Battery Replacement

What is the correct battery for my Accutron?

The Tuning Fork watches manufactured by Esa (e.g the f300 Omega) were designed to run on either mercury or silver oxide batteries without any adjustment, provided the last repairer to work on the watch set up the index mechanism according to factory specifications.

It is strongly recommended that you do not replace batteries yourself, as special tools are required to open the watch case without damaging it. The only exception to this is the Accutron 214 model, which has a small battery hatch on the back.

Do not use batteries based on any other cell chemistry than silver oxide or mercury, or severe damage to your watch may occur due to leaking chemicals or gas, which have nowhere to dissipate in a sealed watch except onto all the working parts. This applies especially to Zinc-Air cells, which at first glance may appear to be a good alternative to mercury batteries. To find out more about watch battery construction and chemistry, click here.

My watch runs fast or erratically with the new Silver Oxide Battery. What is wrong?

This is due to a phenomenon known as "double indexing". Double indexing occurs when the amplitude of vibration of the tuning fork increases to a point where the index jewel picks up 2 teeth on the index wheel, not just one as it should. The amplitude of vibration of the fork has increased because of the higher voltage of the Silver Oxide cell. For a complete description on how the index mechanism works, click here. It's well worth taking the time to read and understand this.

Can this be corrected by "re-phasing" my watch?

Sometimes, the watch can simply be re-phased, and it will run fine, though very likely the built-in "safety factor" (described below) will be lost. More often than not, something else will need to be done to correct the problem. Most repairers "mix-n-match" coil sets and tuning forks to get a combination that works. Due to manufacturing tolerances, some forks vibrate at a slightly higher amplitude than others. The hope is to find a coil set/fork combination that works ok. This can be a very laborious and frustrating process, not to mention the extra wear and tear inflicted on the movement by having to dismantle it so many times. Another method I have heard of is that some repairers increase the tension on the index and pawl fingers, hoping that the increased load will reduce fork amplitude. Needless to say, this is a practise which can only have disastrous consequences in the long run, as it will eventually destroy the index wheel.

There is a better way of solving this problem

One of the problems of both the re-phasing and the mix-n-match technique of solving the double-index problem is that the "safety factor" built into the index mechanism is lost. This "safety factor" is the difference between the vibrational amplitude when a fresh cell is installed, and the amount of amplitude required to cause double-indexing. The safety factor is necessary to stop movements and knocks from normal daily use of the watch causing the occasional double-index, and thus causing the watch to slowly and intermittently gain. There is only one way to satisfactorily solve this problem. This is to fit a regulating device to the watch which drops the voltage supplied to the Accutron electronics to a level it was designed for. I offer a repair service to do this. Click here for more information.

What about Accucells?

UPDATE: 16th July 2006. Well it sure has been a long "2-3 weeks" since I promised to give you updated info on Accucells! My apologies...there has been a lot of water pass under the bridge since then - not the least of which is I have since remarried and have been living in Thailand for the past 5 1/2 years.

Since the first generation Accucells came onto the market some 7 years ago, they have undergone a process of refinement and development. I am now pleased to report that the "2nd Generation" Accucells that are now available are a significant improvement on the original design, and in fact now embody the same electronic principles that I use in doing coil modifications to Accutrons to make them compatible with Silver Oxide cells. Hence, they now deliver the correct voltage to allow an Accutron to start and run within their original design specifications. In fact, I am inclined to think that Accucells are now a more satisfactory solution than the coil modifications which I proposed in the past, especially for those watches which won't readily adjust to run on Silver Oxide cells.

There is only one negative issue with Accucells, and that is the design of the Accucell requires that a slightly smaller cell is used than the original cells, and this means that the time between cell replacement is reduced from 12-15 months to about 9-10 months or so. This is simply because the power stored in a cell is proportional to its physical size and the amount of active chemicals that can fit in it.

So, rather than modify your Accutrons, I strongly recommend that you consider using an Accucell if you are having problems with double-indexing and your watch running fast. As for owners of Omega f300 watches, and others that are based on the same movement (ESA 9162, ESA 9164, ESA 9210, and the micro-motor tuning fork watches Omega cal 1220, cal 1230 Megasonic f720hz), there should not be a need to use Accucells, as those movements were designed to run satisfactorily on the higher voltage Silver Oxide batteries as well as the Mercury based batteries which have been phased out now.

If you wish to purchase Accucells, (manufactured by Clark Watch Parts), please visit their Ebay store here. Their ebay user name is nostalgia-2000.

UPDATE: 2nd May 2000. The manufacturers of the Accucell have advised me that the cell I tested below is an early model, and some changes have been made to the design since then. I am awaiting a sample of the new design for evaluation, and when I have done this (in 2-3 weeks time), I will report my findings here. So, treat the following information as "preliminary only".

Accucells can work for some watches, though the reduction in voltage they provide is so slight as to be almost a waste of time. However, it may be just enough to "kick you watch over the edge" and make it run ok. Once again, as above, the safety factor is lost, at least until the cell's voltage has dropped as it approaches the end of its useful life. An Accucell is simply a standard 395 cell fitted with a 3.9K resistor to drop the voltage. See pic below. While that sounds like the answer, this method is based on an incorrect engineering principle, namely, that the current drawn by an Accutron is constant. In order to get the watch to start when the Accucell is inserted, the Accucell resistor value has to be low enough to allow the current required (up to10 times the normal running current). The result is that when the watch is running, the volt drop provided by the resistor is almost insignificant. On a 214, the volt drop is only 0.03v - or less than 2%. The voltage drop needs to be 0.2 - 0.25 volts (or between 12 and 15%) to be satisfactory. Another disadvantage is that the smaller 395 cell as used in the Accucell has about 15% less capacity - and therefore 15% shorter life - than a 387S or 394 cell.

Components of the Accucell