HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Feb 25, 2011, 02:42 PM
Only flies cheap
Florida
Joined Jan 2007
169 Posts
Idea
Need advice for a project: Using RC battery gear for an extended life PSP Go

I know it's risky, but I'm looking for advice from fellow risk-takers. Spare me the usual lipo explosion warning unless you are willing to explain exactly the events that will certainly lead to catastrophe (in terms of the flow of electricity where it doesn't belong).

Sorry if this is too far off-topic, but I've been unimpressed by battery advice elsewhere - especially from video game people, who are usually clueless.

OK, so I bought a used PSP Go. Even when new, this thing doesn't have the greatest battery life (optimistically claimed 3-6 hours), and this one is performing worse than that. Unfortunately the battery is internal and swapping on-the-go isn't practical.

The battery inside the PSP Go is a 930mah 3.7v lithium ion (at least that what is says on the label, which you can see several pictures of here)

My basic idea is to add a connector to the case to allow me to connect an RC-style battery in parallel with the stock battery. I was hoping some of you battery experts could help steer me in the right direction and make this project successful.

Specifically I thought that using a hard case 1S lipo velcroed to the back of the PSP, and connected with magnetic terminals (ala Snap-N-Fly) fastened to the back of the case would be a good combination of simplicity and convenience, without significantly increasing the size & pocketability of the PSP when the external battery is not connected.

Some information that may be useful:
- It has built in circuitry to prevent over charging and over discharge, which I assume is the reason for the third lead. Would this protect the battery from getting fried by the external?

- The device normally charges with a 5v external plug, so I considered a 5v external power supply, but this would be bigger and less efficient. (would something like this work?) There is a doohicky on the market that does something like this, but it looks really crappy.

- The stock charger outputs 5v@1.5A, but the device can be also be charged with a PC USB, or regular dumb USB device chargers.

- I have ordered a replacement battery in case this doesn't work, so I can sacrifice the old one. Also I can test the setup outside of the PSP.

- I've got lipo charger, multimeter, soldering experience you would expect of someone who has been an electronics hobbyist for a decade.

I'm looking for advice, pointers, dos & don'ts, your own ideas, personal experience, etc.

Now lay into me.
sv650touring is offline Find More Posts by sv650touring
Reply With Quote
Sign up now
to remove ads between posts
Old Feb 25, 2011, 02:52 PM
Registered User
LeszekJ's Avatar
Poland
Joined Nov 2010
462 Posts
One cell - three wires.
Solve this puzzle at the beginning
LeszekJ is offline Find More Posts by LeszekJ
Reply With Quote
Old Feb 25, 2011, 03:18 PM
Only flies cheap
Florida
Joined Jan 2007
169 Posts
Quote:
Originally Posted by LeszekJ View Post
One cell - three wires.
Solve this puzzle at the beginning
I don't understand what you are saying.
sv650touring is offline Find More Posts by sv650touring
Reply With Quote
Old Feb 25, 2011, 05:17 PM
Registered User
ggcrandall1's Avatar
USA, GA, Marietta
Joined Aug 2005
5,796 Posts
He is saying figure out what the third wire is for before you start paralleling another battery.

Glen

After looking at the battery a bit more closely I would guess the "T" wire is a temperature sensor. If you are going to parallel with another battery and mount it externally the temperature sensing probably isn't too important. If you do go this route be sure you only use another lithium ion battery. Don't use a LiPoly. Their voltages are different. I would think the standard charger would charge both batteries. It will just take longer when charging two in parallel.
ggcrandall1 is offline Find More Posts by ggcrandall1
Last edited by ggcrandall1; Feb 25, 2011 at 05:27 PM. Reason: Added additional information.
Reply With Quote
Old Feb 25, 2011, 08:48 PM
Only flies cheap
Florida
Joined Jan 2007
169 Posts
Ahh yes, reading it now makes sense. And I think you're right about the T-lead (I've seen reference to over-temperature protection on this battery as well).

Thank you both for taking the time to respond.

But, from my reading, Li-Ion and Li-Poly batteries have the same nominal & maximum voltages, and you can use the same chargers on both types. Do you think they have significantly different voltage curves (at the very low rate of discharge this device would have)?

I was under the impression that when batteries are in parallel that if one falls below a voltage, the other will "try" to charge it up until they are equal. This is the sort of matter I was not sure of, thus my post.
sv650touring is offline Find More Posts by sv650touring
Reply With Quote
Old Feb 25, 2011, 09:45 PM
Registered User
ggcrandall1's Avatar
USA, GA, Marietta
Joined Aug 2005
5,796 Posts
LiPo cells have a full charge voltage of 4.2 volts. LiIon cells are fully charged at 4.1 volts. Not much of a difference but there is some. The chargers for these batteries generally have a separate setting for each of the battery types. I am not a battery guru and as such I would not parallel different types.

Batteries in parallel will always have the same voltage. A weaker battery still has the same voltage as a stronger one. Only the current provided by each battery in a parallel circuit will be different. If they were not at the same voltage level when they are initially connected they will equalize. Then as long as they remain connected the voltage level will remain the same at each battery. If you parallel batteries with different mah ratings, say a 1000mah and a 500mah the current supplied to the circuit will be proportional to each batteries capacity. So if the circuit requires 3000ma then the 1000mah battery will supply 2000ma and the 500mah battery will supply the remaining 1000ma.

Glen
ggcrandall1 is offline Find More Posts by ggcrandall1
Reply With Quote
Old Feb 26, 2011, 05:54 AM
Registered User
Melbourne, Australia
Joined May 2006
6,407 Posts
Q) Does the PSP work when connected to the charger?

If the answer is yes then a safe approach would be to use a DE-SW050 run from a 2S (or 3S if you like) lipo as the input and connect the 5.0V output to the PSP via the charger port. That would presumably let you use the PSP and when you are done, still have a charged internal battery.

This approach leaves manangement of the internal battery to the PSP which eliminates most of the potential safety/damage concerns.
kgfly is offline Find More Posts by kgfly
Reply With Quote
Old Feb 26, 2011, 07:17 AM
Registered User
Joined Apr 2010
21 Posts
Perhaps it might be better if you just connected a 18650 2-3Ah Lion cell in parallel to the stock battery. That should increase your psp battery lifespan by an additional two times. You could always parallel more 18650s if you need more juice. I would ignore the third wire if it's for temperature. You can then charge the whole thing including the extra battery with the stock charger or if you're sure about what you're doing, use your rc charger for a faster charge time.

Alternatively you could make yourself a battery pack, or if you already have one, connect it to a 5V BEC which then connects to a USB port. That should provide the juice you need for charging the psp on the go.
Schneizel is offline Find More Posts by Schneizel
Reply With Quote
Old Feb 26, 2011, 04:46 PM
Registered User
Vancouver, BC
Joined Jan 2011
189 Posts
Quote:
Originally Posted by ggcrandall1 View Post
LiPo cells have a full charge voltage of 4.2 volts. LiIon cells are fully charged at 4.1 volts.
Lithium ion cells generally available these days are said to be fully charged at 4.2V just as lithium polymer cells. For all intents and purposes they look and act the same, except they generally do not tolerate high rates of charge (or discharge, not an issue here) that lipo cells/packs can.

For the OP, is 5 volts actually present at the internal cell or is there additional circuitry inside the PSP bringing it to some regulated max voltage at 4.2 or less?
zapadoo is offline Find More Posts by zapadoo
Reply With Quote
Old Feb 28, 2011, 08:47 AM
Only flies cheap
Florida
Joined Jan 2007
169 Posts
Quote:
Originally Posted by zapadoo View Post
Lithium ion cells generally available these days are said to be fully charged at 4.2V just as lithium polymer cells. For all intents and purposes they look and act the same, except they generally do not tolerate high rates of charge (or discharge, not an issue here) that lipo cells/packs can.

For the OP, is 5 volts actually present at the internal cell or is there additional circuitry inside the PSP bringing it to some regulated max voltage at 4.2 or less?
According to the label on the battery, the maximum charge is 4.25v, so I reckon the PSP lowers the 5V that comes in from USB/charger.

Do you think Li-Po & Li-Ion similar enough that they could be run in parallel safely?

What if the Li-Ion was at a low state of charge and the Li-Po was fully charged? I would expect the claimed protection circuitry on the Li-Ion would prevent over charging. Are there any other concerns?
sv650touring is offline Find More Posts by sv650touring
Reply With Quote
Old Feb 28, 2011, 11:53 AM
Registered User
ggcrandall1's Avatar
USA, GA, Marietta
Joined Aug 2005
5,796 Posts
Quote:
Originally Posted by sv650touring View Post
According to the label on the battery, the maximum charge is 4.25v, so I reckon the PSP lowers the 5V that comes in from USB/charger.

Do you think Li-Po & Li-Ion similar enough that they could be run in parallel safely?

What if the Li-Ion was at a low state of charge and the Li-Po was fully charged? I would expect the claimed protection circuitry on the Li-Ion would prevent over charging. Are there any other concerns?
LiPoly batteries are easily abused and abused LiPoly batteries are prone to fail catastrophically (puff up and burn).

Since you don't know for certain if their are consequences in paralleling unlike battery types, I for one would not do that. Unless someone has documented proof that this can be done then my advice is don't.

Glen
ggcrandall1 is offline Find More Posts by ggcrandall1
Reply With Quote
Old Mar 01, 2011, 02:35 AM
eBike dude
neptronix's Avatar
Joined Mar 2011
20 Posts
No rocket science here.

Find the 'fully charged' voltage of the PSP go battery.
If it is 4.1v or 4.2v, lipo will work.

Then find the fully discharged voltage of the battery.
Is it above 3.0v?

Remember that lipo can charge from 3.0v to 4.2v. The meat of the charge is at 3.8v, so losing 0.1v is no big deal.

I would say only parallel the cell if the cell mAh is similar.

Another idea is to take some lipo cells and tape them on the back. Hook them up to where the stock battery was connected.. and create a protector out of plastic or ABS for the batteries so that you don't drop it right on the cell accidentally.. lol.

Yeah it would be ghetto but you could have 4x or more the battery capacity..

On the downside the stock charger would take forever to charge.. lol. it probably charges at a rate of 0.5amps or something.
neptronix is offline Find More Posts by neptronix
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Question How should I go about upgrading an Rc heli battery? Barretor Coaxial Helicopters 1 Feb 13, 2011 09:24 PM
Help! Using an aircraft-style radio for a submarine, programming advice requested MinuteHand Radios 9 Jan 30, 2011 11:55 PM
Discussion I Need To Make An Extended Battery Pack gapi Batteries and Chargers 9 Oct 31, 2010 03:34 PM
Mini-HowTo CX2 extended battery hanger using recycled training gear Heli Hacker Coaxial Helicopters 0 Sep 17, 2008 08:41 PM
Need advice for a college prototype project using Ducted Fans... XiiiXiii Electric Ducted Fan Jet Talk 14 Feb 16, 2004 09:30 PM