How to replace batteries in an AMB Tranx 260 racing transponder

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Transponders are expensive. To me, inexplicably so, which is part of why I’ve never owned one. I pay the $50 rental fee whenever I run a LeMons race and grumble to myself about why a plastic box with some simple electronics and nothing-special NiCd rechargeable batteries would cost more than a GoPro.
A transponder with a dead battery fell into my possession. It sat in my garage for a few years before I finally took the time to crack it open. Hit the jump to find out how you can try and revive a dying TranX battery.

If you’ve ever taken the cover off a transponder, you’re familiar with the stuff what fills it. It’s some kind of hard foam resin, nearly impossible to cut or chip away at. I couldn’t find any very detailed information on how to replace the batteries in one of these except for a video or two, and many references to a company called Transponder Services in Queensland, Australia, owned and operated by Jeff Chandler.
Many people seem satisfied with his services and are willing to pay the US$90 to get their transponder fixed. I’m an experimental type and I had a free transponder. I had nothing to lose in trying this myself. Besides, the resin in mine was already cracked between the battery and circuitry. But I did consult Chandler for his opinion. He produced some important warnings and caveats for those trying this out themselves, the most important of which are:

  • In most cases the old battery is leaking. You should wear rubber gloves and wear a mask. [It was too late for me when I found out, but I am not dead yet.]
  • The old battery should not be disposed of in general waste. Correct disposal is at a hazardous waste depot. [Ditto above, but I’m not proud of it.]
  • You can’t convert a battery-powered transponder to a hard-wired one. If it were possible, he would definitely be offering that service.

Click here to find a battery recycling center near you.
Before continuing on to my process and experience, here’s what Chandler had to tell me about his experience with do-it-yourselfers.

In the 14 years I have been providing this service I have seen many transponders wrecked beyond repair by well-meaning DIYers. I’m not scare-mongering or trying to drum up more business because I get enough to keep me occupied anyway. I am kind of semi-retired, but not old enough for the pension yet, and financially in very good shape.
The DIY repairs that I end up seeing are either damaged beyond repair or done badly. Initially the transponder worked for the DIY person but failed later. There is a small club transponder that RC model car racing rely on which are no longer made. This is the AMB20 and AMBrc.
In a club there is usually a well-meaning person with some good skills that has a crack and fixing these and either opens one or two and gives up and has possibly killed the transponders in the process, or they are successful and do the whole set of 10 or 20.
The problem is they commonly do several thing wrong which sets up a nasty chemical reaction which over time eats into the guts of the transponder and they stop working and cannot be repaired. [He wouldn’t specify.] I’ve seen many of these and it is an ugly messy sight and in some cases I can clean it up and get them working again.
I understand people wanting to have a go at repairing their transponder themselves but IMHO it is better to save yourself the hassle and have it done by someone that has the experience to do it right.
I have seen a variety of “tutorials” “I did mine like this” posts online (some in forums) for various types of transponder battery replacement and as yet I have not seen one that has the correct instructions and in many cases the methods are dangerous and done the difficult way. [He refused to give any more specific details about this.]

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Armed with what little information I had, I set to work attempting to repair my own transponder so I could create a post online that illustrates the process in a potentially dangerous and difficult way. If you want to attempt this yourself, you do it at your own risk. Obviously. Sheesh.
I heated the transponder in my oven at as low a temperature as it would do, for about 30 minutes. This softened the resin. I cut off part of the plastic case and separated battery, which was already swollen and leaking before I even started. Then I started cutting away at the resin around the battery in order to read the label.
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The battery was made up of 3 individual rectangular nickel-cadmium (NiCd) cells wired in series, for a total of 3.6 volts, and 1350 mAh of capacity.  I did a lot of searching, but couldn’t find anything that fit those specs and the rather small dimensions of the transponder. I couldn’t find any rectangular batteries at all. But, ignoring one packaging constraint, I found something for less than $20 shipped on batteryspace.com. Part No. CU-J605 has the same output voltage and higher capacity, and comes with solder tabs.
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I had already made a note of which side held the positive terminal based on the battery I took out. I decided while shopping that I don’t know anything about batteries, so rather than pursue a nickel-metal-hydride (Ni-MH) or  lithium-ion (Li-ion) or other higher-tech replacement battery, I figured I’d stick with NiCd. That way I know there won’t be incompatibility with the charger, transponder circuitry, temperature range, or any such thing.
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I dug at the resin until I could access enough of the original battery leads and soldered it all together.
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Then I put it on the charger. The charger output of 200 mA and a total battery pack capacity of 6600 mAh, I figured it would take a day and a half to charge. That turned out to be about right.
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The question mark I had was how long these new batteries would last. These transponders have an LED indicator that blinks, in green, how many days of life there remains in the battery. When there is less than 1 day left, it will blink red. If it blinks 3 times, you’ve got 3 days. Simple.
When I took this off the charger, though, something strange happened. It blinked red.
It blinked a single red flash for a solid 2 or 3 days. Then it started flashing in green, 6 times. A few days later, 5 flashes. Then, less than 20 hours after that, it was dead.
Like I said before, I know little about batteries, and the expert on these things isn’t going to spill much useful information. I speculate that whatever comparative circuit in the transponder calculates the amount of battery life left can’t properly understand the capacity or the discharge rate of these super-huge batteries.  If you are knowledgeable in this realm, let me know in the comments.
Regardless, I think the process worked and am looking forward to an opportunity to try it out. If you’re the adventurous, hands-on type and don’t mind having a transponder that looks a bit like Max Headroom, this might be a worthwhile experiment for you, too.

About Alan

I'm a giant nerd and lifelong iconoclast who happens to like cars, especially terrible ones. I've built many low-budget race cars, driven in many Lemons races, worked at a Real Deal Print Car Magazine, and gave up that lifestyle in the interest of life balance. I also wear khakis and ride bicycles, though rarely at the same time.

4 Comments

  1. Always worth a shot. I don’t race nearly enough to see a decent ROI on a transponder purchase. I’ll continue to rent with the added benefit that I know that what they rent me works with their equipment.
    Then I put it on the charger. The charger output of 200 mAh and a total battery pack capacity of 6600 mA, I figured it would take a day and a half to charge. That turned out to be about right.
    You have your units mixed comparing the battery and the charger. The battery is rated in mAh, and the charger in mA.

  2. “and grumble to myself about why a plastic box with some simple electronics and nothing-special NiCd rechargeable batteries would cost more than a GoPro.”
    This is a conversation more people need to have. It’s maybe $20 worth of hardware? Sure there’s the fancy server side stuff, which you pay for once in the price of the transponder (well now you get to pay for it annually thanks to flex), which does cost some, but for a non-commercial user you’re talking 1 or 2 times a YEAR?
    I think rental is the only appropriate route for hobby/amateur racing. That is until facilities finally switch over to RFID systems. They work up to crazy fast speeds now.

  3. Well, I replaced the battery in a 15 year old (red case) AMB Tranx 260 about 7 or 8 years ago. I had it from new & it was not obviously damaged in any way, just wouldn’t take a charge any more.
    I saw an article somewhere where they showed roughly how they’d done it by cutting the case, which looked like a mess but is obviously a very simple method, just difficult to make tidy again. I’ve seen a few like this. I did it the harder way.
    Seeing which side the battery was on I carefully drilled an AA battery sized hole in the top with a forstner bit. Then I cut the grey bottom cover off by working around the join to the main case with a Stanley / craft knife. The only thing visible after this was the very hard resin.
    After that it was a lot of time drilling & cutting out the resin around the battery with a craft knife. V slow, tedious & patient work.
    Eventually the battery appeared & I worked my way in & cut off the tabs. They were very short & spot welded to the battery. It took quite a bit more drilling down the sides of the battery with long thin bits to start getting it loose. Then I pushed it out in stages in a vice with a small socket on the battery (-) end, which is at the top.
    Trouble is, the drilling & pushing ruined the battery plastic cover / label so it was hard to tell what it was. It was a few mm taller & bigger dia. than a std AA. Some sort of 18xxx I think. Kind of a military-industrial spec. AA.
    Looking at the AMB charger it says 12vdc 40mA. So to my tiny mind that means its a 12v battery. I’m pretty sure the original forum I saw mentioned it being 12v so I found the biggest capacity NMH (2700mA) I could find & fitted it. It lasted the 7 years or so until now. I replaced it again with an identical battery but that one has died in less than 6 months. So it’s back to the drawing board. I think the yellow case 160’s will have some differences. Is it possible your weird square batteries actually needed to wired in parallel, giving 1.2v? Particularly as it packed up working so quickly.

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