Improving the CradlePoint PHS300’s battery life

March 30th, 2008

I love my PHS300. Being able to go out and having internet whenever I need it is really liberating. Of course there is one drawback; I’m talking about the battery life. I’ve turned the signal on the PHS down since it’s usually close by. I’ve found that typically I get 90 to 120mins connected time before my PHS300 battery gives up. Battery life is decent but it’s not long enough that I can leave it on whenever I’m out. I have to turn it on whenever I need it and remember to turn it off when I’m done.

When I’m out I usually bring a Toshiba Libretto (a small laptop with a 7″ display) plus the PHS300 and my modem. I carry it all in my man purse.

After reading a thread at EVDO forums, I was inspired to try making an external battery pack for my PHS. Rechargeable AA batteries have a voltage of 1.2 volts. 4 AA’s connected in series would yield a voltage of 4.8 volts which is close to the PHS AC adapter’s 5 volts.

I happen to have tons of AA rechargable batteries lying around from my SLR camera gear and various video game controllers. I have two types of batteries - Sanyo 2500mAh NiMH batteries which are the regular kind that discharge if you charge them and they sit on the shelf for a while. The other kind is Sanyo’s newer ENELOOP 2000mAh NiMH batteries. These have less capacity but only lose 15% of their charge per year (so they claim). Since I’m guessing they will only last a day or two I’m going to be using my 2500mAh cells.

I recharge the batteries with a Maha C801D.

Regular alkaline AA’s have a voltage of 1.5 volts and will fit but I’m not sure if the voltage is too high. I didn’t try them.

Before you read my instructions, here’s my disclaimer. If you break your PHS300 using my instructions it’s not my fault. If somehow you manage to set your PHS300 on fire it’s not my problem but please do send me a picture.

Here’s my instructions on how to make your own external battery pack. They’re actually very simple but in the interest of helping total electrical noobs (like myself) I’m being very very verbose.

Needed:

1. Soldering iron
2. Solder
3. Multimeter
4. Heatshrink wrap
5. 4 cell AA holder
6. Compatible plug
7. Wire stripper
8. AA NiMH battery
9. Hair dryer

Steps:

1. Stick AA batteries into the holder
2. Strip off some wire from the compatible plug. 1/4″ should do fine. Separate the wires for an inch or two.
3. Put some small heatshrink wrap on EACH wire from the AC adapter plug. You don’t need that much.
4. If you want a neater looking job, you can put a thicker piece of heatshrink wrap to cover the parts of wire that are separated.
5. Connect wires from the battery holder to the compatible plug. Connect the red wire from the battery pack to one of the wires on the compatible plug. Do the same with the black wire and the other wire on the compatible plug. Make sure the 2 sets of wires don’t touch.
6. Check polarity with the multimeter.
7. 
   1. Here’s how you do it: The PHS300’s plug polarity is like this -c+ the outside is negative and the inside is positive (see the picture above).
   2. Set your multimeter to measure DC voltage, you want it at a resolution that will handle around 6 volts.
   3. While the batteries are in the holder and the wires are connected, place the black tip from the multimeter on the outside of the plug and place the red tip from the multimeter on the INSIDE. Make sure the red and black wires from the battery pack are not touching each other.
   4. 
   5. If the voltage is +5 (around there, mine read 5.2 volts) you’re good to go. If the voltage is negative, the polarity is wrong. Swap the red wire from the battery pack with the black wire from the battery pack and test again to make sure it is now positive.
8. Solder the red wire from the battery pack with the wire from the AC adapter. Do the same with the battery pack’s black wire.
9. Wait for things to cool and then move the two thin pieces of heatshrink wrap over the exposed wire.
10. Use the blow dryer to shrink the wrap.
11. If you wanted a neater job, move the thicker piece of heatshrink wrap over the two smaller wires and shrink it with the blow dryer.
12. Check the polarity again. Make sure the voltage isn’t higher than 6 volts.

You’re done! Please note I don’t have any heatshrink wrap in my how-to pictures. I cut the wrap off of my setup to take pictures of it.

Using the new external battery pack I found my PHS battery life went from about 120mins to almost 7hrs. An increase of around 5 hrs. Please note I’m not constantly using the PHS300. A lot of the time it’s on but I’m not. 5 hr’s isn’t bad but it’s not quite enough for a long day. I ran out, got some more supplies and connected two 4 cell AA holders in parallel. Connecting them in parallel is the same as my instructions only you do this differently:

Connect the red wire from battery pack 1 to the red wire on battery pack 2 to the correct wire on the AC adapter plug. Do the same with the black wire from the battery packs, check polarity and solder. I connected the packs using some double sided tape and some parts I had lying around the house.

Now you get the same voltage but double the run time. Now I can get close to around 12 hrs of battery life. That’s good enough for me. If it’s not enough for you to make a battery holder with D cells (D cell NiMH batteries have capacities of around 10000mAh)

Since the battery pack is not that thick I can fit it, my laptop, modem and router in my man purse no problem. Sweet huh?

Howard Chui
03.30.2008

Entry Filed under: Latest Accessories, Phones