Batteries question

A

adamg

Member
I have 24 AXE023's all needing battery power.

Instead of rigging them all up to individual battery packs, I would like to use one battery pack if possible.

Two motors are rigged up to each board, so 48 motors. Only one motor will be used at any one time on each of the AXE023. So the possibility of 24 motors running at the same time.

Would this battery pack be suitable?

http://www.batteryspace.com/nimhbatterypack36v13ah3xfforev.aspx

Or would it fry everything? I am a total beginner - so don't really understand much about the amps etc. But here is what I figure:

1) each motor can draw up to 1/2 an amp- so I need around 12 amps

2) the battery pack seems to be 13 amps. Therefore it should be powerful enough.

3) Because the voltage is correct (3.6v) it won't catch on fire, because electronics only draw the amps they need? (Or am I very wrong?)

It has to be a fairly light battery and plugging it into anything else is not an option.


Thanks in advance for your help! :D
 
Buzby

Buzby

Senior Member
Hi Adam,

You need a few more calculations before you choose the right battery.

How long does the device need to be powered for, is it hours or minutes ?.

Are there always 12 motors powered, or are there significant 'dead times' when no motor is powered ?

Understanding your power requirements in detail will stop you spending too much on bigger than needed battery, or not enough on a too small battery.

Cheers,

Buzby
 
R

rossko57

Senior Member
adamg said:
1) each motor can draw up to 1/2 an amp- so I need around 12 amps
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That's a good assessment. Both of the packs so far will deal with that - this is the maximum "Discharge Rate".

The xxAh is the specs is a measure of capacity - the amount of water in the bucket. The battery can in theory provide XX Amps for 1 hour.
So for you, a 13Ah battery will last an hour or so with 12 motors working continuously. Or two hours if the _average_ current is 6.5A, with the motor circuits idle half the time.

Or you could use a smaller 5 or 6Ah battery for a half hour continuous activity... so long as the battery discharge rate is still > 12A

adamg said:
I don't like it when they say "May explode" in a warning!
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The full text is "Batteries may explode if charged or discharged improperly..." and then goes on to point out a couple of hazards. Most batteries in this class are quite capable of starting fires etc. but all can be used safely _if_ you follow the rules.
You have homework to do, and safety features to build into your design.
At the most basic for example, you'll want to fuse the battery feed to protect against a fire starting short-circuit somewhere in your mobile ratsnest of wires and motors.
 
S

srnet

Senior Member
Lets see;

2 x 3.7v LIPO Battery4rc 5800mAh = 11600mAh = £36.00

1 x 3.6v NiMH Battery Pack = 13000mAh = £30.18

NiMh expensive ?
 
B

BeanieBots

Moderator
Concur with srnet.
LiPo is great if you have a weight or volume problem but they are NOT the cheapest, Lead Acid is, with NiMh close behind.
You also need to consider maximum discharge depth of whatever technology you choose.
LiPo does not like to be discharged very deep and can explode if taken very close to empty.
NiMh is far more tollerant of abuse.
Once you've worked out the REQUIRED capacity, I would suggest getting a pack with TWICE that capacity so that they last a reasonable amount of charge/discharge cycles. Doubling the capacity will give more than twice the life so is likely to be cheaper in the long run assuming the device life is expected to be greater than a few hundred cycles.
 
L

lewisg

Senior Member
adamg said:
because electronics only draw the amps they need?
Click to expand...
Basically correct.

In the event basically correct fails that is why you need a fuse. In this case I'd likely fuse and wire for 15A. That means a 15A fuse as close a practical to the battery positive terminal and 14 AWG wire for hookup.


rossko57 said:
The xxAh is the specs is a measure of capacity - the amount of water in the bucket. The battery can in theory provide XX Amps for 1 hour.
Click to expand...
Heavy on the in theory part...

Many batteries will specify a rate for which the Ah spec is valid. In many cases this is something like a 20 hour rate. In real life very few batteries can deliver their Ah rating for 1 hour and even fewer can deliver 2x Ah for 30 minutes.


g6ejd said:
What you need is a battery designed for the modelling market - boats, cars and aircraft.
Click to expand...
Since we don't yet know the application that is a rash statement.

g6ejd said:
I would never buy a NiHm as they are low capacity, unreliable and expensive, LiPo is the way forward.
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Ummm, not really. LiPo's are best thought of as a transition technology. There will be better and more stable chemistries in the future. Unless you need a low weight to power ratio, high discharge currents and quick charging NiMh is likely a better choice.


BeanieBots said:
Concur with srnet.
Click to expand...
Same here!

BeanieBots said:
Once you've worked out the REQUIRED capacity, I would suggest getting a pack with TWICE that capacity so that they last a reasonable amount of charge/discharge cycles. Doubling the capacity will give more than twice the life so is likely to be cheaper in the long run assuming the device life is expected to be greater than a few hundred cycles.
Click to expand...
I have found this to be VERY true in the many years I have used many types of rechargable batteries. better to plan for 50% and in emergencies go to 80% then kill packs by over discharging them.
 
JimPerry

JimPerry

Senior Member
24 boards and 48 motors will present a challenge in wiring from 1 battery... unless you used a star-based power distribution the chances are that towards the end of your chain of 24 you will get multiple random power-related problems. :confused:

What physical layout will you have? How/are the boards connected except by power?

What will the motors do?
 
M

manuka

Senior Member
Adamg: Aside from clarifying " It has to be a fairly light battery and plugging it into anything else is not an option" ,best you also specify your budget & recharging considerations. Li-ion/Li-poly (3.6-3.7V per cell) or LiFePO4 (3.2V per cell) types are the lightest weight, but they demand smart charging & monitoring.

Factor in wiring,battery holder & connection issues as well-NiCd/NiMH types are only 1.2V a cell so quite a swag will be needed to give a decent voltage. This naturally means more scope for short circuits,poor connections or suspect cell(s). Just 3 x 3.6V series Li-ions will give 10.8V, while 9 x 1.2V NiCd/NiMH (along with the attendant wiring) would be required. Other things being equal fewer cells = fewer (boring) problems!

Footnote for trials (& skinflints): Globally standardised rechargeable spill proof 12V SLA (Sealed Lead Acid) batteries are often available cheap/free from security firms! Concerns about possible early failure mean they're replaced every 2-3 years in critical applications - diamond displays perhaps?!

The SLA battery Ah (Amp Hour) capacities usually range from 1.2 Ah to 7Ah - the latter are about the size of a 1kg block of cheese. Although heavy (& hence best suiting fixed applications),they're usually good for another 5 years use -marvellous for cash strapped hobbyists, schools & off grid applications etc.
 
L

lewisg

Senior Member
manuka said:
Globally standardised rechargeable spill proof 12V SLA (Sealed Lead Acid) batteries are often available cheap/free from security firms! Concerns about possible early failure mean they're replaced every 2-3 years in critical applications ... they're usually good for another 5 years use ...
Click to expand...
I deal in hundreds of 12v 7Ah SLA batteries mostly in UPS service but some in security panels. After 3 years most are at best 50% capacity which is fine if you only need 3Ah and nothing critical depends on it.

At least in the US free for these is ending since most times recyclers will pay if you have at least 100 pounds of them.
 
M

MikeAusP

Member
If you use LiPO or LiIon and you don't use a Protection Circuit Module that stops discharge when ANY cell drops below 2.5 volt, it can be very expensive.

At the best a) the cell will be permanently damaged and won't hold charge, at worst b) it will catch fire next time you charge it. So far I've only experienced a), but I now always use PCMs.
 
S

srnet

Senior Member
MikeAusP said:
If you use LiPO or LiIon and you don't use a Protection Circuit Module that stops discharge when ANY cell drops below 2.5 volt, it can be very expensive.

At the best a) the cell will be permanently damaged and won't hold charge, at worst b) it will catch fire next time you charge it. So far I've only experienced a), but I now always use PCMs.
Click to expand...
I have had b) happen 4 times.

Once the plane the battery was in fell out of the sky landed in the sea, and it stopped smoking.

Another time was over the park, the plane landed OK and the battery just swelled and smoked a lot.

A third time a battery caught fire on charge and almost burnt down my workshop.

A fourth time a small 1500mah battery exploded in a largish fireball a minute or so after I threw it out of the workshop.

I have used NiCd and NiMh batteries for many years, never had a problem.
 
G

g6ejd

Senior Member
The vast majority of modellers worlds wide use LiPo and correctly charged and discharged they are proving to be ultra-reliable. I have never seen a modeller had a battery catch fire. You would know if a failure was imminent, certainly before a flight as the battery would have swollen to huge proportions.

It's now very rare to find a supplier with Nimhs in stock - LiPo's a plenty though.

yes LiPo's need to be managed, but if done within their specification are great. I'm on flight 221 from an Overlander 11.1Volt (3S) 2200mAHr battery and it's like new, holds full capacity easily. Saved me a fortune in fuel.
 
M

manuka

Senior Member
LiPo powered flyins are now FAR quieter too-such "flying chainsaw" events were once irritatingly noisy!
 
G

g6ejd

Senior Member
Could not agree more, flight is now to all intents and purposes silent, which prevents complaints = good
 
M

manuka

Senior Member
Yes-but perhaps too quiet for purists. Check model planes that offer electronic "engine noises" & simulated guns (c/w LED firing effects) etc. On board Benedini sound modules can make model plane fly bys suitably spine tingling/unnerving as they pass overhead, & can be almost as convincing as the real thing.
 
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