Bongo Fury

I've splashed out on an expensive stereo but disappointingly it's not happy running off the leisure battery. The voltage of the battery is all over the place and gets discharged and the stereo is trying to turn on. It may have something to do with the solar panels but I'm not sure. What I do know is I need to power the stereo from the usual starter battery.
I thought I'd be smart and just pull the cable to the fuse holder that runs the stereo from the LB but that also stops the cigar lighter running off the LB which I need to keep.
I can see this getting somewhat involved which I'm not overwhelmed with unless of course someone knows how I can easily run he stereo off the SB but keep the LB running the cigar lighters.
Thanks, Spud.

A couple of different problems I think;
First why is the leisure battery voltage varying so much? You need to find out why this is happening, it might be a poor connection to the battery, an old battery that is no longer holding its charge or an excessive load on the battery causing the problem.
I would suggest you need to check the state of the battery and its age, there should be a float indicator on the top of the battery that indicates the state of charge, and either a date embossed in the case or a label indicating the date if its more than 2-3 years old the battery may well be beyond its working life. If your relying on the solar panel then you might find that the battery is loosing charge when parked up in shade or close to a house such that the battery is still being discharged by devices connected whilst there is insufficient light to replace the charge each day.
If the charge state and dates are OK, then you really need a voltmeter to check the voltage at the battery terminals themselves Then follow the connections down thru the connectors, the fuses etc. its best to have a load on the circuit your testing to make sure that any bad connections show up.

As to the radio/audio device, they normally have two power connections, the first is the permanent unswitched supply (top left fuse on the internal fuse panel) used to backup the memories, the second is the switched supply (top right connection on fuse panel) for the main current draw when the device is operating. When connected to a LB rather than the SB via the Ignition switch you have to rely on the On/Off switch on the device - not all modern devices have there own switch!!! You either need to supply your own switch, or on some LB wiring kits this is built in with a separate switch for this purpose. Its best NOT to run the device from both / split batteries as there can be feedback paths thru the radio to the other battery causing even more problems!

Hi, the original stereo (cheap Chinese double din £40) mustn't have drawn much power as I never had any issues with it for years other than the screen went bad.

I then bought a more expensive Chinese one with phone mirroring etc and that's initially when the issues started. It would turn itself on, flatten the LB within a day and be running red hot. I put my battery charger on it but even that couldn't keep up at 5A supply, not bad for a stereo that wasn't switched on. I read that a lot of the issues I was having were actually quite common in Android stereos but quite rare in brand stereos so I forked out for a Kenwood. Unfortunately the other stereo killed off my LB which was quite old anyway so that was replaced with new. I also replaced the SB for good measure. I also noted that after driving the split relay would be constantly flicking as if it didn't know what to do. Probably because of the varying voltages.

Plug the new stereo in and behold you can see the voltage start to drop surprisingly quickly especially as the panels are still supplying. I didn't realise at first but after I'd noticed and put a meter on it the voltage was all over the place, 8, 12,9 10v etc etc.

I opened up my phone to see what the panels were doing and it was reading the same varying voltages on that as well. I thought I'd killed another LB but unplugging the stereo the voltage went back to a solid 12v.

I'm assuming the new stereos are not happy having a permanent supply for the switched and constant supply which is what the LB looks to be wired to do. Although that doesn't explain if it was connected normally through a SB how they would react if the engine was on and the radio just switched off as it would be getting both supplies then.

I was originally thinking of just piggy backing a fuse that would give a switched supply but that would mean using the 2 different batteries which you warn against and have ruined my next experiment.

Putting a switch in the "switched" wire to the stereo might be the answer but it doesn't really explain why when I plug my old stereo back in it doesn't have the same problem.

Without using a voltmeter to check the voltage and currents being drawn at various points between the battery and the device it can be difficult to diagnose the problem. Most situations where the voltage is varying a lot over a short time is usually a bad connection, hence the need to start at the battery terminals check the voltage, then on the clamps, then down to the fuses etc.

I've managed to sort it with a switch from the leisure battery. There wasn't anywhere else, including under the bonnet, where I could successfully piggy back off so a switch was the way to go. The stereo is now happy and so are the batteries. I'm still getting a switching of the split charge relay when I start and stop the engine more than I remember it doing, but that started before my stereo debacle. Thanks for the reply Geoff.

A lot of the SCR are voltage sensitive, they look for one or the other battery to be above 13 volts approximately (i.e. being charged) then they operate to connect both batteries in parallel to the charging source, however its quite common for a battery to remain above 13 volts for several minutes after being charging has stopped thus the relay operates at which point the extra current being drawn causes the voltage to fall and the relay drops out, now with the current reduced the voltage goes back up again and the relay operates again! This can continue for several minutes until the battery falls back to the normal 12.6 to 12.8 volts which is the normal resting voltage at which point the SCR stops clicking and the batteries are isolated. You may also find that if you have a Solar Panel charging the LB then the same happens.