# Homemade battery packs 48volts

is it safe to wire like 4 turnigy 11volt 2200mah 25c lithium polymer batteries in series and 4 in parrell using dean connectors? The reason I am asking is becuase I see some battery packs online that are expensive for the power they output. If lithium polymer is unsafe is it safe to use smaller lithium ion cells to make like a 48v 8800mah volt battery pack? I can get lithium ion cells pretty easily from laptop batteries.

## Answers and Replies

berkeman
Mentor
is it safe to wire like 4 turnigy 11volt 2200mah 25c lithium polymer batteries in series and 4 in parrell using dean connectors? The reason I am asking is becuase I see some battery packs online that are expensive for the power they output. If lithium polymer is unsafe is it safe to use smaller lithium ion cells to make like a 48v 8800mah volt battery pack? I can get lithium ion cells pretty easily from laptop batteries.

First of all, don't be wiring batteries in parallel unless you know a *lot* more about batteries.

Second, why do you want to use Lithium? Can you just use lead-acid batteries like car batteries to make the 4x12V=48V? Or even gel cell 12V batteries... What are you wanting to power? How are you going to recharge them?

lonely_nucleus
First of all, don't be wiring batteries in parallel unless you know a *lot* more about batteries.

Second, why do you want to use Lithium? Can you just use lead-acid batteries like car batteries to make the 4x12V=48V? Or even gel cell 12V batteries... What are you wanting to power? How are you going to recharge them?

There are many applications to having like 422,400 watts of power friend. I like to do experiments and engineering projects that require a lot of power, for example maybe I want to power a turnigy 80cc motor.

Lead Acid batteries are bulky and heavy, I want a battery pack that weighs more around 10 pounds or less. I have not used gel cell before so I am looking into it.

Recharging the battery pack should not be too much of a problem, I can use a lab power supply like this http://www.ebay.com/itm/30V-5A-Dual...980?pt=LH_DefaultDomain_0&hash=item541c51d57c
although the thing about recharging batteries is that the charger should have about the same voltage as the battery but the amp/hour from the power supply only affects the time it will take for the battery to reach the power supply voltage with that being said you do not want a charger that has more amp/hour than the battery.

What would you do if you wanted to make like a 30-48 volt battery friend?

berkeman
Mentor
2200mah

422,400 watts

I'm going to assume that you are using the European convention for the decimal point, and your power is 422W. 422W at 48V and 2.2Ahr give about 15 minutes of battery life. Not so great...

I would use four 12V gel cell batteries to make the 48V. Choose a type that is small enough that it comes close to your weight goal (are you wanting it to be portable?), and has an Amp-Hour rating that gives you better battery life. I would go for the "deep cycle" type if you can.

lonely_nucleus
I'm going to assume that you are using the European convention for the decimal point, and your power is 422W. 422W at 48V and 2.2Ahr give about 15 minutes of battery life. Not so great...

I would use four 12V gel cell batteries to make the 48V. Choose a type that is small enough that it comes close to your weight goal (are you wanting it to be portable?), and has an Amp-Hour rating that gives you better battery life. I would go for the "deep cycle" type if you can.
Thank you for the correction friend, I was doing quick calculations in my head should have done all the unit conversion on paper.

Gel cell batteries are expensive but they are nice. I would want around 4 of them costing something like 4*150=$600 gee wiz! Do you know if they are rechargeable and how much does a typical unit weigh? I am planning on making the project portable. I caddy during the summer so I can afford$600 on a battery pack that has so much power but I was looking to spend more around $150-200. Do you have any other cheap alternatives batteries if the weight limit is about 20 pounds? berkeman Mentor Thank you for the correction friend, I was doing quick calculations in my head should have done all the unit conversion on paper. Gel cell batteries are expensive but they are nice. I would want around 4 of them costing something like 4*150=$600 gee wiz! Do you know if they are rechargeable and how much does a typical unit weigh?

I am planning on making the project portable. I caddy during the summer so I can afford $600 on a battery pack that has so much power but I was looking to spend more around$150-200. Do you have any other cheap alternatives batteries if the weight limit is about 20 pounds?

Another alternative (probably better) is to use a single 12V battery and a "Boost" circuit to make the 48V for you. Boosting 12V to 48V is pretty common, so you should be able to find an off-the-shelf unit. That way you can use a single 12V gell cell battery. Can you say what the application is, and what kind of current you will need for how long from the 48V source?

lonely_nucleus
Another alternative (probably better) is to use a single 12V battery and a "Boost" circuit to make the 48V for you. Boosting 12V to 48V is pretty common, so you should be able to find an off-the-shelf unit. That way you can use a single 12V gell cell battery. Can you say what the application is, and what kind of current you will need for how long from the 48V source?

The machine should not draw more than 100 amps; I know I will need a high rated pulse modulating speed controller for that much amperage. I would expect the machine to last around a 15 minutes so I would need a battery that has around 25amp/hour. I could use the battery in my lab when I need it. No further information will be revealed about my summer engineerng project/science fair project, maybe I will say what it is later.

I never heard of boost circuits untill now, I am going to dedicate some research to them when I can.
Thank you for the possible battery sources friend.

berkeman
Mentor
100 Amps! Holy cow. That's a lot of power. 100A * 48V = 4.8kW. I hope you have a *big* circuit breaker in series with that power supply output.

BTW, battery energy capacity in Amp * Hours is generally rated at a set output current. For example, if you have a 10Ahr battery, that 10Ahr capacity is usually when you are drawing 10A for 1 hour. If you draw 20A, it will last for less than 30 minutes. There are discharge curves in most battery datasheets. Also, if you draw a high current from a battery, it can overheat and potentially burst. That's a bad thing, as you can imagine...

lonely_nucleus
100 Amps! Holy cow. That's a lot of power. 100A * 48V = 4.8kW. I hope you have a *big* circuit breaker in series with that power supply output.

BTW, battery energy capacity in Amp * Hours is generally rated at a set output current. For example, if you have a 10Ahr battery, that 10Ahr capacity is usually when you are drawing 10A for 1 hour. If you draw 20A, it will last for less than 30 minutes. There are discharge curves in most battery datasheets. Also, if you draw a high current from a battery, it can overheat and potentially burst. That's a bad thing, as you can imagine...
thank you for the discharge burst tip, I have never seen a battery burst surpisingly but what factor of the battery amp/hour does the load have to draw to cause a general battery to burst? *

I see that you are a ham, I will have to contact you sometime during the summer ok? Do you make your own antennas? I am getting my license this summer but I recently finished reading the AARL licencse manual and am currently reading AARL understanding basic electronics, 2 great books.

berkeman
Mentor
Do you make your own antennas?

Good for you getting your license! I mostly use the 2meter and 70cm bands for local disaster preparation type communication. And I help out at large public events (like bike rides and long runs) with communication using HAM radios. I've made some simple antennas, but mostly I buy mine. I have some friends who love making all kinds of unusual antennas to use with their equipment.

Good for you getting your license! I mostly use the 2meter and 70cm bands for local disaster preparation type communication. And I help out at large public events (like bike rides and long runs) with communication using HAM radios. I've made some simple antennas, but mostly I buy mine. I have some friends who love making all kinds of unusual antennas to use with their equipment.
Must be a fun hobby to help the community using sciene. Thank you for doing emergency services volunteer work. Some day I will do the same.

There are some very attractive antennas like the dish antennas, too bad a technical licence cannot operate on Ghz freqencies or can they?

rbelli1
Gold Member
Another reason for a circuit breaker is that in a fault mode any battery that can put out 100A for 15 minutes will probably put out several thousand for long enough to vaporize all of the conductors in your setup. Along with any body parts that may be in proximity.

Be sure that your circuit breaker or fuse is DC rated and capable of opening under any possible faults you can even remotely think of.

Be safe

BoB

berkeman
jim hardy
Gold Member
Dearly Missed
might four of these do ?

http://[URL='http://www.mkbattery.com/images/ES2_9-12.pdf']www.mkbattery.com/images/ES2_9-12.pdf[/URL] [Broken]

cheap enough to try, weigh ~3 pounds apiece, they'll do 100 amps for 5 sec 58 amps for 30 sec and only cost around fifteen bucks,.

Last edited by a moderator:
lonely_nucleus
might four of these do ?

http://[URL='http://www.mkbattery.com/images/ES2_9-12.pdf']www.mkbattery.com/images/ES2_9-12.pdf[/URL] [Broken]

cheap enough to try, weigh ~3 pounds apiece, they'll do 100 amps for 5 sec 58 amps for 30 sec and only cost around fifteen bucks,.
Thank you for letting me know about those batteries, do you know how many ma/h each battery is? I know that maximum dishcarge from a battery=c*amp/hours=>amp/hours=maximum discharge continuously/C rating, do we have enough information to calculate the mah of battery?

Last edited by a moderator:
jim hardy
Gold Member
Dearly Missed
nominal 2900,

that link is the spec sheet. did you take a look ?

Nominal Capacity
20 hour rate ( 0.145A to 10.50V ) 2.9Ah

10 hour rate ( 0.29A to 10.50V ) 2.755Ah

5 hour rate ( 0.493A to 10.20V ) 2.465Ah

1C ( 2.9A to 9.60V ) 1.305Ah

3C ( 8.7A to 9.60V ) 1.01Ah

nominal 2900,

that link is the spec sheet. did you take a look ?
Yes, I took a look at the page earlier. Do you know the difference between 20hour rate at 2.9Ah vs 10 hour rate 2.755Ah> Take it look at this sexy battery http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=26787 [Broken] it can output 260amps constantly and 540 amps in bursts! I could absorb all of its Electrical potential energy

Last edited by a moderator:
jim hardy
Gold Member
Dearly Missed
Yes, I took a look at the page earlier. Do you know the difference between 20hour rate at 2.9Ah vs 10 hour rate 2.755Ah>

You might spend some time here
http://batteryuniversity.com/
to get some vocabulary.

The faster you discharge a battery the less of its capacity you'll be able to use.
Basically there's ion migration happening in the electrolyte and that takes some time.

That battery you referenced is made for high discharge rates, gel cells are not.

Wow - 44 volts? Couple hundred amps? That thing's dangerous !

be careful. Look up "lithium battery fires" .

old jim

berkeman
You might spend some time here
http://batteryuniversity.com/
to get some vocabulary.

The faster you discharge a battery the less of its capacity you'll be able to use.
Basically there's ion migration happening in the electrolyte and that takes some time.

That battery you referenced is made for high discharge rates, gel cells are not.

Wow - 44 volts? Couple hundred amps? That thing's dangerous !

be careful. Look up "lithium battery fires" .

old jim
Thank you for the link Mr.Hardy. Gee wiz there is a lot of content to be covered at that website, have you read every single article there?

jim hardy
Gold Member
Dearly Missed
have you read every single article there?
not by a long shot.

But it's good to learn as much as you can absorb about every hobby you undertake....

i've not played with these modern high energy density batteries.
Once i put an A size lithium cell in my pocket. I'd found it in a dead piece of electrical equipment after a hurricane. It got across my car keys and darn near set my pants afire - I decided to leave those things alone until i had a need for them.

So be careful. That battery could make a flash like an arc welder that'd last several seconds and hurt you.
I dont know if it's the type prone to burn. Look at youtubes of lithium battery fires.

They've brought down airplanes so the danger is real.

https://gigaom.com/2011/04/04/lithium-ion-batteries-faulted-for-jet-crash/

A http://www.gcaa.gov.ae/en/ePublication/admin/iradmin/Lists/Incidents%20Investigation%20Reports/Attachments/16/2010-GCAA%20Accident%20Preliminary%20Report%20B747%20DXB%20.pdf [Broken] on the fatal crash of a UPS jet carrying a large shipment of rechargeable lithium batteries suggests that safety issues still remain for transporting these flammable devices, which are used to store energy not only for mobile phones and laptops but also a growing fleet of plug-in vehicles.

The crash, which killed both pilots, occurred near Dubai on September 3, 2010.

One hopes anything sold to the public would be pretty safe, but any concentrated energy source demands respect.

so be aware of what you have there. Read up on lithium battery safety
http://www.nrel.gov/education/pdfs/lithium-ion_battery_safety_hazards.pdf

and battery university
http://batteryuniversity.com/learn/article/lithium_ion_safety_concerns

Have fun , just be aware of "energy density" .

Last edited by a moderator:
CWatters
Homework Helper
Gold Member
Can I suggest the OP posts the question on one of the Electric Model aircraft forums. They have a lot of experience wiring Li cells in parallel and series. Search out people into the F5B competition class. The F5B Entry level class involves currents in the 300A range. The FAI F5B Open class is 300-400A ?

You should definitely NOT use a bench supply to charge Li cells - unless you want a fire!

F5B models are quite hard to video as they go like stink..

Last edited:
Can I suggest the OP posts the question on one of the Electric Model aircraft forums. They have a lot of experience wiring Li cells in parallel and series. Search out people into the F5B competition class. The F5B Entry level class involves currents in the 300A range. The FAI F5B Open class is 300-400A ?

You should definitely NOT use a bench supply to charge Li cells - unless you want a fire!

F5B models are quite hard to video as they go like stink..

Thank you. I actually got most of my knowledge of batteries from RC planes, I build them from scratch but buy all of the electornics . Are you sure that they involve currents as high as 300 amps? the biggest motor I have found at hobbyking is the turnigy 80CC 48 volt motor and it does not draw more than 150 amps, it outputs about 40 pounds of dry thrust. Can you give me an example of an rc plane that draws 300 amps of current because I have not seen a speed controller rated for that current.

Thank you for showing me that plane in the video, I was looking for a fpv long range sailplane.

i've not played with these modern high energy density batteries.
Once i put an A size lithium cell in my pocket. I'd found it in a dead piece of electrical equipment after a hurricane. It got across my car keys and darn near set my pants afire - I decided to leave those things alone until i had a need for them.

.
You put a lithium polymere battery in your pocket , ridiculous! well they certainly can be dangerous.
Thanks for letting me know not to but lithium polymere batteries in my pocket

CWatters
Homework Helper
Gold Member
F5B kit will do 300 amps but it's all optimised for burst running because of the nature of the F5B event. If you ran them for more than say 6 seconds at a time the aircraft is likely to be out of sight upwards or exceeding VNE!

When I flew F5B some years ago the two main companies for F5B competition motors were Kontronic in Europe and Aveox in the USA. Kontronic also made speed controllers. Competition motors weren't really available in shops. Usually got them direct of from reps at competitions. Some were special order only.

The same companies make motors for continuous running (eg scale models) but I'm not familiar with their latest range. Sounds like you might need a custom motor and controller.

Kontronic
http://www.kontronik.com
Aveox
http://www.aveox.com/
Nidec
http://www.nidec.com/
http://www.nidec.com/en-NA/technology/capability/f5b/

jim hardy
Gold Member
Dearly Missed
ridiculous! well they certainly can be dangerous.
Thanks for letting me know not to but lithium polymere batteries in my pocket

i'm glad you are familiar with them.

Have you ever done any arc welding? 100 amps at 25 volts will weld 1/4 inch steel plate.

I wasn't familiar with the batteries
if you're not familiar with high current - just wanted to warn you. i dont know your background.