I want to make a battery pack that can make 7.5V at 3.0A.

[daffy1234]

Update: I ended up trying the D batteries, but the power isnt enough. It's as if the screen is out of sync. The screen is really really shakey. Once it tries to read from the disk, it draws too much power and resets. Any other ideas? I'd really rather not get a lipo battery. Maybe a nicd battery. Where can I get a nicd battery? I tried googling it but I can't find a place that makes custom batteries.

 

[(*steve*)]

What does the voltage across your battery pack read under load?

 

[gorgon]

As far as I can see you have not said anything about how many hours you want to run your system on the battery pack?
Another point is how portable you want it to be?

TOK

 

[donkey]

just a query on this topic. do you want portability or not?
I see everyone except you saying portability.
there are many ways to make the ps1 portable or run of batteries, alot of them will run for a few seconds, some a few minutes, some a few hours.
then you have to worry about cost of batteries, or a way to recharge them.
If this is for camping or something similiar I could probably track down something for your car that'll plug into the cigarette lighter to provide power.

 

[daffy1234]

What does the voltage across your battery pack read under load?

I'm sorry. I currently have no way to test that. I'm fairly new to this level of electronics, and I don't have a voltmeter.

If it helps, I'm using 5 "Enercell" brand D batteries wired in series.

 

[daffy1234]

As far as I can see you have not said anything about how many hours you want to run your system on the battery pack?
Another point is how portable you want it to be?

TOK

I'd like it to run for...quite a while. If you need an exact time, lets say 4 hours.

 

[daffy1234]

just a query on this topic. do you want portability or not?
I see everyone except you saying portability.
there are many ways to make the ps1 portable or run of batteries, alot of them will run for a few seconds, some a few minutes, some a few hours.
then you have to worry about cost of batteries, or a way to recharge them.
If this is for camping or something similiar I could probably track down something for your car that'll plug into the cigarette lighter to provide power.

I have no specific need for this other then a challenge and learning the next step in electronics (I've already learned a lot thanks to you all ). I'd like it to run for 4 hours. And yes, I want it to be portable. I'd rather not make a cigarette lighter version of it's ac adapter, because that would take out the challenge of making it 100% portable.

Edit: Just thought of another reason for it...I'm bored

 

[gorgon]

If you use a 12V 7Ah SLA and a smal DC-DC switch mode converter generating 7.5V with a capacity of at least 3A. With a good efficiency rate, like >90-95% you should be good for 7-9+ hours max load.

To charge it you can use a cheap car battery charger.

This will not be pocket sized, but highly portable.

TOK

 

[daffy1234]

If you use a 12V 7Ah SLA and a smal DC-DC switch mode converter generating 7.5V with a capacity of at least 3A. With a good efficiency rate, like >90-95% you should be good for 7-9+ hours max load.

To charge it you can use a cheap car battery charger.

This will not be pocket sized, but highly portable.

TOK

By "12V 7Ah SLA" do you mean something like this? Click here.

And what do you mean by "small DC-DC switch mode converter"? Please explain it like you're explaining it to a 10 yr old.

 

[CocaCola]

If you use a 12V 7Ah SLA and a smal DC-DC switch mode converter generating 7.5V with a capacity of at least 3A. With a good efficiency rate, like >90-95% you should be good for 7-9+ hours max load.

Can you elaborate where you arrive at your 7-9+ hours of run? I'm just not seeing the math work out that way...

You need 7.5v @ 3 amps so you are using/require 22.5 Watts...

If you are using a 12v battery you will need to drain it at 1.9 Amps to source 22.5 Watts (no loss) that would drain the 7Ah battery in 3.68 hours in a perfect world... Factor in a 10% conversion loss and still perfect world drain of the battery and I see total run time of 3.33 hours... Realistically I would expect about 3 give or take, before you potentially damage the SLA battery due to excessive discharging...

 

[davenn]

By "12V 7Ah SLA" do you mean something like this? Click here.

And what do you mean by "small DC-DC switch mode converter"? Please explain it like you're explaining it to a 10 yr old.

yes thats the type of battery

DC-DC converter in this case a buck converter as its lowering the voltage from 12V to 7V
( a boost converter ups the voltage)

just google say.... 4 Amp DC - DC buck converter

Dave

 

[daffy1234]

yes thats the type of battery

DC-DC converter in this case a buck converter as its lowering the voltage from 12V to 7V
( a boost converter ups the voltage)

just google say.... 4 Amp DC - DC buck converter

Dave

Oh, I see now. And I agree with gorgon. That battery isn't by any means pocket sized

After the D cells didn't put out enough power, I'm trying to get a custom ni-cd battery that has 12 cells. 2 groups of 6 cells that are wired in parellel to double the battery life. Assuming that each cell gives 1.2V.

Anyone ever used this site? Click here. If so, is their service good or bad?

 

[daffy1234]

I just realized that in order to continue, I really need a voltmeter. I can probably get one monday.

 

[CocaCola]

After the D cells didn't put out enough power, I'm trying to get a custom ni-cd battery that has 12 cells. 2 groups of 6 cells that are wired in parellel to double the battery life. Assuming that each cell gives 1.2V.

I have to say with all the money you are spending trying to get this to work you might as well have invested in a Lipo pack from the get go, just my opinion...

 

[gorgon]

Can you elaborate where you arrive at your 7-9+ hours of run? I'm just not seeing the math work out that way...

You need 7.5v @ 3 amps so you are using/require 22.5 Watts...

If you are using a 12v battery you will need to drain it at 1.9 Amps to source 22.5 Watts (no loss) that would drain the 7Ah battery in 3.68 hours in a perfect world... Factor in a 10% conversion loss and still perfect world drain of the battery and I see total run time of 3.33 hours... Realistically I would expect about 3 give or take, before you potentially damage the SLA battery due to excessive discharging...

for some reason I used 1A as my reference, and you are of course correct.

This was a real brainfart.

With a 90% conversion efficiency the real number should be 3.33hours.


TOK

 

[daffy1234]

I have to say with all the money you are spending trying to get this to work you might as well have invested in a Lipo pack from the get go, just my opinion...

I'd really rather not go with lipo. I've seen what those things can do if used wrong.

 

[CocaCola]

I'd really rather not go with lipo. I've seen what those things can do if used wrong.

They are used in almost all consumer portable products now, phones, laptops, cameras and even cordless power tools... There is nothing arguably more dangerous about them vs other batteries as long as you use the proper charging tools...

 

[daffy1234]

They are used in almost all consumer portable products now, phones, laptops, cameras and even cordless power tools... There is nothing arguably more dangerous about them vs other batteries as long as you use the proper charging tools...

My fear is that this it just a prototype. I don't want to buy a lipo battery and end up discharging it too fast or charging it at the wrong voltage. There are so many windows of error with lipo batteries.

 

[CocaCola]

My fear is that this it just a prototype. I don't want to buy a lipo battery and end up discharging it too fast

As I explained previous, you are well within the discharge limits of even low discharge rate Lipos...

or charging it at the wrong voltage.

Not if you get the appropriate Lipo balance charger, they can be had on Ebay for $7...

There are so many windows of error with lipo batteries.

Only if you try to cut corners, or ignore the basics, and this applies to any battery choice you use...

If you insist on not using them, I'm afraid the only viable solution I see is a large (car battery sized) sealed lead acid battery, but beware that they can explode if not properly charged/used and will spray acid everywhere, so it's not carefree...

 

[daffy1234]

As I explained previous, you are well within the discharge limits of even low discharge rate Lipos...



Not if you get the appropriate Lipo balance charger, they can be had on Ebay for $7...



Only if you try to cut corners, or ignore the basics, and this applies to any battery choice you use...

If you insist on not using them, I'm afraid the only viable solution I see is a large (car battery sized) sealed lead acid battery, but beware that they can explode if not properly charged/used and will spray acid everywhere, so it's not carefree...

I'd rather go with a smaller lipo battery then a car battery sized battery labeled as "lead acid". I'll look into the lipo batteries then.