MK 12 volt battery question

[Seki]

They said that we could ONLY use the MK 12 volt battery as our maing power battery, aren't they the same as last years batteries? the previous years batteries are 12 volt, can we still use them?

anyone know?

-Thanks

[bear24rw]

The batteries are slightly different from those last year. I'm not sure of exact specs. You are not aloud to use batteries from last year as this would create an unfair advantage to those teams who dont have those batteries from last year

[John Gutmann]

Originally Posted by Seki

They said that we could ONLY use the MK 12 volt battery as our maing power battery, aren't they the same as last years batteries? the previous years batteries are 12 volt, can we still use them?

anyone know?

-Thanks

It is not the voltage of the battery that is different. It is the model number. If you would go look at your batteries from previous years you would notice the are exide ES-xxx* model number. EX-xxx* != MK 12

-John

*I do not know the exact model number off hand.

[Richard Wallace]

Specs for the 2007 battery are here.

Specs for the 2006 battery are here.

The new one appears to have about 10% less stated capacity at 1C discharge rate. So if you could use the older battery you might get an advantage over a team using the new one -- which is almost certainly the reason why the older ones are not allowed this year. For more, see this post.

[Karthik]

Originally Posted by Richard

Specs for the 2007 battery are here.

Specs for the 2006 battery are here.

The new one appears to have about 10% less stated capacity at 1C discharge rate. So if you could use the older battery you might get an advantage over a team using the new one -- which is almost certainly the reason why the older ones are not allowed this year. For more, see this post.

Richard,

There are some major differences between the two sections of spec sheets you posted.

Originally Posted by ES17-12 Spec Sheet, Top Section

Maximum discharge current (A) 5 sec: 90

Originally Posted by ES17-12 Spec Sheet, Bottom Section

Maximum Discharge Current for 5 seconds: 720 A

That's a huge difference. The Exide battery from 2006 had a 230A max discharge. Can anyone confirm which of these is right? Am I missing something here? If the max discharge has dropped all the way to 90A, we'll definitely be reconsidering our motor usage.

[Richard Wallace]

Originally Posted by Karthik

There are some major differences between the two sections of spec sheets you posted. ...

I'd guess that the 90A figure in the top section is an error. The lower section shows 360A maximum discharge current for 30 seconds. Also, the discharge time vs. discharge current curves shown near the bottom indicate several minutes capability at 3C (54A) discharge current; this is similar to the 3C capability of the older battery. It appears the new and old batteries are similarly constructed, and that the new one is designed for slightly (~10%) lower capacity. This may be a design trade-off to allow higher short-duration discharge currents. (A little more lead, a little less acid.)

[Al Skierkiewicz]

Karthik,
The specifications on the MK site are very close to the specifications for the old battery. The differences are slight enough to merely be differences in testing methods or the influence of the marketing departments. A close inspection of the discharge curves show that they are at slightly different currents from the batteries we have used in the past. A quick interpolation of the data would show them to be almost identical. Let's face it, a battery of the same physical size and chemistry with the same amp hour rating is going to be pretty close in performance. You can only pack so much lead and acid into that package. I hate to have to buy new batteries this year but if those are the rules then so be it.

[Mike AA]

As I am reading this chart it seems the new battery has a HIGHER discharge rate. 5 seconds @ 720A this years battery and last years battery is 5 seconds @ 230A. Therefore it would better seem the new battery is BETTER for burst and a quick pushing match...

-Mike

[Al Skierkiewicz]

Mike,
Although that specification looks different, last year's battery was capable of the same high current for short periods and when new and fully charged. "Your mileage will vary." In fact most teams will not be able to draw this kind of current simply because there are other limiting factors like the combined resistance of the wiring, breakers, speed controllers and connectors.
Remember that the real test will be how much you can draw over a two+ minute match and remain above 8 volts, the critical cutout for the RC.

[pyrr101]

Reading the label on the battery, this years battery is 18AH instead of last years 17AH.

The R46 rule says the use of batteries different from or in addition to the ones provided, nothing about more then one on a robot.

This can be read as the ones given in the KOP are the only ones to be used on the field.

[ntroup]

First of all, last year's battery was an Exide ES 18-12 (or the EX 18-12, in some cases), which is the same battery that we have used for many years, and it is indeed an 18AH battery. Many people have linked to the datasheet for this, so you can confirm there.

Also, as stated before, <R53> clearly states that we CAN purchase additional MK batteries for use during the competition. <R46> states that you can not use more than one battery on the robot during a match.

-Nate

[Erro]

It appears that the new batteries should not have a great effect on teams. MOE only uses the new batteries in competitions any way, and the old ones are perfectly legal for practice. As always, we're always willing to share with other teams, just let us know you need them

[dcbrown]

The 10% difference sited on old vs new battery may or may not exist. The old battery specs its 9Ah at 0C/32F. The new battery specs its 8.1Ah at 25C. Specmanship in play as the temperature of the measurement is important.

The old battery lists 9AH with a 18A (1C) draw at 0C/32F temperature.
It also has a curve for 20C/68F which shows roughly something like ~7.5Ah-8Ah (hard to get exact with the log graph shown but looks like 24+/-2 minutes until 100% depth of discharge (DoD) is reached).

The new battery lists 8.1Ah with 18A (1C) draw at 25C, about 27 minutes to 100% DoD. The actual discharge graph only shows a 17A discharge curve, but it too looks to be in the 28 minute range to 100% DoD.

http://www.rpci-inc.com/pdf/ES17-12.pdf

I overlaid the discharge curves between old/new. The 17A/18A are green/red curves. What is more interesting are the 36A (old) vs 34A (new) curves. The 36A (old) curve shows 100% DoD at about 16-18 minutes vs 34A (new) curve shows 100% DoD at about 9-10 minutes. The voltage drop under load favors the new battery which maintains a much higher voltage output under similar load. This was confirmed by a quickie test using a 50A dummy load on last year's ES18-12 vs this year's ES17-12. The ES17 had a ~.2-.3v higher voltage while under load. Load was held for 20-30 seconds.

The batteries are close, but are different and diverge at larger discharge rates. The biggest difference seems to be the maximum spec'd discharge; 230A (old) vs 720A (new). Greater safety margin?

Bud

[Seki]

Thanks guys for helping.
I needed to know quick so we oculd get a few more ^_^

[lopz056]

hey all.i been looking all over,but i cant find where to buy a 12v 18ah mk-battery, if any of u guys would be so kind to email me a link to a good supplier, cheap would help, i would be very appreciative, my email is fortyniner_fan056@yahoo.com