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Q: can i power a (9v-battery) multitester with 8 or 10v? Answered

hi, i´m living in a mountain-cabin with a small solar-kit (12v battery, 6 x 2v cells).

i want to buy some multi-tester (which normally uses a 9v battery).

i hate to buy batteries (and not just becauce i am a cheap fukc - might actually cost about a bit less than the tester itself, go figure, beauty/beast of capitalism)

since i got anything from 2-4-6-8-10-12v here (for free - thank you sun): can i run the tester with 1 volt more or less? (or does all hell break loose .. which i´m actually kinda fond of)

bowing

Discussions

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the_3d6

17 days ago

The problem would be not voltage, but measuring precision. Battery provides super stable current supply with virtually no noise - so I suggest you to use a rechargeable battery. Any AC-DC or DC-DC converter will have a significant noise in its power line, and that inevitably would distort readings. If you want just to check connectivity or distinguish between, say, 3.5 and 3.7 volts - then it would work just fine (at least all my testers worked down to 7.5 volts battery before they became unreliable). But if you want to measure with 1% precision or better - then power supply noise might become a serious problem (it all depends on schematics of particular meter, so some might perform better that others, but to some degree it would affect any of them)

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la xerrathe_3d6

Reply 17 days ago

thanks. would a fluctuating input voltage somehow be corrected by an converter (if the output is adjusted to, lets say, 9 v)? or does any change on the input result in changes on the output? thanks again. xerra

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the_3d6la xerra

Reply 17 days ago

Multimeter's power schematics should compensate any voltage change in like 7.5-9.5v range (exact range depends on model), but high frequency noise from any dc-dc converter most likely would get through since power schematics isn't designed to filter it out - and that noise would cause quite unpredictable effects. I'd really recommend either 9v rechargeable battery or 2-cells LiPo battery (when charged more than 50% it would provide enough voltage)

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la xerrathe_3d6

Reply 15 days ago

thanks. more: that "high frequency noise" would come from...? i live off-grid, up in the mountains, power coming from a little solar-kit.... naughty HF noise dancing about here in the cabin?

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the_3d6la xerra

Reply 15 days ago

Virtually any DC-DC conversion that increases voltage, and efficient types that decrease voltage, are based on converting DC into high frequency AC and then this AC back into DC with a different voltage. Solar kits are not exception (except for the most inefficient ones that don't actually change voltage, just cut off if it's too high - but these are practically useless)

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la xerrathe_3d6

Reply 15 days ago

_A: since the battery from the solar-kit provides 2, 4, 6, 8, 10 and 12v i just hook it into 4x2v cells... i figure that provides as stable a voltage like a 9v-battery... no¿

_B: btw, since, as you say, all converters cause HF noise: how does tester-equipment that plugs into regular power-outlets (110 or 220v, etc) deal with it?

cheers

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the_3d6la xerra

Reply 15 days ago

Hooking it into battery would reliably filter low-frequency noise, but if you want to be safe - add 100nF ceramic (that's important) capacitor across battery's + and -, that would reduce HF noise significantly (battery is too "slow" to react on HF noise, and small ceramic capacitor is "fast").

All testers that plug into 110/220v have good input filters, it's really not complicated - a few capacitors after good LDO would do the trick. But tester that is designed to run from a battery doesn't have them

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la xerrathe_3d6

Reply 12 days ago

the capacitor i would leave inside the tester (f.e., with the 9v-battery clip)¿ ... it actually ´eats´ the HF noise?
btw, rigging some capacitator with a dc-dc converter wouldnt do the trick also?

ps, evidently i am stupid enough to ask questions, and you are patient enough to explain stuff... learning a lot, and, who knows, maybe in 1 month or 1 decade somebody comes across that post here and finds some seed, too. cheers again

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the_3d6la xerra

Reply 12 days ago

Your questions are perfectly valid :)
Low quality DC-DC when attached to a small load (like tester) could produce really high noise (tens of mV). But when attached to a battery, noise would be significantly reduced - battery takes most of it, although on higher frequencies it does it not as efficiently. So battery + capacitor result in a good enough filter.
If you want to attach it without battery, it's best to add a small resistor in series (~1 ohm), and both small and larger (5...10 uF) capacitors in order to be safe

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la xerra

4 weeks ago

hi, thanks for your comment. and, yes, of course my (knee+jerk)re+action towards batteries makes no sense (but then, if you go strip it all down to the essentials/, ultimately nothinkg makes sense. so, you might say, this is the only way i know how to kill time, or, more self-importantly put: my favorite one ).

that apart, why would i (want to) buy anything (like a battery) if i got enough toys (pieces..lego...) flying around here in the cabin that do the trick. you see, i made the ´choice´ (mind you: free-will is ´just´ another mental construct) to have very little $$ + a s´hit-load of ´free´time. some folks have a life (and buy batteries), other folks dont (and waste the day playing around like loonies).

thanks again (for the reality-check)

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Omnivent

4 weeks ago

Hi,
.
Considering how long even a half decent DVM runs on a PP3 (just use an eventual back-light sparingly), I really think it's a waste of life, components and transportability, to use anything but.
I have some DVM's go a couple of years or more on a PP3, so why jump through hoops to feed it - even if living on a mountain?
.
If you really want to do something, perhaps consider a rechargeable 9V battery -you'll have to recharge it maybe every moth or two, but at least the DVM keeps being transportable.
.
Have a nice day :)

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Orngrimm

7 weeks ago

At work, we use those for very convenient generation of Voltages for our Developers on a quick if they only habe a Notebook at hand and want to power some sort of PCB...
https://www.aliexpress.com/item/DC-DC-5V-to-1-2-24...
Feed anything 3.5V to 12V and get anything (Buck-boost) from 1.2V to 24V out.
If you need more power and only one direction of conversion (Boost like 6V to 9V OR Buck like 12V to 9V), i suggest one of those modules:
https://www.aliexpress.com/item/1pcs-Boost-Buck-DC...

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la xerra

7 weeks ago

a dc dc buck converter online goes for 1 euro .... this critter here feeds on 220v and excretes 9v (advantage: dont have to run xtra cable from solar-battery up in attic down into the cabin, but can plug it in a 220 outlet here). cost: 2.19 e

AC-220V-230V-to-DC-3-3V-5V-9V-12V-Step-Down-Converter-Board-Power-Supply-Module/272856322697?var=572011745827 , ebay

..... oooptions*

(*free will* is just another mental shill)

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Downunder35m

8 weeks ago

Most won't accept anything above 9.5V and struggled with anything below 8.2-8.5V.
But it wouldn't be a problem a problem to replace the battery with a fixed or adjustable voltage regulator set to 9V, just add a jack for the power cable.
Most obvious downside however is that you provide a common ground for your tester.
This can cause problems getting accurate readings or in severe cases damage the meter.
These things should only connect the probes to what is powered but should not be connected in other ways to the power.
Isolating everything is the first rule and you make it possible to break it when you use a cable connection to power your meter.

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la xerraDownunder35m

Reply 7 weeks ago

stupid question: what actually happens if the voltage drops below 8.2, or goes over 9.5? gracias

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verencela xerra

Reply 7 weeks ago

Full, short answer: Anything. De nada.

Longer answer:
- far below 8.2?
Should just not turn on. (May get hot, though - very unlikely)
- a bit below 8.2?
Optimal: may turn on, detect under voltage, inform you and shut down.
Good: may not turn on.
Bad: may turn on and show (slightly?) wrong measurements
Fatal: may self destruct (unlikely)
- a bit above 9.5?
Optimal: may turn on, detect over voltage, inform you and shut down.
Bad: may turn on and show (slightly?) wrong measurements
Fatal: may self destruct (a bit more likely)
- far above 9.5?
Well, the higher you go, the bigger the risk of self destruction.

What exactly happens depends on the circuit and the amount of work (and hardware) the designer put in to handle over/under voltage cases.

Anyway, a battery operated circuit should handle some supply voltage variations. Batteries' voltage drops over time anyway. So, you could try 10V with TWO diodes to drop them to around 8.6..8.8V (the drop depends on the current). If the voltage is to low, go with only one diode. Or start with 14V and use a 7809 voltage regulator.

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verenceDownunder35m

Reply 7 weeks ago

Good idea with the voltage regulator (like the good old 7809), just keep in mind that you have to account for the voltage drop accross them - like you have to feed in at least 12 or 14V - check data sheet.

For the common ground problem - yes that is something to keep in mind. But only, if you want to measure something in your supply circuit. I.e. the voltage reglator or the solar system - and even then only, if you have to connect the minus input (aka GND) to something that is not GND. A fast triggerig fuse may help here...

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la xerra

7 weeks ago

__yonatan24: ^I need to use one of these instead of a multimeter: DC-100V-10A-Voltmeter-Ammeter-Blue-Red-LED-Dual-Digital-Volt-Amp-Meter- Capitalism?...

__xerra: talking about price in+-sanity: you might like that: Yellow 22MM AC60-500V LED Voltmeter Voltage Meter Indicator Pilot Light New , Total: 1,25 EUR ....

that comes handy for me. i get about 300 w from the solar kit in the cabin here. sometimes i plug in some gadget that pulls more (esp the first spike at switching it on). i use some cheap-a$$ regulator (dimmer?) inbetween to bring down the voltage. but since that toy has no display built-in i´ll hook up above chinameter to see where i am at. danke.

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Jack A Lopez

8 weeks ago

You are correct in thinking a battery powered gizmo must have some range of supply voltage it can tolerate, and still work comfortably, happily, reliably... I am kind of searching for the right adverb there.

Usually lower voltages are more comfortable than higher ones. So if you have a choice between 8 and 10 volts, for a device powered by a "9 volt" battery, then 8 volts is probably the better choice.

By the way, there is a special caveat for battery powered multi-meters.

Most of those are incapable of measuring their own supply voltage, or voltages not isolated

https://en.wikipedia.org/wiki/Galvanic_isolation

from their own supply voltage.

So if you wanted to use the multimeter to measure the voltage of the battery of your solar kit, while powering the multimeter from that same battery, then that will be much more tricky.

I mean, try it and see what happens. I don't think this will break the multimeter. I think it will simply tell you a wildly incorrect voltage. If it does break your multimeter, then you are at a loss of like 10 USD, plus the trouble to get a new cheap multimeter. I don't know how far away from your mountain-cabin is the store from which you buy these meters.

By the way, there exist digital voltmeter modules, capable of measuring their own supply voltage, and probably the cheapest, best, place to get those, is from the Chinese eBay sellers who sell such things.

Although the trouble with those guys is the documentation is kind of sparse. Usually the best you will find is a list of specs written in comically broken English, and a wiring diagram, as one of the pictures in the eBay listing itself.

Actually, the best way to shop with those guys, is to be clairvoyant. That way you know what you're getting before you get it.
;-)

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la xerraJack A Lopez

Reply 7 weeks ago

thanks rabbit jack.
_a: leeway?
_b: no, the multimeter is not for checking the solar-kit (it has its own regulator w display) - its just for... how can i put it: go back to the childhood, & play around with and start blowing stuff up
_c: they throw mulitmeters at you at way below 10 bucks these days... gotta double-check, but the one i am gonna order costs about threefifty - its really all totally insane (example, since you ask about the cabin here in los picos de europa: i order online bolts for rock-climbing, one for 1 euro - i figure just to drive the delivery-truck the finally stretch from the ´main´-road up here to the village costs half of it ... not to mention that thing is shipped from china

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Jack A Lopezla xerra

Reply 7 weeks ago

Regarding the, what I am calling "comfortable" range of supply voltage, I don't know, but I would guess about {6 V, 12 V}.

You can do some testing yourself, if you have a DC power supply with variable output voltage, like one of these "lab bench" style power supplies, with a knob to turn to adjust the output voltage.

The low side of this range is safe to explore, since the meter has to be able to cope with a dying battery.

What happens at the lower supply voltages is, first the meter turns on its "low battery" indicator. At voltages lower than that, the meter's ability to measure things becomes skewed, especially if the voltage internal reference it is using for that drops lower than it should be.

At too high supply voltage, mostly what happens is the ICs (integrated circuits) run hotter; i.e with greater power dissipation. Turn the supply voltage up too high, and it gets more and more likely something will cook itself and burn out.

Actually there is another possibility for too high supply voltage. The designers might have thoughtful enough to build in some kind of protection against this condition, and there are various possibilities for this; .e.g. a special warning on the display, ICs intentionally shut down, etc.

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Yonatan24

7 weeks ago

Exactly what Petercd wrote. Keep in mind it can make the multimeter go a bit crazy. Did that, and if I was barefoot, the multimeter leads would shock me slightly.

I have a pretty simple idea for a tool I can make for measuring batteries, that's way more practical than using a multimeter. Been planning to make an I'ble about it for years.

I wanted to modify a multimeter to work on rechargeable 18650s so I wouldn't need to care about turning it off, but a buck converter consumes ~30mah passively. Multimeters are also very cheap (comparatively) on eBay and you might be able to get one that's powered by 2xAA batteries. I've killed 2 multimeters in the past few months because I go back and forth between settings... Need to make my own from a cheap volt/amp display.

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Yonatan24Yonatan24

Reply 7 weeks ago

3rd comment... I misread and thought you wanted to power it with a power supply. Still works I guess.

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petercd

8 weeks ago

You can run a 10V cell with a diode in series
(voltage drop of 0.7v), so essentially you'd be feeding the meter with
9.3v which will be cool and the gang.

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la xerrapetercd

Reply 7 weeks ago

thanks. as a boy i fukced around a bit with electronics - wanna get back into that in the home-stretch of live, closing the loop (aaall a loop).

need to brush up on kg-nowledge first. pulled an old tv out of the trash the other day. sure could salvage some diode that fits from it.... otherwise, well, see below: ch-ch-china again