Blue shark amperage question

[LED4LYF]

I know the blue shark has a max 4amp input current. How would you figure out your input current? Does it depend on your batteries?

Also If I were to run 6 li-ion fully charged that would put the voltage at 25.2V, the blue shark input only says 25V ,would that little bit extra be a problem?

 

[arek98]

I believe that officaly 6 Li-Ions is to much for shark.

Input current will depend on battery and Vf of LED's. Shark is boost, it means that Vin is lower than Vled, this means that Iin is higher than Iled. To be safe lets assume 80% shark efficiency. Then Vin*Iin*0.8=Vled*Iled, given Iled max = 1A and Iin max 4A we have Vin min = Vled / 3.2. It means that if you go lower with input voltage then you will exceed max input current.

Let say you like to drive 4 XP-G in series, assume Vf = 3.5V @ 1A, so 14V Vled. If you use power source with less than 14/3.2=4.375V then you will need more than 4A current on input. This is simplification because we assumed 80% shark efficiency, it is much higher for small differnece between Vled and Vin and much lower for big difference (like 14Vled and 4.375 Vin) but this is general idea.

If you plan one level then it this is simple, but for multilevels you need to take into account that Vf of leds will be lower. It means that you should try to stay close to Vled with Vin for efficiency but it needs to be lower than Vleds on low level to stay in regulation, otherwise shark will go direct drive and you will loose low levels.

 

[LED4LYF]

I am running 7 xpg r5 with shark set at 1amp and using 4 aw 18650 in series for a 16.8v power supply.

I hooked my meter in line between the power of batter pack and the switch when I turn on my flashlight my amperage reading is 1.4 amps. I want to make sure that I am getting the most out of my set up. I am not sure if that is a good reading or not?

 

[Justin Case]

The 4A switch current limit is a typical value from the switcher IC datasheet. To be conservative, however, you might want to be conservative and use the 3A min value.

Regardless, if you are pushing anything close to 3A, you will probably have some serious thermal management issues if youe application is a handheld flashlight unless you have a massive heat sink.

To determine if your measured battery current draw is reasonable, you need to know what your drive current is and your Vbatt under load.

4xAW18650 won't hold 4.2V per cell under load. 3.8V or 3.9V would probably be closer to the actual voltage under load at the start.

Efficiency is probably around 85% for the boost ratio you face.


Use the following eqn:

Driver efficiency*power in = power out

Thus 0.85*Vbatt*Ibatt=totalVf*drive current

Total Vf could be around 7*3.4V. Vbatt ~15.6V. Drive current is 980mA nominal but I've measured 930mA and 950mA in two Blue Shark samples. Other CPFers have measured even lower drive current.

Solve for Ibatt.

Did you test your driver as described in the Shoppe's Shark thread. Is your trim pot at max?

 

[LED4LYF]

I used that equation with the theoretical numbers and I ended up with 1.7A. Mine was 1.4A so I guess the numbers are a little off or I have a little more resestance.

 

[Justin Case]

It does seem that your tail current is low, assuming that your trim pot is max'ed out.

However, to be certain, you need to measure your drive current and your Vf at that drive current. You can estimate Vbatt from the various discharge graphs on CPF for the tail current magnitude you've measured.

Or you can parameterize Vbatt by assuming a low and a high value (e.g., 3.7V and 4.2V) and calculating for Ibatt.

I have a 7 LED setup with a total Vf of about 22.4V and a drive current of 810mA (purposely set to that value). For 3xLi-ion, I measured a tail current of about 1.8A.

For the same setup but 4xLi-ion at 4*3.9V, I calculate an Ibatt ~1.4A.

Check your trim pot.

 

[LED4LYF]

I can't check it till monday but the pot on the blue shark was cranked all the way up. When I check the pot do I just set my meter in line on the positive output to the leds on the blue shark?

 

[Justin Case]

Re: your original question about using 6xLi-ion to provide 25.2V input, the datasheet says that 25V is the absolute recommended max for the boost IC. Granted, you will apply the full 25.2V only for a brief instant as the cells sag to the quasi-steady state voltage under load.

If you have a specific host that uses 6 Li-ions, then I'd probably charge the cells up to 4.10V each to be on the safe side.

Re: the trim pot, if it is set to the max resistance, then in theory you should get much more than ~800mA drive current. I'd put a DMM on the trim pot to verify that its total resistance is about 20Kohms.

The Shark uses a voltage divider circuit (via the trim pot and R6 IIRC) to control the drive current level. R6 should be a 20K resistor. Check that also.

Max drive current occurs when the control voltage is about 0.7V, which is when the trim pot wiper resistance is at least 20K (the wiper is connected to the control pin of the boost IC). Lower wiper resistance gives lower drive current. You can check that indirectly by turning the trim pot adjustement ccl IIRC to cut back the drive current, and measuring the resistance at the wiper. It should have decreased, giving you the decreased drive current.

You can indirectly estimate the drive current by measuring R6 and the trim pot resistances between the legs. The control reference voltage is 1.235V. Thus, the resistances need to be in the right ratio to give ~0.7V to the control pin of the boost IC for max drive current.

I think the drive current varies between its min of ~100mA at ~100mohms to ~1000mA at ~700mohms.

 

[LED4LYF]

I checked R6 and the pot, R6 only appeared to be 16k. I was not sure whick pins to measure on the pot so I did all possibilities and the most I ever got was 16k also. But I did hook my meter inline with the output to the leds and i got 960ma. So I guess I don't know what is really going on.

 

[Justin Case]

As long as R6 and the total trim pot resistance are the same, you should be able to get max drive current when the trim pot is max'ed out. IMO, 960mA is a reasonable value for the drive current.

If you are now measuring ~1A drive, then does that mean the driver is now working properly and the Osram is lighting up brightly?

 

[LED4LYF]

Yes the trim pot and r6 were measuring very similar.

The 7 xp-g array always worked beautifully I just wanted to make sure that I was getting my full 1 amp out of my system. So if I measured 960ma with my fluke DMM that means I am pretty close to max current correct and as bright as I am going to get with the blue skark?

What does osram mean? I am not sure what you mean?

 

[Justin Case]

Sorry, that was a case of neural crosstalk. I got mixed up between your Blue Shark issue and vestureofblood's. He is the one wiring the Blue Shark to a 6-die Osram.

Your Shark is doing fine at 960mA drive. Out of curiosity, what total Vf do you get with the seven XP-Gs at 960mA drive?

 

[LED4LYF]

Sorry have not taken that reading, I tried and like an idiot I shorted one of the led and it went poof. So I am down one led. Each of my leds are mounted on a 10mm mcpcb board. Any chance you know where to get another besides cutter? I don't want to pay 12 dollars shipping for one xp-g.

 

[Justin Case]

Where are you located? I have some XP-G R5s on 10mm boards. What tint did you get from Cutter? I bought mine before Cree offered tint choices, but they seem reasonably white. The R4s that I had were definitely greenish-tinged.

 

[LED4LYF]

I am not sure I bought mine from cutter right when they had the option for R5 bin. There is two choices now and I am not sure which one I ordered.

Here are the two numbers on cutters website

XPGWHT-L1-1B0-R5-0-01
XPGWHT-L1-0D0-R5-0-01

I am thinking I got the first number (1B0 )because the second number (0D0) seems to have just changed in the last few days it used to be like a 1C0, now that option on cutters website is not even there.

Do you know which of the two came first?

Do you know which of the two you bought?

I would definetely be interested in some of your R5 if they are the same.

Do you have the round or square board?

 

[Justin Case]

As I wrote before, I bought my XP-G R5s before specific tints were available. These are on 10mm rounds.

The order code for the XP-Gs that I bought is XPGWHT-L1-0000-00H51 R5. Kit 00H51 encompasses the following tint bins (it is my understanding that when I made my order, what tint you actually received from of this tint range was a lottery):

0A, 0B, 0C, 0D, 0R, 0S, 0T, 0U, 1A, 1B, 1C, 1D, 1R, 1S, 1T, 1U, 2A, 2B, 2C, 2D, 2R, 2S, 2T, 2U, 3A, 3B, 3R, 3​

 

[LED4LYF]

Cool I will look at my order and see If I had the same number

 

[LED4LYF]

Could not find the number yet, I am not sure where to look. I forgot to ask you, what date did you order yours? On my invoice it says 02/23/2010, so if you ordered yours around the same time as I did I bet we both bought from around the same batch. If I can not find the number would you be willing to sell me some?

How many could you sell?

How much?

How do I pay you? Do you have pay pal? If so what is the adress and I will send you payment If I can not find what tint color mine are.

 

[Justin Case]

Could not find the number yet, I am not sure where to look. I forgot to ask you, what date did you order yours? On my invoice it says 02/23/2010, so if you ordered yours around the same time as I did I bet we both bought from around the same batch. If I can not find the number would you be willing to sell me some?

How many could you sell?

How much?

How do I pay you? Do you have pay pal? If so what is the adress and I will send you payment If I can not find what tint color mine are.

I'll have to check my purchase date. I'll PM you with answers to your other Qs.