Radio battery backup

[Mike_S]

I have replaced the AM/FM Pioneer radio in my Coachman with a similar Pioneer unit that also gives DAB reception. I’ve included a VisionPlus diplexer to feed the separate FM/AM and DAB antenna sockets in the radio unit. I’m delighted with the performance of the new radio.
The only downside is that when the 12v supply to the radio is cut off as it is when the caravan battery is disconnected either by the main switch on the caravan control panel or when the caravan’s habitation relay activates whilst towing, the radio “forgets” everything – not only the radio stations tuned in (which are relatively easy to retune) but also other settings for the display, type of antenna, etc, which are much more fiddly to reset.
Ignoring the speaker connections at the back of the radio, the 12v connections are as follows
Black – 12v neg
Red - 12v pos – the “main” power supply to the radio to enable it to work (in a car this would become live when the ignition is switched on)
Yellow - 12v pos – a permanent supply to the radio to keep the radio memory active

Any suggestions as to how I could maintain 12v through the yellow wire to save the contents of the radio’s memory?
I imagine that the current carried by the yellow wire is in the order of milli-amps, although I haven’t measured it yet.
Perhaps a 9v PP3 battery may be sufficient to maintain the memory but would need some sort of blocking diode to prevent the 12v supply attempting to recharge it.
Has anyone out there got a solution?

Mike

 

[Thingy]

In lieu of a satisfactory answer from the forum, have you thought of asking a car radio shop?

 

[ericmark]

I have considered a 9 volt battery, diodes etc. However I in the end simply swapped the radio supply at the fuse box so it is supplied all the time, even with master off.

 

[ProfJohnL]

Before being able to offer an effective solution I would need to do a few tests to see if there is any internal connection between the red and yellow wires.

If there is no connection then I would consider setting up a modest diode forward baised between red and yellow, and fitting a 2Ah rechargable 12V SLA battery from Yellow(+) and 0Volts.

The small battery will maintain the memory, but it will be charged through the diode when ever the caravans 12V system is active. The diode will prevent the small battery backfeeding the 12V circuit when the caravsn 12V system is off.

By using a rechargable, it negates the need to change the battery.

I'm not sure if a 9V cell would have enough Voltage to power the internal circuits, and the the current drain may be too high for the battery to sustatin it during storage.

 

[JTQ]

My Hymer came with a Pioneer and stupidly wired in just the same way, it lost its memories when the habitation relay chopped the supply. Also wired as it was it was very a significant power drain when not in use.
I ran a single core positive, "maintained" supply back to the battery, and introduced a neat toggle switch into the original power feed to replicate the missing "ingition" switch that these car intended units need when used in caravans. Stupid original design.
The maintained supply I measure was but a few milli amps, but I have no record as this was 12 years ago. Clearly that feed was suitably fused.
Edit: Note in my case I only needed the positive maintained supply, not both cores, the negative in my case was not chopped by the habitation relay; would be worth checking if that is typical, as then it halves the task.
I discovered the large drain when "off", by suffering a drained battery on the first off grid outing!

 

[Woodentop]

That is why - for instance Bailey - only fit JVC or certain models of Pioneer and possibly Sony, as whilst these models do forget the screen settings they don't forget the station memories.
To the OP, one thing I found is that on one radio it appeared to have forgotten the stations, but in fact at power up if the station change button was used the stations were actually there. It was a four-way rocker button where left and right went up and down the frequencies, and up and down went up and down the stations memories. If first press was the up button the stations would appear.

 

[ProfJohnL]

... Stupid original design....

I'm sorry but I have to disagree!

The radios are not designed for caravans as their name suggests they are car radios. With the advent of fully digital tuners some form of electronic memory was needed to record and keep user preferences. Because in a car there is a large battery they could use a separate power feed to keep the memory powered when the auxiliary power was cut when the ignition circuit was turned off.

However I do agree that these days there are different solutions that would not require a continuous power feed, but I suspect that with many car radio manufacturers, the addage of 'if its not broken don't fix it's may come into play which could be why they haven't redesigned the memory retention system.

Perhaps with the adoption of ev's where electrical power is a key and critical commodity, the motor manufacturers will be asking ICE manufacturers for more efficient radio packages.

 

[Woodentop]

Interesting that when Philips made car radios - and I mean from the 70's right up until and including DAB units - they never had a problem of forgetfulness. Why? Because they stored the settings and memories in non-volatile memory. I was once told they used a type of memory chip that had the operating system permanently in it like a PROM but the same chip encapsulation also had a small quantity of EAPROM. It may have started because of the way that German radio broadcasts RDS which can result in the radio taking up to 40 minutes to learn the Alternative Frequency tables. If it lost that info at switch off it would effectively negate the benefits of RDS and especially AF in an instant.

 

[JTQ]

... Stupid original design....

I'm sorry but I have to disagree!

The radios are not designed for caravans as their name suggests they are car radios. With the advent of fully digital tuners some form of electronic memory was needed to record and keep user preferences. Because in a car there is a large battery they could use a separate power feed to keep the memory powered when the auxiliary power was cut when the ignition circuit was turned off.

However I do agree that these days there are different solutions that would not require a continuous power feed, but I suspect that with many car radio manufacturers, the addage of 'if its not broken don't fix it's may come into play which could be why they haven't redesigned the memory retention system.

Perhaps with the adoption of ev's where electrical power is a key and critical commodity, the motor manufacturers will be asking ICE manufacturers for more efficient radio packages.

The "stupidity" as I said was the wiring in the caravan, without a sustained supply and the replication of the ignition switches function. Features these automotive "radios" were designed to operate correctly with, and so simple to provide, just needing a modicum of design understanding.
If you take a product from a different market, the least I would expect of the van's electrical system designer is to read the installation manual and provide the salient features it requires.

 

[Icaru5]

... Stupid original design....

I'm sorry but I have to disagree!

The radios are not designed for caravans as their name suggests they are car radios. With the advent of fully digital tuners some form of electronic memory was needed to record and keep user preferences. Because in a car there is a large battery they could use a separate power feed to keep the memory powered when the auxiliary power was cut when the ignition circuit was turned off.

However I do agree that these days there are different solutions that would not require a continuous power feed, but I suspect that with many car radio manufacturers, the addage of 'if its not broken don't fix it's may come into play which could be why they haven't redesigned the memory retention system.

Perhaps with the adoption of ev's where electrical power is a key and critical commodity, the motor manufacturers will be asking ICE manufacturers for more efficient radio packages.

The "stupidity" as I said was the wiring in the caravan, without a sustained supply and the replication of the ignition switches function. Features these automotive "radios" were designed to operate correctly with, and so simple to provide, just needing a modicum of design understanding.
If you take a product from a different market, the least I would expect of the van's electrical system designer is to read the installation manual and provide the salient features it requires.

The problem is JTQ, if the radio was wired with the permanent live connection for memory retention, then people would be complaining that that permanent 12V feed to the radio is draining and killing their battery. In which case, they’re damned if they do, damned if they don’t. Of course, as the Prof and Woodentop correctly point out, there are other alternatives in the form of NVRAM with negligible cost, however, as these units are designed primarily for use in a car where the problem doesn’t exist, the low end Chinese manufacturers producing such units as the JVC branded sets that were for years supplied by Swift are very unlikely to implement design changes to satisfy a minuscule percentage of the market.

When you consider that such sets have a single unit retail selling price of around £40, and are years old in terms of design, you can imagine the sort of money the caravan manufacturers are paying for them in bulk quantities !

It may well be that some of the more premium units on the market today do indeed use NVRAM to store settings and of course you always have the choice to upgrade, but I have absolutely no idea, and as I’d hardly call having to “Autotune” the set to my preferred radio station after pitching up a real problem, I have no interest in investigating.

You could always supply a permanent 12V to the yellow, connected through a neatly mounted bulkhead switch next to the radio that so that you can switch off the feed when the van is in storage.

 

[Mike_S]

Good evening Prof.
Thanks for your reply. I’ve done a few more tests.
There is no internal connection between the red and yellow wires.
The red and yellow wires are fed from the same fuse in the fuse box.
The current when the radio is on standby is around 200mA, when playing around 850mA.
Correct me if I’m wrong but if the small backup battery is connected to the 12v yellow and 0v then a diode should be wired into the supply side of the yellow so the backup battery can be recharged by the caravan but cannot be discharged “back” through the caravan when the main battery supply is not connected.

Regards
Mike

 

[Woodentop]

Good evening Prof.
Thanks for your reply. I’ve done a few more tests.
There is no internal connection between the red and yellow wires.
The red and yellow wires are fed from the same fuse in the fuse box.
The current when the radio is on standby is around 200mA, when playing around 850mA.
Correct me if I’m wrong but if the small backup battery is connected to the 12v yellow and 0v then a diode should be wired into the supply side of the yellow so the backup battery can be recharged by the caravan but cannot be discharged “back” through the caravan when the main battery supply is not connected.

Regards
Mike

I have to say, having spent nearly 40 years in radio comms, that I am surprised that the standby current drawn is as high as 200mA. I would suggest the OP separates the live and memory wires and measures the memory current - which I would expect to be well less than 1mA. If that is the case then a 12V 1.2Ah lead acid battery with a small solar panel charging it would be a very good option.
Having said that, time was that cars had Smiths analogue clocks in them and such a clock could flatten the car battery in a week!

 

[ProfJohnL]

Good evening Prof.
Thanks for your reply. I’ve done a few more tests.
There is no internal connection between the red and yellow wires.
The red and yellow wires are fed from the same fuse in the fuse box.
The current when the radio is on standby is around 200mA, when playing around 850mA.
Correct me if I’m wrong but if the small backup battery is connected to the 12v yellow and 0v then a diode should be wired into the supply side of the yellow so the backup battery can be recharged by the caravan but cannot be discharged “back” through the caravan when the main battery supply is not connected.

Regards
Mike

Hello Mike,

That is what I effectively suggested.

I do agree with Woodentop, a 200mA current in stand by does seem very excesive even for a car, I'd susspect thet either you have meassured incorrectly, or there is something wrong with the radio or its installation.

The radio will have three power states, On when its playing, standby when its not playing but its still connected to the incomming supply, and Off when the red wire is not connected to 12V.

What you need to do is to check the current through the yellow wire when the red is actually disconnected, and I susspect the current will be much less than 200mA

 

[Mike_S]

Good evening Prof and Woodentop

Disconnecting the red live has indeed made a huge difference to the reading on the yellow wire. It's now a much more realistic 4.5 mA.
All I need do now is source an appropriate battery and diode then it's out with the soldering iron!

Many thanks
Mike

 

[ericmark]

Having to retune when you get to site is not a problem, However having the ratio running in demo mode until you can get into caravan to turn it off is a problem. And with the radio I fitted if it looses and regains power it auto switches on in demo mode, so the radio is playing all the time you are towing and setting up caravan, plug in 13 pin socket or unplug 13 pin socket and radio auto switches on in demo mode.

I simply swapped the feed at fuse box to always on. This means switch it off and it stays off.

However it seems the large battery isolator which I thought would turn off battery, after all that is what a battery isolator is for, in fact only turns off the motor mover, and the master switch when off still leaves battery charger connected so always a small drain, only way to stop small drain is take battery terminal off.

The drain from built in aerial booster is likely more than radio, as yet unmeasured.

Looked at fitting a VRLA 7Ah which I had, but not enough room with radio, and at fuse box it would also power aerial booster, so two ideas.

One is a 9 volt battery to maintain radio memory, the other is a capacitor, the latter would not last long, however likely long enough to stop demo mode when plugging and unplugging 13 pin plug. However a capacitor will not over or under charge.

But since no alarm or any other reason why the caravan needs a battery while stored, the simple method is to leave as it is with radio always powered and remove battery when in storage and put a smart charger on the battery at home, so always start with fully charged battery.

I suspect the 200 mA is not what radio is using, but what radio plus aerial amplifier is using. I would have expected more like 5 mA in standby. A PP3 typically around 200 mAh so even at 5 mA only 40 hours, and at 200 mA just one hour, so hardly worth it.

I did not measure what my radio uses, however I did measure what the whole caravan uses, which was 2 watt, so can't see how radio can be using 2.4 watt.

 

[Craigyoung]

I always make sure my radio switched to the power of and unclipped and as for my radio booster or aerial booster that is in the cupboard I undo the red lead so the LED is not lit and powered whilst everything else is shut down .

 

[Hutch]

Similar problem with our radio, disconnect power and on reconnection the demo mode comes on, not really a problem, hit the demo off button, I disconnect the battery through an isolator as the fridge and awning light are always powered even with the caravan master switch off, otherwise the battery will be discharged to 12.4 volts in 4 weeks.

 

[ProfJohnL]

Good evening Prof and Woodentop

Disconnecting the red live has indeed made a huge difference to the reading on the yellow wire. It's now a much more realistic 4.5 mA.
All I need do now is source an appropriate battery and diode then it's out with the soldering iron!

Many thanks
Mike

Thank you for the response, it's nice to know when advice or information given has helped or at least confirmed the diagnosis.

Whilst I do know how annoying having to retune a radio can be, (I have a Pure DAB tuner at home that looses it's memory, it's know fault for this particular model), but in a touring caravan, where setting up in different areas will mean several of the FM stations will be on different frequencies, then you are likely to have to retune any way. I actually derived some pleasure from retuning, and discovering what stations were available at a new site.

With a drain on the yellow wire of 4.5mA, and the internal losses that a battery naturally has, realistically I would only expect a battery to last about a week for every Ah of battery capacity. If you don't use the caravan very often then even with a battery backup as I've suggested previously, you might come to find it has lost its memory after few weeks of storage.

You should also remember that having another battery is going to eat up some payload capacity.

Just another thought if the extra battery does get seriously discharged, when the caravans 12v system is turned on again the extra battery could try to draw a substantial current which might take out the diode. I would suggest fitting a 10W 10 Ohm resistor in series with the diode to limit the current feed to the new battery. IN4001 should be sufficient.

 

[Mike_S]

Good morning Prof (and others)

Re-reading the advice and suggestions given by yourself and others I decided to take a simpler solution to the problem.
The idea of a second rechargeable battery, with or without solar backup etc, was rejected. Instead, I have taken a “permanent 12v live” from the caravan battery to the yellow wire at the radio. In reality I’ve added a connector to the input side of the motor mover isolating switch then wired through a 3Amp in-line fuse up to a bullet connector to join with the yellow wire at the back of the radio. Typical of these jobs, the electrical work itself took about 10 minutes: hiding the wire through lockers, plastic trim etc took much longer!
I’m pleased to report that the setup works and I now even have the radio displaying the date and time when switched to standby. I’m not worried about the caravan battery being discharged as, keeping the ‘van at home, it is frequently hooked up!

My thanks again

Mike

 

[Gozza]

Just a thought, but if you're going to retune at every new site you get to, what would be the consequence of just disconnecting yellow altogether? If it's a coded radio then you'd have to re-enter the code every time you switched on whatever is powering the red line (12 v master switch presumably) but otherwise is it likely to cause any issues?

Certainly with the antique radio in my van it doesn't, because my leisure battery is also an antique and gets removed a couple of times a year to take home for a full charge / maintenance cycle, and the radio is fine afterwards. Don't know what the result would be with a newer radio however.

 

[Mike_S]

Hi Gozza

The radio doesn't have a security code that needs keying in so that's one less bit of hassle! I have tried disconnecting the yellow lead completely - the radio doesn't work at all.

Mike

 

[Gozza]

Ah well...it would've been a good idea if it wasn't for the fact it wasn't!