Powering the memory +12v - radio

HarryM1BYT · 7th October 2016, 18:01

I have the main +12v and the memory +12v wired together from the +12v in the van, trouble is when I isolate the 12v via the master switch when we go out, it looses all the radio stations in its memory. I don't want to run a separate always on 12v, so I'm trying to find a work around.

I tried a PP3 battery and it doesn't have enough voltage to allow the radio to boot itself up. My next idea is a Farad capacitor, charged when the 12v is on by a diode. I used to have some decades ago in my workshop, I just need to look in the right place

rrobson · 7th October 2016, 21:40

What about a smallish 12v lead acid rechargeable? Charge it up at home or while connected to mains and wire the memory to the battery. Without a constant live 12v you'll need to store power somehow. Depends how long you need it to remember stations before it's de-isolated.

clf · 7th October 2016, 22:28

Quote:

Originally Posted by HarryM1BYT

I have the main +12v and the memory +12v wired together from the +12v in the van, trouble is when I isolate the 12v via the master switch when we go out, it looses all the radio stations in its memory. I don't want to run a separate always on 12v, so I'm trying to find a work around.

I tried a PP3 battery and it doesn't have enough voltage to allow the radio to boot itself up. My next idea is a Farad capacitor, charged when the 12v is on by a diode. I used to have some decades ago in my workshop, I just need to look in the right place

How long will you be out? The amount of current draw whilst you are out (assuming it is just for the day/evening) would be minimal, so a cable taken directly to the battery along with an inline fuse close to the battery would work. Simple and effective.

Even rigging a switch to it, so when the van is parked up for long periods, it can be switched off. Again making an assumption. That the battery is not removed completely to charge etc.

HarryM1BYT · 8th October 2016, 08:18

Quote:

Originally Posted by clf

How long will you be out? The amount of current draw whilst you are out (assuming it is just for the day/evening) would be minimal, so a cable taken directly to the battery along with an inline fuse close to the battery would work. Simple and effective.

Even rigging a switch to it, so when the van is parked up for long periods, it can be switched off. Again making an assumption. That the battery is not removed completely to charge etc.

It would be quite difficult to get a feed to it from the battery, it is not an easy run - besides, I am trying to avoid having anything being left on. I am not at all concerned about the tiny current it would draw, I suspect that will be just uA. It is on hook up when on site and when at home too.

Hence my reasons to look at other ways to give it a low current, 12v source.

clf · 8th October 2016, 13:37

Quote:

Originally Posted by HarryM1BYT

It would be quite difficult to get a feed to it from the battery, it is not an easy run - besides, I am trying to avoid having anything being left on. I am not at all concerned about the tiny current it would draw, I suspect that will be just uA. It is on hook up when on site and when at home too.

Hence my reasons to look at other ways to give it a low current, 12v source.

I don't know how long it would hold charge for, or how safe it would be. You tried a 9 volt battery, which I don't think would be enough, so what about 8 flat lithium batteries, the type used in computers for clock back up. Stack them, wrapped together, and tucked behind the stereo unit? A pack of pound land batteries shoved be enough to experiment with.

electrocop · 8th October 2016, 15:32

I would not recommend using 8 flat lithium batteries (I assume type CR2032?) - those are 3V each and would therefore give you 24V.
Also, it is not wise to leave them connected when the power supply is reapplied.

I would second rrobson's suggestion about using a small lead-acid battery. It would keep the memory for quite a while and wouldn't mind when the main power is reapplied - it would just re-charge. I would add a blocking diode though, to ensure that the back-up supply cannot be fed inadvertently to other appliances in the caravan.

My other suggestion would be to change the radio for one of the older 1990's snatchable types - they either had a built in battery to keep the memory or had a non-volatile memory chip.
I used a high-end Pioneer removable radio/cassette in my caravan and that never lost it's memory (my reason for choosing it)

HarryM1BYT · 8th October 2016, 15:41

Quote:

Originally Posted by clf

I don't know how long it would hold charge for, or how safe it would be. You tried a 9 volt battery, which I don't think would be enough, so what about 8 flat lithium batteries, the type used in computers for clock back up. Stack them, wrapped together, and tucked behind the stereo unit? A pack of pound land batteries shoved be enough to experiment , sowith.

I've just experimented a bit more and...

When the set is turned on and in use, it draws around 0.7amps via the memory +12v. When off just a few uA as I expected. So its not really do-able without some clever circuitry, so best that I abandon the idea.

It was just to avoid the need to have to retune it every time I switched the power back on.

NigelOBB · 9th October 2016, 09:14

Mines just feeds straight from my Backup battery, which I keep top up using a solar panel. It's never let me down for a few years, touch wood.

Sent from my iPhone using Tapatalk

7th October 2016, 18:01	#1
HarryM1BYT This is my second home 75 Contemporary SE Mk II 2004 Man. Sal. CDTi 135ps, FBH on red diesel, WinCE6 DD Join Date: May 2010 Location: Leeds Posts: 17,273 Thanks: 2,160 Thanked 2,061 Times in 1,586 Posts	Powering the memory +12v - radio I have the main +12v and the memory +12v wired together from the +12v in the van, trouble is when I isolate the 12v via the master switch when we go out, it looses all the radio stations in its memory. I don't want to run a separate always on 12v, so I'm trying to find a work around. I tried a PP3 battery and it doesn't have enough voltage to allow the radio to boot itself up. My next idea is a Farad capacitor, charged when the 12v is on by a diode. I used to have some decades ago in my workshop, I just need to look in the right place __________________ Harry How To's and items I offer for free, or just to cover the cost of my expenses... http://www.the75andztclub.co.uk/foru...40#post1764540 Fix a poor handbrake; DIY ABS diagnostic unit; Loan of the spanner needed to change the CDT belts; free OBD diagnostics +MAF; Correct Bosch MAF cheap; DVB-T install in an ex-hi-line system; DD install with a HK amp; FBH servicing. I've taken a vow of poverty. To annoy me, send money. Last edited by HarryM1BYT; 7th October 2016 at 18:08..

7th October 2016, 21:40	#2
rrobson I really should get out more....... 75 tourer cdti, MG ZS 180, nissan terrano & 1.8t rover 25 Join Date: Feb 2010 Location: Pontefract Posts: 2,643 Thanks: 17 Thanked 295 Times in 218 Posts	What about a smallish 12v lead acid rechargeable? Charge it up at home or while connected to mains and wire the memory to the battery. Without a constant live 12v you'll need to store power somehow. Depends how long you need it to remember stations before it's de-isolated. __________________ How to view a car - everything you need to help you inspect a used car VIS motor tester avalible to local members Injector removal tool and auto gearbox pressure tester now available

9th October 2016, 09:14	#8
NigelOBB This is my second home 04 Rover 75 Contemporary SE - 53 Rover 75 Connoisseur -94 Mercedes W140 - 72 VW Beetle 1300 Join Date: Sep 2012 Location: Sunderland Posts: 4,767 Thanks: 1,379 Thanked 493 Times in 429 Posts	Mines just feeds straight from my Backup battery, which I keep top up using a solar panel. It's never let me down for a few years, touch wood. Sent from my iPhone using Tapatalk __________________ [SIGPIC][/SIGPIC] Keep smiling - it makes people wonder what you've been up to.

8th October 2016, 15:32	#6
electrocop Avid contributor Rover 75 Tourer Join Date: Oct 2015 Location: Derbyshire Posts: 104 Thanks: 11 Thanked 24 Times in 21 Posts	I would not recommend using 8 flat lithium batteries (I assume type CR2032?) - those are 3V each and would therefore give you 24V. Also, it is not wise to leave them connected when the power supply is reapplied. I would second rrobson's suggestion about using a small lead-acid battery. It would keep the memory for quite a while and wouldn't mind when the main power is reapplied - it would just re-charge. I would add a blocking diode though, to ensure that the back-up supply cannot be fed inadvertently to other appliances in the caravan. My other suggestion would be to change the radio for one of the older 1990's snatchable types - they either had a built in battery to keep the memory or had a non-volatile memory chip. I used a high-end Pioneer removable radio/cassette in my caravan and that never lost it's memory (my reason for choosing it)