Go Down

Topic: Batteries and current (Read 2593 times) previous topic - next topic

jamie297

Hi guys, been playing with the arduino for a while now but never had a strong electronics background so struggling now I'm trying to incorporate things that aren't powered directly off the arduino.

I've got a 12v car fan heater that is normally powered off the cigarette lighter. It's marked as 13 amps/150w, in my project I want the power to be self contained not off the car battery.

I've got 10 1.5v AA batteries in series which according to my multimeter produce somewhere between 13.5 - 16 volts depending on temperature etc. The thing is when I connect up the heater to my batteries they don't quite seem to be producing enough current to drive the fan at the same speed it does when in the vehicle. The thick wire from the heater is connected directly to the terminals on my battery pack so I can't see it being a problem with the thickness of the wire.

Any advice/suggestions on this would be most appreciated - as explained I'm only really starting out with electronics and unfortunately can't really seem to get the info I need for this from any off the beginner electronics videos.

JimboZA

Answers vary depending on where Mr Google takes you, but it seems certain that an AA battery will provide nowhere near 13A.... an order of magnitude less seems to be a general feeling, roundabout 1-2A.

There's nothing you can do about that fact of physics. So you need a better power source: I'm thinking the RC hobbyists here on the forum will have some idea. Those guys are clued in on the best way to deliver portable energy. Maybe a motor bike battery?

Johannesburg hams call me: ZS6JMB on Highveld rep 145.7875 (-600 & 88.5 tone)
Dr Perry Cox: "Help me to help you, help me to help you...."
Your answer may already be here: https://forum.arduino.cc/index.php?topic=384198.0

Peter_n

When you say: "they don't quite seem to be producing enough current", that is indeed the problem. But it is also a big understatement ;)
The AA batteries can supply 0.5A to 2A (it depends on the type and brand). The fan needs 13A !

Could you start with a small fan and a power supply ?
For example a switching power supply of 12V and 2A. And with a fan of 1A.
How do you want to switch the fan ? With a relay or a mosfet ?

Using 12V near an Arduino board could easily destroy the Arduino board. Keep wires with 12V away from the Arduino.

(while I was writing this, JimboZA wrote the same)

jamie297

Thanks for your responses Jimbo and Peter. I think I forgot that because the batteries are in a serial configuration the current doesn't increase like the voltage does! I'm about to go into an electronics store so am probably just going to purchase a small 12v battery.

And yes, the arduino will be protected by a regulator, the heater turned on by a transistor.

Peter_n

#4
Nov 22, 2014, 04:29 pm Last Edit: Nov 22, 2014, 04:29 pm by Peter_n
Did someone say batteries in series and 12V battery ? : http://www.youtube.com/watch?v=ZxBF7WC0TQk   :D

JimboZA

Did someone say batteries in series and 12V battery ? : http://www.youtube.com/watch?v=ZxBF7WC0TQk   :D
That guy's bat-crap-crazy. I haven't laughed so much in ages.
Johannesburg hams call me: ZS6JMB on Highveld rep 145.7875 (-600 & 88.5 tone)
Dr Perry Cox: "Help me to help you, help me to help you...."
Your answer may already be here: https://forum.arduino.cc/index.php?topic=384198.0

Robin2

#6
Nov 22, 2014, 08:19 pm Last Edit: Nov 23, 2014, 10:29 am by Robin2
probably just going to purchase a small 12v battery.
NO. Buy a BIG 12v battery.

Not only do you need a battery that is capable of producing 13 Amps without the voltage dropping. You ALSO need a battery that ca provide 13 amps continuously for some period of time. For example a 12v battery that is labeled 25 Amp-hrs capacity can probably provide power for 1 hour - because the capacities of batteries are usually grossly exaggerated.

If using a Lead-acid battery I would use at least a 100Ah battery if I wanted to draw 13 amps from it regularly. Nominally, when it says 100Ah that is what you get at a discharge rate of 5 amps over 20 hrs. You are drawing nearly 3 times that much. And 100Ah is the size of a car battery. And, a car starter battery will not be suitable for any long term use. They are only intended to power the starter motor for a few seconds before being recharged.

A fan that needs a lot less power might be indicated.

Edit to add ....
It was only after reading the next Post by @TomGeorge that I realized you are trying to run a heater from a battery. That is completely impractical.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

TomGeorge

Hi,can you please post a picture of your 150W fan heater.
Are you trying to make a portable electric heater.
If so, I think you will now find out why they aren't popular or around.


Tom..... :)
Everything runs on smoke, let the smoke out, it stops running....

JimboZA

Did someone say batteries in series and 12V battery ? : http://www.youtube.com/watch?v=ZxBF7WC0TQk   :D
That guy should team up with Dave Jones....
Johannesburg hams call me: ZS6JMB on Highveld rep 145.7875 (-600 & 88.5 tone)
Dr Perry Cox: "Help me to help you, help me to help you...."
Your answer may already be here: https://forum.arduino.cc/index.php?topic=384198.0

Mastrofski

#9
Nov 24, 2014, 04:23 pm Last Edit: Nov 24, 2014, 04:33 pm by Mastrofski
The biggest question you need to ask yourself when it comes to sourcing batteries is how long do you need this thing to run for? Your best bet would be to go with a Sealed Lead Acid battery (SLA). They're basically the same as car batteries, just smaller and usually a little less powerful.

A battery will typically have an AH rating(Ampere-Hour), the math is very straight forward. If you have a 12AH battery and you have a 12A draw, it will last for one hour. Likewise, a 1A draw will last for 12 hours.

If you only need it for one hour, I'd recommend this battery. Typically around $50, but they are hearty batteries. For roughly three hours of run time, I'd recommend this battery.  Anything more than that and you'll need to get a deep cycle, lead acid, battery(typically labeled as marine trolling motor batteries).

If you do end up buying a larger, lead acid battery, it is imperative that you buy one with deep cycling capabilities. If you don't, you'll kill the battery for reasons beyond the scope of this discussion.

For what it's worth, I worked at a battery store(Batteries Plus) for 4 years, so batteries(and making suggestions) tend to be my strong suit.

Hopefully I helped

-Matt

Edit:
If you let me know how long you intend to run this thing and how often you'd want to charge it, I could possibly make further suggestions.

Robin2

Your best bet would be to go with a Sealed Lead Acid battery (SLA). They're basically the same as car batteries, just smaller and usually a little less powerful.

A battery will typically have an AH rating(Ampere-Hour), the math is very straight forward. If you have a 12AH battery and you have a 12A draw, it will last for one hour. Likewise, a 1A draw will last for 12 hours.

If you only need it for one hour, I'd recommend this battery. Typically around $50, but they are hearty batteries. For roughly three hours of run time, I'd recommend this battery.  Anything more than that and you'll need to get a deep cycle, lead acid, battery(typically labeled as marine trolling motor batteries).

If you do end up buying a larger, lead acid battery, it is imperative that you buy one with deep cycling capabilities. If you don't, you'll kill the battery for reasons beyond the scope of this discussion.

For what it's worth, I worked at a battery store(Batteries Plus) for 4 years, so batteries(and making suggestions) tend to be my strong suit.
As I said earlier, in my opinion the Ah capacities of lead acid batteries are grossly exaggerated - perhaps twice what they really are.

I could not open your links to the batteries.

Starter batteries are specially designed to give a huge current for a few seconds until an engine starts. I presume you can get sealed starter batteries but they would not be suitable for sustained output or more than a few moderately deep discharges.

I use my un-sealed lead acid batteries 24/7.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

Mastrofski

As I said earlier, in my opinion the Ah capacities of lead acid batteries are grossly exaggerated - perhaps twice what they really are.

I could not open your links to the batteries.

Starter batteries are specially designed to give a huge current for a few seconds until an engine starts. I presume you can get sealed starter batteries but they would not be suitable for sustained output or more than a few moderately deep discharges.

I use my un-sealed lead acid batteries 24/7.

...R

Yeah like I said that's why it's super important to get a deep cycle battery, usually labeled as a Marine or RV battery. Lead Acid batteries are categorized as SLI(Starting, Lighting, and Ignition). They can then be broken down into two more categories, starter batteries and deep cycle batteries.

Your starter batteries that you mention, you are absolutely correct. They are designed to meet the current requirements of a starter, and then be charged right back up via an alternator or a stator. While some manufacturers do put an AH rating on the battery, you really should ignore that. They should have a CCA rating on it, which stands for Cold Cranking Amps. There's a relationship between CCA and true Amps the battery can deliver, which I cannot remember off the top of my head.

The reason they don't last as long in a deep discharge application is because of a process that we called sulphation. Basically, when a battery gets below 80% of it's charge, the sulphur in the sulphuric acid would begin to separate from the acid and form on the lead plates. The lead plates have holes in them for electron flow, and the sulphur buildup would start to restrict electron flow. The analogy that we liked to use was that it's similar to plaque buildup in arteries before somebody has a heart attack.

The reason that deep cycle batteries are required for this kind of application is two fold. Deep cycle batteries are built with thicker plates, to help negate the effects of sulphation. Secondly, the plates were coated in a solution that would slow down the actual effect of sulphation. Allowing the battery to be dropped below the 80% charge threshold. These batteries also sacrifice some of the CCA capabilities of their starter counterparts.

The sealed lead acids that I linked to(one was a 12V, 14AH VRLA, the other a 12V, 35AH VRLA) are what are known as AGM(absorbed glass matting). They have a fiberglass matting that soaks up the electrolyte and creates some benefits that way. Some people call them gel cells,those people are wrong, they are almost always AGM batteries(there are very few, very specific markets for true gel batteries). All AGM have some inherent properties of a deep cycle battery, and in fact the majority of their applications are for standby power(such as this), typically in exit lights, fish finders, powerwheels toys, and actually the two I listed are commonly used for mobility scooters for those with disabilities.

The starter batteries that you said will die after a few deep discharges?You're absolutely correct. It's the equivalent of leaving your headlights on over night multiple times. Very few car batteries will handle that(the ones that will are AGMs).

Again, this is all knowledge and experience I've gained after working for four years as a technician/salesman at a store that specialized in batteries.

MarkT

All lead acid batteries are ruined permanently by over-discharge, there's no magic cure
for this, they cannot handle it.  So unless you monitor battery voltage and isolate it
below about 10.5 or 11V you can easily trash the battery to a small fraction of its
as-new capacity.

All batteries have a capacity that reduces with age, temperature and number of charge/discharge cycles (and particularly the depth of discharge).  The nominal
capacity is usually that obtained from a new battery, freshly charged, at a particular
temperature and at a particular discharge rate.  Derating by a factor of 2 is a wise
move as has been pointed out.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

Go Up