3
\$\begingroup\$

I'm looking for advice to how to replace a Duracell TR163 mercury battery in an old synthesiser I have (Oberheim OB-1 if anyone is interested). The battery is no longer available, at least not in the UK, so I'm looking to see if I can replace it with a circuit or some other type of battery. The battery itself is rated as 4.05V and 500mAh so I'm thinking that using 3xAA batteries and reducing the voltage from 4.5V to 4.05V would work. I'm very much a beginner with electronics and there seems to be several options (voltage divider, diodes etc) however I've not been able to find this specific situation to use as a reference.

My concern is that I don't know whether the load is fixed or variable so I'm not sure a voltage divider is sufficiently safe. I believe the battery powers the patch memory when the device is powered off but I don't have any more details at the moment.

Ideally I'd like some sort of rechargable battery system that is charged from the main power board when the synth is running, but that's probably reaching too far!

Any advice would be most gratefully received.

\$\endgroup\$
10
  • 1
    \$\begingroup\$ In that voltage range you may get away with a simple LIPO battery which is usually charged to 4.2V max. Simple, cheap charging circuits are available, many intended to operate from USB's 5V. So if you have a 5V rail, that might just work. Though those parts probably operate well beyond 5V, but haven't checked the specs. \$\endgroup\$
    – JimmyB
    Jun 9, 2017 at 16:11
  • 3
    \$\begingroup\$ How is this question off topic when the OP is asking for a circuit for his power supply needs?! \$\endgroup\$
    – JimmyB
    Jun 9, 2017 at 16:19
  • 4
    \$\begingroup\$ Voting to re-open. It's not really a shopping question because you can't buy mercury-zinc anymore. The question "how do I replace a TR163 with a modern alternative" seems to be a good, on-topic question. \$\endgroup\$
    – Jack B
    Jun 9, 2017 at 16:41
  • 4
    \$\begingroup\$ It is stated as an engineering design problem rather than shopping for an off-the-shelf solution, and I personally think worth re-opening on that basis. There is a legitimate counter argument though, in that it is an under-specified problem, since so far we don't know which aspects of the original battery are important, if the replacement needs to fit in the original space, etc. \$\endgroup\$ Jun 9, 2017 at 16:56
  • 3
    \$\begingroup\$ The schematics are at "synthfool.com/docs/Oberheim/Oberheim_OB1/…". Page 4 has the battery and it is only used as a backup supply for some CMOS components with 15v tolerance - it doesn't need to be accurate. It supplies the normally 5v rail through a diode. Any voltage between 4v and 5v would be suitable - your 3x AAA batteries would be a good substitute. \$\endgroup\$ Jun 9, 2017 at 17:23

2 Answers 2

2
\$\begingroup\$

The TR163 is a 3-cell mercury-zinc battery (be sure to take the old one to proper disposal!). Mercury-Zinc chemistry was favored for equipment design because it had a very flat discharge curve that output about 1.35v (per cell) for most of the service life.

Given the expectation of a flat discharge, you probably want a higher voltage pack and a good low-overhead, low-loss regulator, rather than subjecting the equipment to the substantial voltage variation of today's available chemistries.

Measuring power consumption using an adjustable power source would be a good first step to sizing.

You will also need to consider usage patterns - for example if this is a memory backup source that needs to be available while sourcing tiny currents you would would need to carefully select a regulator with low quiescent current. If usage is more intermittent you may be able to use an everyday regulator and put a switch in the circuit, or even only install the replacement cells when the device is to be used. Noise sensitivity may guide if you can use an efficient switching regulator easily, or if that would require extreme care in filtering.

If you can determine that the equipment will tolerate slight over voltage, NiMH cells might be a crude replacement, but fresh off the charger their voltage can be too high, and they will quickly drop to something closer to 1.2v per cell before somewhat leveling out.

The vintage camera community often faces similar problems with retired battery types; there may be helpful resources there.

\$\endgroup\$
1
  • \$\begingroup\$ 3rd party comments on the device to be powered now make it sound like the requirement isn't very strict at all. \$\endgroup\$ Jun 9, 2017 at 18:44
0
\$\begingroup\$

If it's non-rechargeable, which I think is the case, you can replace it with any battery of equivalent voltage.

From a book, I see it is 4.05V, 500mAh (this is the capacity, how much energy it holds). I wouldn't a priori recommend 4.5V unless we can be sure we're not frying nothing since it's more than 10% above rated. Most probably it's ok, but why risk?

Probably the only use of that battery is to hold all your presets so that you don't lose them every time you unplug it.

Rechargeable 3.7V batteries have a charged value of 4.1V normally. This is the case for LiPo cells but this are rechargeable.

\$\endgroup\$
11
  • \$\begingroup\$ Any recommendations as to which battery outputs 4.05V? \$\endgroup\$
    – JimmyB
    Jun 9, 2017 at 16:08
  • \$\begingroup\$ Is it still working? Try measuring with a multimeter the votltage you have now. It's easy to get 3.6V batteries (amazon.com/Saft-LS-14500-3-6V-Lithium-Battery/dp/B002GK406C) but it might not be enough. \$\endgroup\$
    – Andrés
    Jun 9, 2017 at 16:11
  • \$\begingroup\$ If you want a rechargeable battery look at this: adafruit.com/product/1904 they're small lipos that charge to 4.2V so that should be ok. It comes with a charger as well. But you shouldn't charge it while it's working. When you need to charge the synth just make sure it's plugged and then remove and charge the battery and all your presets should be held. \$\endgroup\$
    – Andrés
    Jun 9, 2017 at 16:15
  • 1
    \$\begingroup\$ In theory a custom LiPO charger could be built which would stop the charge at only 4.05v (and this will actually yield longer cell life, at a reduction in capacity). However, the voltage will drop in use much more steeply than the original mercury-zinc battery. Additionally, discharge of the LiPO cell must be stopped at a reasonable voltage or it will be permanently damaged. \$\endgroup\$ Jun 9, 2017 at 16:22
  • 1
    \$\begingroup\$ Keep in mind Alkaline AA's can be something like 1.7v for a brief time when new. \$\endgroup\$ Jun 9, 2017 at 16:59

Not the answer you're looking for? Browse other questions tagged or ask your own question.