,

I appreciate your info on the Bescor unit. I looked at the specs on your battery - it's 12 volts, 24 Amp hours, Runs 5 Hours @ 50 Watts, with 26 Hour Charge Time. So at 12v x 24A, I agree with your 2.5 hour assessment. In response to your question, no, I'd never be running my NRG wide open until it failed. The whole purpose was to validate the ability of the battery belt to hold a charge (nothing worse then getting embarrassed on an important job). I can't think of another way to dynamically determine the ability to hold a short-term charge; if you have a better test, please let me know the test procedure.

I also asked a colleague who recommended the NRG for his opinion on my battery question - here's his response:

*** It sounds like the belt is either very used or has been abused. We use the 880 and it last longer than an hour so your 970 would last even longer. I have had good luck with buying used NRG lights, but not much luck on used belts. We both use the 880 belts. You gotta love the 5 lb. belt. You don't even know it's on versus when I used the 970. Those extra pounds really add up.

Mark, back to the specs on your battery. I noted that the charge time was 26 hours - no way did I charge that long before conducting my test. I don't have the specs on the NRG belt so I'll definitely give it a full day of charge before I try a second test - I'll let y'all know the results.

Warm Regards,

Michael
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Old October 9th, 2007, 02:09 PM   #4
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As far as used belts go, if it's in physically good condition AND the price is right, I'll buy them, rebuild the electricals, and it'll be as good as new for far less money!

I don't use NRG belts, so the model numbers you refer to are meaningless to me. I assume one is bigger (physically and electrically) than the other?

Be careful testing your battery belt. It's really not the best thing for the battery to be fully discharged. If you've got a local "Batteries Plus", someone there should be able to do a load test on your battery belt, and if you need a new cell, they can help you with the installation.

Like I said before, if the price was right, I wouldn't send it back. The MOST you might need is a new cell in the belt pack.

BTW, you mentioned "getting embarrassed on an important job". That's one reason I always keep a spare lamp, and a spare battery belt close by.

Cheers!

Mark
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Last edited by Mark Holland; October 9th, 2007 at 02:10 PM. Reason: Spelling
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Old October 10th, 2007, 08:34 AM   #5
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Michael, when a battery is rated for capacity, usually the manufacturer loads the battery at 1/10 or 1/20 it's C rate. A "C" is the number in AH rating. In your case your belt is probably 8AH (I assume it is a 12V belt), so C = 8A.
When a belt is tested at .8A-1A, it is very easy for it to deliver it's full rated capacity. When the same battery belt is loaded at 1C rate (your 100W light) probably uses 8A, it is really working very hard, wasting much of it's charge on internal heating. It's capacity as delivered would be much less than if loaded at 1/10C, around 50%-60% of nominal. So your results are pretty much in line with what is expected. If you really want to run a 100W light for longer times, you need to use a larger capacity battery belt, so your current draw will be easier on the battery.
As far as charging time, I think you use a Ni-Cad battery belt by NRG. They can be recharged very quickly, 2-3 hours if you have a fast charger for it. The belt mentioned by Mark is Bescor make. They do not make Ni-Cad belts, only Lead Acid. The Lead Acids are less expensive than Ni-Cads, but they do not take fast charge, only long overnight charge due to chemistry. So do not compare charge times between the two. Apples and oranges.
HTH
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Old October 10th, 2007, 01:56 PM   #6
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NRG Battery Belt - Going, going, ...

Hi Alex,

Thank you for the interesting post. I agree with your assertion of C ratings, however in my actual test the batteries were cool the entire 30 minute period. I also agree with your comments regarding the variance in charge times between Ni-Cad and Lead acid (I didn't realize the Bescor was the later). At any rate, regarding my actual NRB batteries, here's an excerpt from a recent EMAIL I received:

*** It sounds like the belt is either very used or has been abused. We use the 880 and it last longer than an hour so your 970 would last even longer. I have had good luck with buying used NRG lights, but not much luck on used belts. We both use the 880 belts. You gotta love the 5 lb. belt. You don't even know it's on versus when I used the 970. Those extra pounds really add up.

So if my battery was indeed charged after a few hours but has a life significantly less than a smaller pack, I'm more convinced the cells are nearing the end of their life (confirmed by the above EMAIL regarding their experiences with used NRG batteries). Fortunately, the eBay seller gives great service and stands behind their products so I'm sure we can work this out.

Thanks to everyone for their advice and counsel.

Michael
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Old October 10th, 2007, 02:27 PM   #7
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Well, the message that you received stating that the 65WH belt delivered more than an hour, can not be possibly refering to the same light that you are using. It is technically impossible to power a 100w light for more than a hour usine a 65wh battery. He probably uses a 30W or 50W light. Do not get me wrong, I can not assure you that what you have is 100% good, just thought that before going through sending it back and getting a replacement, you will know what to expect from it :-)
Alex
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Old October 10th, 2007, 05:55 PM   #8
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Alex,

Yes, good point and obviously it's an apples to oranges comparison - I'd never suggest a 65 watt/hour battery would power a 100 watt light for more than an hour. So if the post came across that way and confused others, I apologize for the distortion.

The quote came from a leading videographer who was on a road trip and was giving me a quickie response with his impressions. So while indeed they use a 100 watt bulb, I'm sure when he and his wife are on a wedding shoot they aren't running the NRG at 100 watts continuously. Thus, his terse EMAIL made sense to me from a gut level, while we know the math doesn't add up as a direct comparison.

Thanks again for pointing this out.

Michael
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Old October 11th, 2007, 03:37 AM   #9
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Resurrected NRG battery belt

Hi all,

Okay, I have good news on my NRG batter belt (call off the dogs). After recharging the unit for 24+ hours, the pack ran for over 50 minutes before starting to dim. So apparently the NRG battery belt requires more than 8 hours to fully charge. I must say, the NRG unit throws a huge light - when I take it out at night while walking my dog, this baby throws as much light as an automobile headlight! (would definitely mesmorize the talent - "bambie in the headlights!...) Anyway, I'm happy to report the unit is working fine.

Thanks again y'all, Michael
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Old October 11th, 2007, 02:50 PM   #10
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Good for you! Glad to hear it!
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