Philips PRP 74 battery development - UK Vintage Radio Repair and Restoration Discussion Forum

Llewof1701 · 2nd Dec 2018, 2:40 pm

Hi all, first post here so please bear with if its in the wrong section.

I'm an instructor at a local Air Cadet squadron and am trying to return about 6 radios to working condition. All the radios are PRP 74, some made by Philips and some made by Simico.

The main problem with them all is that the old nickel cadmium batteries are all completely dead. My aim is to redesign the battery pack to use 18650 Lithium Ion cells and 3D print an enclosure to replace the OEM battery pack.

Having hopefully identified the correct pinout for the battery connection and tested it with 2 18650's in series and a thermistor (including pull up resistor), I've had little luck. The original battery packs ran at 7.2V and supposedly 2000mAh. The 18650 set up I'm planning on using should match this.

I'm basically after any advice if people have tried this before or can help to diagnose some of the issues I'm coming across. I'm happy to publish the CAD files for the battery enclosure when the projects is finished if anyone would find them useful.

Thanks, Kieran

Stockden · 2nd Dec 2018, 8:23 pm

Hi Kieran,

I was asked to do something similar some years ago by a local Sea Cadet unit, who had inherited the radios from the ATC. The problem was exactly the same, dead and corroded batteries. To be honest I didn't get very far, largely because I didn't have any way of manufacturing new battery cases.

I think I still have a copy of an AESP for one of the PRP7x variants somewhere. If it'd help I'll dig it out and see if it says anything useful.

Hugh

Maarten · 2nd Dec 2018, 8:39 pm

Battery cases could be made in small series by 3D printing.

In any case, a 2S configuration of normal lithium cells will have a usable voltage range of 6.4 to 8.4 volt for maximum use of capacity or 7.2 to 8.0 volt for maximum life (voltage corresponds to state of charge).

If the PRP74 can deal with this input voltage range, the next problem is that you will need to make a custom charger. No way they can be charged using the NiCd charger, unless you accept short cell life and a non-zero chance of fire and explosion.

Nickthedentist · 2nd Dec 2018, 8:50 pm

NiMH?

Sparky67 · 3rd Dec 2018, 12:14 am

Hi Kieran,

I understand your interest in the project to replace the batteries, however, if they haven't been already, can I suggest the PRP74s are tested on a 7.2V bench PSU to make sure they still have their data fill intact. If those particular sets are from a batch supplied through the ATC some years ago and have dropped their fill, or show signs of needing refreshing (odd things on the LCD), they cannot be reprogrammed. Might save you some time and trouble...

From my experience of old PRPs they do have a finite life, particularly if they haven't been used for a while or have been stored in cold/damp conditions. If they are showing signs of expiring, I would suggest long-term the cadet unit would probably be better off buying Baofeng 888s or UV-6Rs or similar for the cadets to use when training. Which is what I have just done!

Cheers,

Martin
G4NCE

2nd Dec 2018, 2:40 pm	#1
Llewof1701 Retired Dormant Member Join Date: Dec 2018 Location: York, North Yorkshire, UK. Posts: 1	Philips PRP 74 battery development Hi all, first post here so please bear with if its in the wrong section. I'm an instructor at a local Air Cadet squadron and am trying to return about 6 radios to working condition. All the radios are PRP 74, some made by Philips and some made by Simico. The main problem with them all is that the old nickel cadmium batteries are all completely dead. My aim is to redesign the battery pack to use 18650 Lithium Ion cells and 3D print an enclosure to replace the OEM battery pack. Having hopefully identified the correct pinout for the battery connection and tested it with 2 18650's in series and a thermistor (including pull up resistor), I've had little luck. The original battery packs ran at 7.2V and supposedly 2000mAh. The 18650 set up I'm planning on using should match this. I'm basically after any advice if people have tried this before or can help to diagnose some of the issues I'm coming across. I'm happy to publish the CAD files for the battery enclosure when the projects is finished if anyone would find them useful. Thanks, Kieran

2nd Dec 2018, 8:23 pm	#2
Stockden Heptode Join Date: Mar 2008 Location: Forest of Dean, Gloucestershire, UK. Posts: 648	Re: Philips PRP 74 battery development Hi Kieran, I was asked to do something similar some years ago by a local Sea Cadet unit, who had inherited the radios from the ATC. The problem was exactly the same, dead and corroded batteries. To be honest I didn't get very far, largely because I didn't have any way of manufacturing new battery cases. I think I still have a copy of an AESP for one of the PRP7x variants somewhere. If it'd help I'll dig it out and see if it says anything useful. Hugh

2nd Dec 2018, 8:39 pm	#3
Maarten Dekatron Join Date: Dec 2007 Location: Haarlem, Netherlands Posts: 4,199	Re: Philips PRP 74 battery development Battery cases could be made in small series by 3D printing. In any case, a 2S configuration of normal lithium cells will have a usable voltage range of 6.4 to 8.4 volt for maximum use of capacity or 7.2 to 8.0 volt for maximum life (voltage corresponds to state of charge). If the PRP74 can deal with this input voltage range, the next problem is that you will need to make a custom charger. No way they can be charged using the NiCd charger, unless you accept short cell life and a non-zero chance of fire and explosion.

2nd Dec 2018, 8:50 pm	#4
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,837	Re: Philips PRP 74 battery development NiMH?

3rd Dec 2018, 12:14 am	#5
Sparky67 Heptode Join Date: Feb 2008 Location: Great Barr, Sandwell, West Midlands, UK. Posts: 589	Re: Philips PRP 74 battery development Hi Kieran, I understand your interest in the project to replace the batteries, however, if they haven't been already, can I suggest the PRP74s are tested on a 7.2V bench PSU to make sure they still have their data fill intact. If those particular sets are from a batch supplied through the ATC some years ago and have dropped their fill, or show signs of needing refreshing (odd things on the LCD), they cannot be reprogrammed. Might save you some time and trouble... From my experience of old PRPs they do have a finite life, particularly if they haven't been used for a while or have been stored in cold/damp conditions. If they are showing signs of expiring, I would suggest long-term the cadet unit would probably be better off buying Baofeng 888s or UV-6Rs or similar for the cadets to use when training. Which is what I have just done! Cheers, Martin G4NCE Last edited by Sparky67; 3rd Dec 2018 at 12:42 am.