Battery Thoughts

Hi all,

I realize this is a wide-open question, and it largely depends on individual project requirements, but what do you mostly consider when selecting a suitable battery for your project?

  1. Voltage?
  2. Capacity (mAh)?
  3. Chemistry (lipo, MiMH, alkaline etc)?

Also does anyone have experience of using a 'Power-brick' as a portable power source?

Useful knowledge for us new-comers to Arduino considering a battery for our projects.

badvoc: Hi all,

I realize this is a wide-open question, and it largely depends on individual project requirements, but what do you mostly consider when selecting a suitable battery for your project?

  1. Voltage?
  2. Capacity (mAh)?
  3. Chemistry (lipo, MiMH, alkaline etc)?

Also does anyone have experience of using a 'Power-brick' as a portable power source?

Useful knowledge for us new-comers to Arduino considering a battery for our projects.

All of the above in equal parts, plus cost, availability, recharge method, environment, safety, size, weight, discharge cycles expected etc.

I would like to see some form of guideline for battery choice posted, (and would happily contribute with information gained over 15 years of specifying Lead Acid solutions). There is so much misinformation and so many half truths about battery technologies and capabilities etc floating around that needs to be corrected.

  1. Voltage?

Yes. A "standard" Arudino (uno, etc.) runs from 5V, but there's a voltage regulator. The recommendation is 7V or more into the regulator, but you can usually get-away with 6V.

The higher voltage your battery is, the farther-down you can discharge it. For example, a 12V battery can go down to 7V (and it would be normally be considered "dead' or nearly-dead) but the Arduino would still be running fine with 5V out of the regulator.

On the other hand, the Arduino has a linear regular. That means it's inefficient and wasting power. The more voltage you "'drop" across the regulator, the more energy you are wasting. With a 12V battery, you are dropping 7V across the regulator and the regulator is burning more energy (and draining more battery power) than your main 5V circuitry.

And if you are powering additional circuitry from the Arduino's regulator, it can overheat. The more voltage you drop across the regulator, and the more current you draw through it, the hotter it gets. That heat is a direct result of wasted energy...

An external switching-regulator is nearly 100% efficient, almost no energy is wasted, and you'd get more battery life. The efficiency means you can get more current out regulator than is coming out of the battery (at a lower voltage). i.e. More hours from your milliamp-hours...

  1. Capacity (mAh)?

If you know how much current you're drawing, the mAh rating will help you estimate battery life.

  1. Chemistry (lipo, MiMH, alkaline etc)?

Of course, you need to decide if you want rechargeable batteries. Then, it's an issue of the type of charger you want to use, battery size, weight, mAh capacity, cost, etc. I wouldn't choose based on the "chemistry", but there may be a certain chemistry that best meets your specs/requirements.

Thanks all, very informative.

Good advise on the switching-regulator. I was considering the TS2940 voltage regulator for a project i was working on http://www.farnell.com/datasheets/50393.pdf as it has a low-voltage-dropout, seems far better than the standard 7800 type, but has a lower current limit.

Whilst experimenting i was able to supply 5v to the Arduino UNO direct to the VIN pin (with i believe uses the on-board reg), i don't need to drive any pin outputs so i guess this would be impossible otherwise, just an observation and interested to hear if anyone else has tried this?

I still think there is a potential to consider Lead Acid batteries for projects, i don't know much about portable options and possible weight implications, so if anyone has used this type of battery for a portable project i would be interested to hear how you got on.

LiPO batteries are used in mobile devices because of their high energy density and low weight, but they contain a flammable electrolyte and will burn your house down if improperly charged or mechanically damaged. 170+ LiPO fires http://www.rcgroups.com/forums/showpost.php?p=1936756&postcount=4 LiPO explosion https://www.youtube.com/watch?v=k9mcNvOGKtI LiPO fire https://www.youtube.com/watch?v=773yPtIsl-0

Some postal organisations prohibit the sending of LiPO batteries, or insist on road freight rather than air freight for safety reasons.

You can buy flameproof fibreglass charging bags http://www.towerhobbies.com/products/greatplanes/gpmp0751.html

LiFePO4 batteries have a slightly lower energy density but are less likely to catch fire. LiFePO4 puncture test https://www.youtube.com/watch?v=EMARDvMz62A

Given the advances in LiFePO4 battery technology it's a mystery as to why LiPO batteries are still allowed in consumer devices.

Power bricks - some have experienced the bricks shutting down when too little current is drawn.

If you're going to power the board with 5V, do it thru the USB connector, or direct to 5V on the power header.

LiPos are also good in flying vehicles.

CrossRoads: Power bricks - some have experienced the bricks shutting down when too little current is drawn.

So that explains why when I was trying to measure voltage and confirm polarity of a USB socket I kept losing voltage.

C - The current draw the battery is capable of.

LiPos can be well up to 50->100C (where the current draw = capacity in Ah * C). If you try and pull a few Amps from a 9V NiMH...you may be in for a very warm battery and potential fire. Manufacturers tend to be on the safe side, but some AA NiMH will be around 10C maximum...2C on the manufacturers "reccomendation".

It seems hard to find any real documentation on the "current draw limits"...but 5C for a 2.2Ah = 10Amps from a NimH AA battery. Not bad like, having a 12V pack of them means you can draw 10Amps = P=IV = 120W.

Again, if this were a quadcopter, an electric motor/robot with more than 120W power use...expect some exploding hot AA batteries.

A LiPo would be the best option for power.

Johnny010:
C - The current draw the battery is capable of.

LiPos can be well up to 50->100C (where the current draw = capacity in Ah * C).

Sorry Johnny but I believe you are mistaken, there are 2 “C” figures used with batteries, a C prefix refers to rate of discharge and a C suffix refers to rate of charge.
To use your NimH example 5C would mean that the battery will accept 5 X 2.2amps = 11amps recharge current.

C5 would be the amp hour capacity, at the 5 hour rate would mean that the battery will supply 440ma for 5 hours.

In the industrial/commercial sectors the Cx rate determines which battery is selected (Off Grid Solar often uses the C100 rate, UPS equipment is often C20.) while the xC charge rate determines the size charger we supply and is normally matched to the applicable standards, for instance Emergency lighting requires the battery to be recharged in 16 hours where as often the Utility market specify 10 or even 6 hour recovery.

Johnny010:
It seems hard to find any real documentation on the “current draw limits”…but 5C for a 2.2Ah = 10Amps from a NimH AA battery. Not bad like, having a 12V pack of them means you can draw 10Amps = P=IV = 120W.

Again I must disagree, battery cells connected in series increase voltage not current, to increase current connect in parallel.

1 x 2.2ah battery (assumes C1 rate 2.2 amps for 1 hour) @ a nominal 1.2 volts (1.2 VPC) = 2.64 watts.

10 X 2.2ah cells connected in series @ 1.2VPC = 26.4 watts

P= I*V = 2.2a * 12v = 26.4 watts,
I = P/V = 26.4w / 12v = 2.2amps.

Kiwi_Bloke:
Sorry Johnny but I believe you are mistaken, there are 2 “C” figures used with batteries, a C prefix refers to rate of discharge and a C suffix refers to rate of charge.
To use your NimH example 5C would mean that the battery will accept 5 X 2.2amps = 11amps recharge current.

C5 would be the amp hour capacity, at the 5 hour rate would mean that the battery will supply 440ma for 5 hours.

In the industrial/commercial sectors the Cx rate determines which battery is selected (Off Grid Solar often uses the C100 rate, UPS equipment is often C20.) while the xC charge rate determines the size charger we supply and is normally matched to the applicable standards, for instance Emergency lighting requires the battery to be recharged in 16 hours where as often the Utility market specify 10 or even 6 hour recovery.

Again I must disagree, battery cells connected in series increase voltage not current, to increase current connect in parallel.

1 x 2.2ah battery (assumes C1 rate 2.2 amps for 1 hour) @ a nominal 1.2 volts (1.2 VPC) = 2.64 watts.

10 X 2.2ah cells connected in series @ 1.2VPC = 26.4 watts

P= I*V = 2.2a * 12v = 26.4 watts,
I = P/V = 26.4w / 12v = 2.2amps.

Urgh. I read something one place and it is contradicted in another. Yours males more sense to me.

Even though, I am sure some manufacturers have a C charge rate and also some state a C rate for “safe discharge”. From what I read that part made sense to me. Putting a paperclip across a 9V nimh for example…shorting a lipo with low resistance wire etc.

Johnny010: Even though, I am sure some manufacturers have a C charge rate and also some state a C rate for "safe discharge". From what I read that part made sense to me.

Most battery manufacturers have both a Capacity and a Charge rating.