How would I figure out if a battery pack can supply enough current for a device? - Page 1
Forum section: electronics / beginners

author: eihli
author_rank: Newbie
timestamp: November 15, 2021, 01:52:58 am
content: I'm trying to build a thermal printer instant camera out of a CSN-A2 mini thermal printer and a raspberry pi.The printer says it can run on anywhere between 5v-9v or 12v.When I plug it into a 5v wall adapter, the "ink" is pretty light, like the print head isn't heating up enough to get a good solid burn. When I plug in with a 12v wall adapter, everything is perfect.Now, I want to make it portable. I thought using 8 1.5v AA batteries in series should work since that will be 12v. The paper moves, slowly, and there's practically zero burn.So obviously voltage isn't the only thing that matters. There's something about current. But the CSN-A2 data sheet only mentions the required voltage. It doesn't say anything about the required amperage. And the packaging on AA batteries only mentions voltage.How do I know 1) How many mAh can 8 AA batteries in series supply, and 2) How many mAh does the thermal printer draw from 12v wall plug?Thanks!

author: ledtester
author_rank: Super Contributor
timestamp: November 15, 2021, 02:03:06 am
content: When new alkaline batteries can deliver a lot of current -- like several amps. The problem is that as they deplete their internal resistance increases which causes them to "sag" more when you draw a lot of current from them.I think your best bet is to simply power the printer with a set of batteries, continuously run the printer and see how long the batteries last.The run time will depend on the brand of batteries you use -- the mAh rating of a battery depends on the manufacturer.QuoteWhat are the specs of the wall adaptors -- i.e. how much current can they deliver -- esp. the 12V one?

author: eihli
author_rank: Newbie
timestamp: November 15, 2021, 02:23:46 am
content: The 12v wall adapter that was working good was 12v 1.5A. I can't find the 5v charger to read its amperage.Could I measure how much the printer is actually drawing by connecting a multimeter in series, setting it to measure amps, and printing something? Is that the only typical way to know how many amps something draws if it's not on the data sheet? Or is there a way to calculate it with other info that is typically provided in a data sheet?Also, the AA batteries are brand no and don't work at all, not even for a second. (By "don't work", I mean the printer prints really slow and the burn is practically non-existent.)I read elsewhere that LiPo batteris are capable of providing more current and someone said Alkaline didn't work for a thermal printer camera they built but 5 volts of RC-car batteries did work.I guess I'm just really surprised that it's not advertised how many amp hours a battery can output. Like... if I didn't read on some a forum that Alkaline batteries didn't produce enough current, and if it's not on a battery data sheet, and the printer doesn't specify how many amp-hours it draws... How would I figure out what I need to know to get this working?

author: cortex_m0
author_rank: Regular Contributor
timestamp: November 15, 2021, 03:07:41 am
content: Most consumer grade products are intended for use with only the power brick the manufacturer provides, so the answer to that question: you aren't "supposed" to figure it out.Most Alkaline batteries from quality manufacturers have impedance data. The battery current changes over the discharge cycle. The amp-hours available also depends on the load current.https://data.energizer.com/pdfs/e91.pdf

author: BrokenYugo
author_rank: Super Contributor
timestamp: November 15, 2021, 03:29:36 am
content: Yes, you could measure the current with a multimeter as described, use the highest current range and ideally short heavy leads. Ideally you'll have a second meter measuring the voltage at the input to the device. On that note the simple test to see if the power supply and wiring is adequate is to just measure the voltage while it's operating and see if the voltage drops too much.Also, in the listing below, which appears to be fairly close to the actual source, it's listed as a 12V version and a 5-9V version, so it'd make sense it only heats up and works properly on 12V.https://www.aliexpress.com/item/1476158924.html

author: ledtester
author_rank: Super Contributor
timestamp: November 15, 2021, 03:44:09 am
content: Different battery brands have different capacities -- just look at these tests:Expensive Batteries vs Cheap Batteries! -- Frekin' Reviewshttps://youtu.be/RWAjgZmnoZoAA Alkaline Battery Capacity Test - Duracell, GP, Varta, Energizer, ... - Project Farmhttps://youtu.be/V7-ghrTqA44and as you use a battery its voltage will drop.Fresh alkaline batteries should be able to deliver 1.5A at least for a short period of time. Are you using brand-new batteries? As BrokenYugo mentioned, measure the voltage of the battery pack when current is being drawn from it -- that will tell how much voltage is actually getting to the printer.

author: brucehoult
author_rank: Super Contributor
timestamp: November 15, 2021, 03:46:32 am
content: They really do seem determined not to give an amps or watts rating!Adafruit recommends using a power supply capable of 2 A, 1.5 minimum.https://learn.adafruit.com/mini-thermal-receipt-printer/powerNiMH or Li-ion AAs can supply 0.5 A reasonably happily (without decreasing their total capacity by all that much). Alkaline's get their rated capacity at 25 mA, and at 0.5 A they have only about half the rated capacity.So I'd say if you want to use AA you will want 3 or 4 in parallel, times 6 or 8 in series, or 18 to 32 cells in the battery pack in total. And NiMH would be the best type to use.But you'd be much better off using D cells if you can. Then you'd only need 6 or 8 of them in series. They can supply 1.5 to 2 Amps no problem.

author: brucehoult
author_rank: Super Contributor
timestamp: November 15, 2021, 03:51:37 am
content: Quote from: eihli on November 15, 2021, 01:52:58 amExactly the same as the mAh one AA battery can supply. But at 12 V instead of 1.5 V.QuoteIt seem from the Adafruit page it's about 1500 times the number of hours it's turned on (printing?) for.

author: Rick Law
author_rank: Super Contributor
timestamp: November 15, 2021, 07:58:50 am
content: Adding to BruceHoult's point...For 12V 1.5A plus, with NiMH you will need 18 to 32 cells, which is a big number to handle. With LiIon, you could get away with 3 in series or 6 cells in 2p3s (2 parallel in 3 series). But building a 18650 type LiIon pack will require a bit of experience. Besides building the pack, you will also need to build a way of charging the pack. Building a LiIon pack (and a charging solution) is not a job for beginners. Done wrong, 3 LiIon cells in series carries enough energy to get you into serious problems up to and including the cells breaking out in flames.With the questions you were asking, I assume you are a beginner.The simplest solution I can think of is LiIon 14500 sized "self-charging" batteries - those with charger already build-in to the battery cell. I am thinking theNiteCore NL1475Ror similar. The cell is AA cell sized, the cell itself has a micro-usb socket to be charged via USB. No need to build chargers, just get 3 usb to micro-usb charging cable. You will need one of those battery holder that is 3xAA in series.Link to NiteCore battery spec page:https://charger.nitecore.com/product/nl1475rEDIT: adding thisIf you do use usb-charging NiteCore, don't charge them with single charger with 3xUSB outletswhile they are in the battery holder. a 3 USB outlets on the same charger will probably have all three USB share the same ground. If you plug the charge cables into the batteries while they are in the holder, you will be shorting at least two of them.Note also, this is version two. I removed my initial reply and rewrote it when I remember NiteCore makes a battery with build-in charger.

author: Nusa
author_rank: Super Contributor
timestamp: November 15, 2021, 01:41:02 pm
content: Quote from: brucehoult on November 15, 2021, 03:51:37 amYou're answering the question he asked, not the question he meant. Which merely highlights that the original poster doesn't understand the terminology he's using.mA = milliAmp = current being used right nowmAh = milliAmp-hour = a measurement of energy. In the case of an AA battery, it'll be the battery capacity while being discharged at a nominal value such as 50mA. If the discharge rate is higher, the useful battery mAh rating will be lower.Which means if have an AA battery rated at 1500mAh, a new battery will last for 1500mAh/50mA = 1500/50mAh/mA= approximately 30 hours of continuous operation. But battery capacity is load-dependent. If you ask for 1000mA from that same battery, you would get less than 1 hour from it. If you ask for much more than 1000mA from an AA, don't expect to get it, and if you do, not for long.Your experiment probably would have worked if you'd used D cells. Here's a spec sheet for Duracell D:https://media.digikey.com/pdf/Data%20Sheets/Duracell/MN1300.pdfThe chart says it can deliver 2000mA (2 Amps) for about 2 hours. If you only need 1500mA while printing, and it doesn't print constantly, then it'll last much longer...possibly for an entire roll of thermal paper.

author: rstofer
author_rank: Super Contributor
timestamp: November 15, 2021, 02:04:54 pm
content: I think I would consider 18650 batteries. Three in series will deliver 10.8 volts at some serious amperage. And they're rechargeable.https://www.18650batterystore.comFor the battery holder:https://www.amazon.com/Battery-Holder-Besmelody-Storage-3-Slot/dp/B07DMWY1TL

author: rstofer
author_rank: Super Contributor
timestamp: November 15, 2021, 02:20:35 pm
content: Sometimes you can find a datasheet for a battery. Attached is one for a Li AA battery that shows continuous discharge spec of 1.5 Amps. Note that this is NOT your everyday AA battery. Search Google for other datasheets.https://data.energizer.com/pdfs/lithiuml91l92_appman.pdf

author: Peabody
author_rank: Super Contributor
timestamp: November 15, 2021, 02:53:04 pm
content: Before measuring the current with your multimeter, check the maximum current your meter will handle. If it's 400mA or 500mA, trying to measure the current will probably blow the fuse on your meter. A safer way would be to insert a 1-ohm resistor, or 0.1-ohm, into the line, then measure the voltage drop across it. Ohm's law will tell you how much current is flowing.But if you're looking at needing 1A or more at 12V, that's a lot of power. Three 18650's in series is likely to be the most economical solution in the long run.

author: tooki
author_rank: Super Contributor
timestamp: November 15, 2021, 06:59:07 pm
content: Quote from: eihli on November 15, 2021, 01:52:58 amThis page has some interesting claims about the power requirements:https://www.dkia.at/en/node/129Furthermore, from the sticker on the unit shown in the photo, it looks to me as though this model is sold configured EITHER for 5-9V OR for 12V —not both at the same time!!!If yours is a 5-9V unit, then running it at 12V is risky, and according to the article might not even work. If it’s a 12V unit, then running it at 5-9V would be severely underpowering it.FYI, don’t say that thermal printers “burn” the paper. They do no such thing. Thermal paper is sensitive to fairly low temperatures (you can “write” on it by dragging a fingernail across it at high speed; the friction alone causes it to darken).

author: rstofer
author_rank: Super Contributor
timestamp: November 15, 2021, 08:59:38 pm
content: If the printer is like this:https://www.manualslib.com/manual/937853/Cashinotech-Csn-A2.html?page=4#manual-- Page 4Just 2 18650 would provide 7.2V, just between 5V and 9V spec'dTwo cell holder:https://www.amazon.com/Battery-Holder-Batteries-Envistia-Mall/dp/B07N56GQ95

author: eihli
author_rank: Newbie
timestamp: November 16, 2021, 05:12:14 am
content: Thank you all. This thread has become a treasure trove of information for me.I have some LiPo batteries on order, the rechargeable kind used in RC cars. I'm going to experiment with those. I also have 8 D batteries that I'll try.