Measure battery voltage without removing cover!

[khutch]

That's odd, for me the link goes to Amazon in the US and the price is $19 and change....

 

[ddnidd1]

That's odd, for me the link goes to Amazon in the US and the price is $19 and change....

The original link goes to Amazon in Canada. However if you're in the US, it defaults to Amazon in the US with the $19 price.

Regardless, the item on the Canadian site is priced at $13.85 US, but they don't ship to the US.

 

[khutch]

The original link goes to Amazon in Canada. However if you're in the US, it defaults to Amazon in the US with the $19 price.

I am in the US and I posted the original link and the price I saw when I posted it was $19.69 and that was on the Amazon.com site. It must be that the link (or TB?) defaults to Amazon.ca for Canadian members.

 

[ddnidd1]

Yeah it was mentioned previously the link went to amazon.ca so I guess that person is in Canada.

 

[DiabolusInMusic]

Yes, I am in Canada. I can shop at Amazon.com, I would think you can shop at .ca (although, this seems to be a restricted item.) Even at $14 + shipping, it is still probably cheaper to get it in America for $20. I am pretty sure Amazon ships with Fedex internationally.

I am guessing this has to be some kind of error in the system. All other .ca retailers sell it for $40~. I am probably just going to sell them on kijiji for $15 and get mine for free.

 

[FatFunk]

Hi there.
I had no idea I could measure the battery voltage via output jack... Sounds exactly like what I'm looking for.
So I can just stick an unconnected TRS plug and measure with a multimeter?

 

[ddnidd1]

Hi there.
I had no idea I could measure the battery voltage via output jack... Sounds exactly like what I'm looking for.
So I can just stick an unconnected TRS plug and measure with a multimeter?

Yes - or a TRS cord (both plugs TRS) and just measure from the unconnected plug end.

 

[boynamedsuse]

If you are really worried about your battery life and especially if your bass does not have an active/passive switch that will let you play on with a dead battery, then having some means of checking your battery voltage is a very good thing. The OP's method is fine and in theory it will work with any bass. The method of checking the battery through the output jack does work on my active Fenders and on the Ibanez SR505 I once owned. There is indeed a meter built especially for this application, that link goes to Amazon but of course it is available at many places and I am not shilling for Amazon, use the one you like best. Oh and of course eventually that link will break so for the benefit of future generations of bassists the meter is called the Batt-O-Meter and is made by Keith McMillen Instruments. As noted above you can also test batteries in most basses with a simple voltmeter connected between the "ring" and "sleeve" of a stereo (aka TRS) cable plugged into your bass. Whether you use the Batt-O-Meter or an ordinary voltmeter there will be some voltage loss in the preamp when you measure the battery voltage in this way. On the basses I have checked it is between half a volt and one volt of loss, so you need to add that value to the voltage that you measure to get the true battery voltage. You can compare inside (directly across the battery) and outside (through the output jack) measurements to get the value for your particular bass. This value could vary a fair amount from preamp design to preamp design and obviously the Batt-O-Meter either ignores this or uses some average value to estimate the voltage.

Personally, I have been using a home made circuit to monitor the battery voltage in my basses and light an LED in some pattern to notify me that the batteries are approaching their end of life. Essentially the same thing as the John East device although this is the first time I have seen mention of it. Works pretty well in my 9 V bass. Not so well in my 18 V bass. I think I need to increase the trip voltage in my 18 V bass. Being cheap I set it pretty low, maybe 6 or 7 volts. Trouble with that is that the two batteries in series in an 18 V bass do not have identical capacities and so for the second time now I have seen my bass go dead (it has an A/P switch so I am good) without triggering the circuit. What appears to be happening is that one battery is still above my trip point while the other is not only dead, zero volts, it gets reverse charged by the current the other battery is sourcing. When I first plug in the bass the good battery is powering it normally and my LED gives me the good to go sign. I've been playing a lot in passive mode lately and I ignore the battery monitor while playing. While I am playing the dead battery's reverse voltage rises and eventually must trigger my circuit but I don't notice this while playing in passive mode. Typically by the time I stop playing the dead battery's voltage is so high the circuit no longer functions so the circuit is still not giving me any warning. By the next time I play the bass the dead battery has recovered enough to allow the cycle to repeat. So a word the wise DIY battery monitor builder: set the trip point ABOVE the 9.5 V a single fresh battery gives you. I think this will guarantee that your circuit will function as you expect and by the time the series voltage gets down to 10 or 12 volts, you have gotten all the good out of those batteries. If you try to push the trip point lower to get more out of the batteries you might as well not bother to build the circuit!

If you believe the manufacturers the shelf life of current alkaline batteries is better than it ever has been, for the name brand batteries anyway. If you believe them....

Good to know. Two of my active basses are 18V. I will be investigating this further. Thank you.

 

[megafiddle]

Personally, I have been using a home made circuit to monitor the battery voltage in my basses and light an LED in some pattern to notify me that the batteries are approaching their end of life. Essentially the same thing as the John East device although this is the first time I have seen mention of it. Works pretty well in my 9 V bass. Not so well in my 18 V bass.

For a single 18V (unipolar) supply, it 's best to measure the series pair as if it were a single 18V battery. It's also best to always replace both batteries at the same time. Because they are in series, they should have equal lives; when one dies, the other will not be far behind.

With bipolar supplies (+9V / -9V), one battery may typically drain faster than the other; in this case it's best to monitor the battery that drains fastest. Unless one battery is lasting much longer, e.g. 2 years vs 1 year, these should also both be replaced at the same time. If replacing only one, the fresh battery should replace the one that is not monitored.

Referring to measuring at the jack, this only works with 3 terminal TRS jacks. Jacks with isolated switches are also in use, especially with bipolar supplies. With these isolated types, none of the battery voltages are present on the ring terminal.

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[James Copple]

There might be some other issue then; I just checked a bass with this method a moment ago to be sure I wasn't crazy, worked just fine.

What instrument is it? A few use a weird method whereby the hot of the 9V is switched, and those won't show voltage with this trick.

It's a Fender American Deluxe Precision Bass.

 

[James Copple]

For a single 18V (unipolar) supply, it 's best to measure the series pair as if it were a single 18V battery. It's also best to always replace both batteries at the same time. Because they are in series, they should have equal lives; when one dies, the other will not be far behind.

With bipolar supplies (+9V / -9V), one battery may typically drain faster than the other; in this case it's best to monitor the battery that drains fastest. Unless one battery is lasting much longer, e.g. 2 years vs 1 year, these should also both be replaced at the same time. If replacing only one, the fresh battery should replace the one that is not monitored.

Referring to measuring at the jack, this only works with 3 terminal TRS jacks. Jacks with isolated switches are also in use, especially with bipolar supplies. With these isolated types, none of the battery voltages are present on the ring terminal.

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Aha! This answers another question I had (I think). The wiring diagram shows the batteries wired in series with a red wire taking power to the circuit board. This wire was soldered to the wire from the board at a handy connection with a bit of shrink wrap covering the join. I tapped in to the batteries at this join, but to my confusion I only measured 9V instead of the expected 18V. Your post explains why, I think. However, if you could add anything more to help me understand better that would be great. Thanks@

 

[wmhill]

I've always replaced the batteries in my active basses once a year just to be safe. I've never had one die on me.

I have been changing them when the clocks change (a variation on the fire alarm thing). I used to do yearly, or more and still had no issues.....and I play a ton of gigs too.

 

[megafiddle]

Aha! This answers another question I had (I think). The wiring diagram shows the batteries wired in series with a red wire taking power to the circuit board. This wire was soldered to the wire from the board at a handy connection with a bit of shrink wrap covering the join. I tapped in to the batteries at this join, but to my confusion I only measured 9V instead of the expected 18V. Your post explains why, I think. However, if you could add anything more to help me understand better that would be great. Thanks@

Is this your bass?

[Invalid or Expired Link Removed]

The output jack in that diagram has more terminals than the basic Switchcraft TRS jack. The terminals used for the battery are very likely isolated from the other jack terminals. So then, the neg battery lead connects to one of the isolated switch contacts. The other isolated switch contact is jumpered to ground. The cable plug, when inserted, actuates the isolated switch and connects the neg battery lead to ground. You can't measure anything with a TRS plug, because there is no connection to the R terminal.

Do you measure 18V from your screw terminal to ground with an instrument cable plugged in? You're not going to get a battery voltage reading between the red (pos) battery lead and ground unless there is a cable plugged in.

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[Rob22315]

Good grief, don't do any of that. Just use the TRS cable to feed power from a good quality wall wart into the bass. You will have to short the internal battery connector with a second connector but that's easy anand reversible. I haven't put a battery in my active basses to at least 5 years now.

I built a small breakout box to separate the signal from the power.

We can avoid all the previous arguments against this. Yes, its not about saving money or not changing batteries once a year. Its about reducing the numbers of batteries I throw into landfills and not having to ever worry about a dead battery.

 

[megafiddle]

Good grief, don't do any of that. Just use the TRS cable to feed power from a good quality wall wart into the bass. You will have to short the internal battery connector with a second connector but that's easy anand reversible. I haven't put a battery in my active basses to at least 5 years now.

I built a small breakout box to separate the signal from the power.

We can avoid all the previous arguments against this. Yes, its not about saving money or not changing batteries once a year. Its about reducing the numbers of batteries I throw into landfills and not having to ever worry about a dead battery.

Yes, but you can't always do that for the same reason that you can't always measure the battery voltage at the jack: the battery terminal is not always available there.

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[khutch]

It is true that bipolar basses cannot be measured through the output jack. I'm not sure how common they are but [Invalid or Expired Link Removed]. For basses that use a single 18 V supply and most if not all 9 V basses you can measure the voltage by plugging a bare stereo plug in the output jack and measuring the right two terminals with a voltmeter. Once you have done that a few times you may decide to solder some wires and banana plugs to that stereo plug so you can directly connect your meter.

A problem with measuring both batteries in an 18 V bass is that you want a low power circuit that will not decrease the battery life too much, yet it has to handle up to 22 V if you put a fresh pair of Lithium batteries in the bass. A lot of low power comparators with internal reference voltages that you might use to make a battery monitor circuit are limited to less than 18 V. I finally figured out what I have done wrong with my circuit. When I made it the best small comparator I could find was an OnSemi unit with a max voltage of 10 V. So I connected it across only one battery reasoning that they should drain at the same rate and in fact the one with the comparator attached should drain a little faster. Yet twice now I have ended up with a dead bass because the OTHER battery is completely dead while the monitored battery has a ton of life left. Clearly something systematic is wrong here. Finally (just today in fact) I realized that there is a sneak current path through my battery monitor that prevents the non-monitored battery from ever turning off so it dies much quicker than the monitored battery. In effect it is always plugged in but not fully since it still takes about a year to drain.

So I have been poking around and I have found some comparators with internal references that take only a few uA of operating current yet can handle 27 V. These should make a nice battery monitor that can handle an 18V system. I will post a schematic once I've had a chance to build one up. I'd mention the make and model but I can't remember it right now! When I get to work tomorrow....

Ah, found it: Texas Instruments TPS3701

 

[megafiddle]

It is true that bipolar basses cannot be measured through the output jack. I'm not sure how common they are but [Invalid or Expired Link Removed]. For basses that use a single 18 V supply and most if not all 9 V basses you can measure the voltage by plugging a bare stereo plug in the output jack and measuring the right two terminals with a voltmeter. Once you have done that a few times you may decide to solder some wires and banana plugs to that stereo plug so you can directly connect your meter.

It all depends on the jack used. In the diagram I linked to above, the supply is 18V unipolar, but uses an isolated battery contact.

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[khutch]

It all depends on the jack used. In the diagram I linked to above, the supply is 18V unipolar, but uses an isolated battery contact.

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I was not rebuting you, I was linking to a different diagram just to show an example of a bipolar 18 V power supply. I actually had not noticed that we both linked to American Deluxe Precision Basses and I see now that this is confusing. However the confusion is the real world and apparently Fender switched to bipolar supplies some time around 2010 for some American Deluxe basses. If your bass has a unipolar supply and it uses a TRS output jack it can be rewired to allow external voltage measurement even if it does use an isolated switching contact to control the battery connection. You just move the battery ground to the ring contact on the jack. If it uses a mono jack with an isolated switch for the battery then the jack could be replaced with a simple TRS jack to allow external measurment. If your bass has a bipolar supply or if it is wired in stereo you are hosed....

... although in those cases you could add one or two DC power jacks somewhere that would allow you to measure the battery voltage externally. You could use other kinds of connectors for this but I would avoid using mini headphone jacks for this purpose because sooner or later someone will unwittingly plug a headphone into that jack! Replacing a complex jack with a simple TRS jack on a unipolar bass would allow the use of an external power supply for those of you who prefer to do that for whatever reason. If you have a bipolar bass you would have to use separate wires and jacks unless you can find 4 conductor quarter inch jacks and plugs. I know there are 3.5mm versions of this but I have never seen them in quarter inch.

 

[DiabolusInMusic]

I got my meters yesterday. It appears Amazon corrected the price somewhat, they are now $16 and change. I did not even get a chance to try one out yet though.

 

[James Copple]

Is this your bass?

[Invalid or Expired Link Removed]

The output jack in that diagram has more terminals than the basic Switchcraft TRS jack. The terminals used for the battery are very likely isolated from the other jack terminals. So then, the neg battery lead connects to one of the isolated switch contacts. The other isolated switch contact is jumpered to ground. The cable plug, when inserted, actuates the isolated switch and connects the neg battery lead to ground. You can't measure anything with a TRS plug, because there is no connection to the R terminal.

Do you measure 18V from your screw terminal to ground with an instrument cable plugged in? You're not going to get a battery voltage reading between the red (pos) battery lead and ground unless there is a cable plugged in.

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That is indeed my bass. I only get a voltage when I have a cable plugged in and the switch turned on. I only get a 9v reading.