From what I've read, the best cell to use in a ROP is one that can sustain a high current load, correct? Also, I've read that the CPB1650 is good, but no longer sold by cheapbatterypacks.com, and that a good alternative is the "Elite 1700," correct? My main question is: should I order just the 6 I need for my 2D ROP, or should I get one or two extras in case some are bad? Do these cells have a good reputation for being long lasting?
Best NiMH for ROP - Elite 1700?
- Thread starter copperfox
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mdocod
Flashaholic
The elites will do well, Sanyo eneloops also perform well in an ROP.
Just the Eneloops, or any precharged, low self-discharge NiMH cell? I can buy a 6 pack of the (new?) Duracell Precharged batteries at a local wallyworld for ~$17 which saves me $10 over the Elite 1700s... But I will only do that if they perform the same in the ROP.
I just want to be sure that whatever cells I buy can start on the first push of the switch and sustain the current needs of the ROP HI.
I just want to be sure that whatever cells I buy can start on the first push of the switch and sustain the current needs of the ROP HI.
mdocod
Flashaholic
you seem to be confusing issues of various battery chemistries. The issue of not being able to "fire up" a lamp on the "first click" is ONLY an issue that pertains to protected li-ion cells and has absolutely nothing to do with NIMH cells, you could slap the LOUSYEST AA NIMH cells in there and it WILL fire up on the first click every time, it just might not be as bright as it could be.
Eneloops are the only LSD cell I have seen that we have some actual test results for. Silverfox has some good looking graphs on these, showing respectable performance to 5+A. The other LSD cells might be great, but I have no way of knowing one way or another. So just recommending a cell that is verified as being a solid performer.
Cells like the Elite 1700 WILL outperform the eneloop in an application like the ROP, the Elite cells will drive the bulb harder. But it all depends how nuts you are about pushing it to the limit.
FYI: you can get an 8 pack eneloops at Circuit City for $20. (if the price inside is higher just ask them to give you the website price)
mdocod, thanks for clearing up the confusion regarding the start up issue...I must have gotten confused when I read threads about people wanting to put two 18650 li-ions in a c-cell mag to do a ROP. Thanks again.
I have no doubt that the Elite cells will push the bulb harder than LSD NiMH's because of their ability to provide high current, but the question is: How noticeable is this to the naked eye? Or more importantly, is there a sag in brightness for the first couple minutes using LSD cells instead of the Elites?
I have no doubt that the Elite cells will push the bulb harder than LSD NiMH's because of their ability to provide high current, but the question is: How noticeable is this to the naked eye? Or more importantly, is there a sag in brightness for the first couple minutes using LSD cells instead of the Elites?
SilverFox
Flashaholic
Hello Copperfox,
In high drain applications, it is always recommended to purchase extra cells and then to try to match your cells for the best performance in your application.
Keep in mind that the CBP 1650 mAh cells did not do all that well unless you used them immediately "hot off the charger." I have not checked the Elite cells, but the high current specs are hot off the charger specs. You can expect reduced performance if you charge the cells, then let them sit for awhile.
To get the best high current performance from cells like these, they are often charged at 2C, then used immediately. If they sit for 5 minutes or more after charging, they tend to loose some of their performance.
You may be able to search on CBP 1650 cells to see the difference between charging them up, letting them sit for 30 minutes, then using them, as opposed to using them hot off the charger.
Tom
In high drain applications, it is always recommended to purchase extra cells and then to try to match your cells for the best performance in your application.
Keep in mind that the CBP 1650 mAh cells did not do all that well unless you used them immediately "hot off the charger." I have not checked the Elite cells, but the high current specs are hot off the charger specs. You can expect reduced performance if you charge the cells, then let them sit for awhile.
To get the best high current performance from cells like these, they are often charged at 2C, then used immediately. If they sit for 5 minutes or more after charging, they tend to loose some of their performance.
You may be able to search on CBP 1650 cells to see the difference between charging them up, letting them sit for 30 minutes, then using them, as opposed to using them hot off the charger.
Tom
Carpenter
Enlightened
SilverFox,
So what would you recommend as the best battery for a ROP? I am currently using Titanium 2600's but if there is something better out there...
BTW - I am using a slow charger rated at 250mA / channel. I guess that rates mine at about .1C
Thanks
Mike
So what would you recommend as the best battery for a ROP? I am currently using Titanium 2600's but if there is something better out there...
BTW - I am using a slow charger rated at 250mA / channel. I guess that rates mine at about .1C
Thanks
Mike
SilverFox
Flashaholic
Hello Mike,
If you are going for run time, stick with what you have. If you are going for brightness, check out a set of the Elite cells. If you want something in the middle, go with the Eneloop cells.
In all cases, you will get marginally better performance if you charge at something like 1500 mA.
Tom
If you are going for run time, stick with what you have. If you are going for brightness, check out a set of the Elite cells. If you want something in the middle, go with the Eneloop cells.
In all cases, you will get marginally better performance if you charge at something like 1500 mA.
Tom
Nubo
Enlightened
- Joined
- Dec 23, 2004
- Messages
- 461
Can someone give a simple procedure for "matching" cells for a pack? I am going to rebuild a pack for my bike light (9 x 4/3A NiMH). So, I should get a few extra and then select by what criteria? Discharge to a certain pack voltage and then measure individual batts? For volts, amps, both? I don't have much sophiticated equipment. A simple multimeter and for a load I've got a 12V 35W car foglight bulb. Good enough? The device itself pulls about 1.25A, but I'm not going to use it for draining/testing 'cause it's an HID and I don't want to bother with fans or eat away the bulb life.
What's a reasonable number of extra cells? These guys run about $6 (Sanyo "Twicells"), so....
Thanks
Last edited:
SilverFox
Flashaholic
Hello Nubo,
Cell matching is a "labor of love." It is time consuming, but I think the results are well worth the effort.
I start by breaking in my cells. First a 0.1C charge for 16 hours and a discharge to check for initial capacity. I then do a few cycles of 1C charging and discharging.
Now you have 5 - 10 cycles on your cells, and you are ready to match them. If I have a particular application in mind, I will match them at the same current draw that the application uses. If not, I will match them based on a 1C draw. Remember that a 1C draw will drain your cells in 1 hour.
Charge your cells, hook up your batteries to your load and time how long they last. Your first match is on run time, or capacity.
Next you need to pick a time part way through the total run time. I prefer to pick a point half way through. Now you need to measure the voltage, under load, at this point. This is referred to as mid point voltage. This takes into account the effects of the cells internal resistance. This is the second match.
These are the main two matching points, but some people also take note of the voltage the cells rebound to after discharge.
A look at the math involved includes averaging your capacities and mid point voltage values. If you have a wide variation, throw out the highest and lowest numbers. Capacities tend to vary more than mid point voltages, so I generally match to 5% on capacities and 2% on mid point voltage. If you are wanting a closer match go with 2% on capacity and 1% on mid point voltage. Keep in mind that the pickier you are the more cells you will need to come up with a set that "matches."
Here is a real world example. I started with 18 cells. The mid point voltages were all within 1% of the average, so this match point did not factor in. Matching the capacities at 5% gave me 17 cells that I could use, and matching capacities at 2% gave me 11 cells. 6 of those 11 cells matched to within 1% of capacity.
If I wanted to match to 1%, I would end up with 6 out of 18 cells. If I wanted to match to 2%, I would end up with 11 out of 18 cells. Finally, if I wanted to match to 5%, I would end up with 17 out of 18 cells.
As it turned out, I matched on 2%, and one of the cells died during further testing. My yield was 10 our of 18 cells.
You will have to decide what degree of matching is important and how far you want to go with this.
Tom
Cell matching is a "labor of love." It is time consuming, but I think the results are well worth the effort.
I start by breaking in my cells. First a 0.1C charge for 16 hours and a discharge to check for initial capacity. I then do a few cycles of 1C charging and discharging.
Now you have 5 - 10 cycles on your cells, and you are ready to match them. If I have a particular application in mind, I will match them at the same current draw that the application uses. If not, I will match them based on a 1C draw. Remember that a 1C draw will drain your cells in 1 hour.
Charge your cells, hook up your batteries to your load and time how long they last. Your first match is on run time, or capacity.
Next you need to pick a time part way through the total run time. I prefer to pick a point half way through. Now you need to measure the voltage, under load, at this point. This is referred to as mid point voltage. This takes into account the effects of the cells internal resistance. This is the second match.
These are the main two matching points, but some people also take note of the voltage the cells rebound to after discharge.
A look at the math involved includes averaging your capacities and mid point voltage values. If you have a wide variation, throw out the highest and lowest numbers. Capacities tend to vary more than mid point voltages, so I generally match to 5% on capacities and 2% on mid point voltage. If you are wanting a closer match go with 2% on capacity and 1% on mid point voltage. Keep in mind that the pickier you are the more cells you will need to come up with a set that "matches."
Here is a real world example. I started with 18 cells. The mid point voltages were all within 1% of the average, so this match point did not factor in. Matching the capacities at 5% gave me 17 cells that I could use, and matching capacities at 2% gave me 11 cells. 6 of those 11 cells matched to within 1% of capacity.
If I wanted to match to 1%, I would end up with 6 out of 18 cells. If I wanted to match to 2%, I would end up with 11 out of 18 cells. Finally, if I wanted to match to 5%, I would end up with 17 out of 18 cells.
As it turned out, I matched on 2%, and one of the cells died during further testing. My yield was 10 our of 18 cells.
You will have to decide what degree of matching is important and how far you want to go with this.
Tom
Having used the new Elite 1700AA vs. CBP 1650's which are no longer made, I can say the 1700's are better cells, but for 5A (or less) applications, they are probably not the ideal cell. They excel at >6 to 10A applications such as driving 50 - 100W incan bulbs. For most applications, the Eneloops do a nice job and have the LSD benefit. Use Tom's battery charts.
