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I edited my earlier post to be clearer. Isolating the secondary batteries from the crank battery when the engine is not running is essential whatever system is used. The DC DC chargers make that simple by using an ignition wire to ensure that no current is drawn from the crank battery unless the alternator is running.
DC DC units are about optimising the charging of all batteries, and that is even more important when different types of battery are used - crank, auxiliary and trailer.
neil
I know Tim's Traxide unit has something like a 12v cutoff point for the isolator, so that his system isolates the crank battery at 12v from the aux battery/batteries.
My experience is that .. 'it depends'!Quote:
Originally Posted by Nmritchie
Personal experience with 18 months of having fitted my Redarc isolator:
The Redarc isolates at 12.7v.
I have fitted the manual override switch for my Recarc, but I stupidly used a momentary push button, and not a positive, or on/off switching type.
I did hotwire it a for a while so that I left the batteries connected over night for a few weeks.
In it's normal operation(not hotwired), with the isolator cutting in at 12.7v on the main battery, overnight the main battery would drop down to about 12.2 to 12.5 v, and the aux battery would always maintain about 12.5-12.8v. Always higher.
Obviously the aux battery is not in use, so this is just the typical every day usage pattern .. not when the aux is used to maintain a fridge or whatever!
When I had the wires hotwired to keep the solenoid active all the time for a few weeks, I found that both batteries held a minimum of 12.5v without fail, and many mornings noted that both batteries held 12.7v.
Only thing I didn't take note of (ie. remember) was the temperature of that morning .. ie. how cold it was for the batteries.
So my conclusion is that the traxide system of keeping both batteries connected for longer was better for the health of both batteries, and more so for the starter battery in every day type usage.
Both batteries connected for longer seem to help them maintain better health.
I don't have any starting issues with the Tdi and it does start with only a sec or two of cranking, but it did crank faster with the hotwire trick.
Of course you don't want it hotwired all the time, especially with a load on the aux battery. But I reckon an isolator with a variable cutoff point would be ideal.
I'd set mine to 12.2v, but I don't think I'd be worried about the 12.0v setting that Traxide uses either. A bit of piece of mind tho for really cold mornings for an old diesel to crank a bit faster .. just in case! .. it'd be nice to be able to vary the system to suit particular ambient conditions.
So, from my personal experience of someone that has a dual battery system, doesn't use it fully every day .. I wouldn't say it's essential to isolate the main battery from the aux batteries, so much as it's essential to keep all batteries at an optimal healthy level.
Having them connected for longer keeps them happier.
I currently have Century 720CCA batteries, so nothing special .. and when they eventually need replacing, I'll end up with Optimas of some description.
So, my question still stands ... why would you say that it's essential that the main battery is isolated from the aux battery/s when the engine is not running? I take that to mean that they should be isolated as soon as possible, or immediately, when the data points to the fact that the longer they maintain the connection, the better they both hold their charge.
ie. what benefit is there to the batteries with that claim?
All these fancy battery management devices are all well and good But do you Really need one?
While I am travelling I charge my auxiliary batteries via the trucks alternator which will charge them at a much greater rate than the usual 20A that a DC to DC charger pumps out and the cost to run a bit of wire and a couple of fuses is practically nothing compared to a battery management system and it also works on the K.I.S.S principle [thumbsupbig]
When I intend to stop in the one place for a while I will isolate my cranking battery from my auxiliaries simply by disconnecting an Anderson plug so that there is NO chance of it loosing its charge, I then run the fridges, lights, fans and whatever else I want to off the aux batteries which are charged via a couple of solar panels which pump out enough power to run the fridges AND keep up to 3x 110AH batteries topped up.
As I don't spend 100% of my time out bush my aux batteries are housed in ARK power boxes that are Not permanently fixed to the truck so I take them out and put them on float while I am not using them, Not much point in carrying about 100kg of batteries around if I am not using them.
The boxes are all fitted with dual Anderson plugs so that I can have them in series while travelling to keep them charged from the alternator and I can charge them all at the same time from the solar panels when camped up as well.
I have used the same system for a few years now without Any problems whatsoever.
So ask yourself again, Do I really NEED an expensive battery management device?
As the original poster I’m convinced that I don’t need a DCDC. There has been an awful lot of info posted, to which I’m grateful. Plus I’m grateful that I’ve run such thick cable as I’ve got plans to add extra batteries to the camper.
Something I may have missed though:
Is there a ‘I’m getting concerned that I’m not delivering enough volts’ number? Eg. say 13.5v is good, 13.0v = concerned, 12.0v=bad?
To where, or from where?Quote:
Originally Posted by John_D2
I'm assuming you mean along the 3B&S cable and to it's end, which is the house battery(s).
Do you have any way to keep an eye on voltages in the vehicle?
That is, volt meters for one or both(or more) of the batteries, independent of the cars electrical system?
On a battery with no load on it you should get a min 13.8v to it.
so if you're driving along and the aux battery(s) are just along for the ride, then I think the minimum voltage you'll get should be 13.8v or higher at that/those batteries.
If you have a load on the battery(eg. a continuously running fridge) then obviously that will cause the battery to show a lower voltage at it's terminals.
if your setup is fairly new it'd be a good idea to get a multimeter on each battery, car running, and with no loads on them as reference points.
If you run a fridge somewhere along the setup(eg. in the camper or in the back of the car or whatever) then also get a reference voltage measurement with that load on as well.
That first post showing 13.2v(at the starter battery) could be due to many loads on it. AC/heater running, with AC on, thermo fan also comes on, lights on? .. any other accessory on? .. etc.
Had a quick look at the install specs on that brake controller, and it seems that the electrical connection is via harness adapter into the trailer loom.
So it's voltage sense wire is going to be via the vehicles electrical system, so any accessories turned on in the vehicle will impact on the reading. Hence why some replies given were to measure the voltage of the battery at the terminals.
If you just buy a meter that plugs into the cigarette lighter it should show how much current from the alternator is running through the system when the engine is running.
My Defender shows about 13.9-14.0 all the time. I'd be concerned if it dropped below 13.
My batteries show a range of numbers depending on state of charge and load.
Remember that a battery reading of 12.0 means it is still about 50% charged.
How much Voltage i think you mean!Quote:
Originally Posted by DiscoMick
Where do you get these magical ampere meters that plug into the cigarette lighter?Quote:
Originally Posted by DiscoMick
I am pretty sure that Voltmeters were what was being referred to [thumbsupbig]Quote:
Originally Posted by Mick_Marsh
So, a voltmeter willQuote:
Originally Posted by trout1105
Where can I get one of those magical voltmeters then?Quote:
show how much current from the alternator is running through the system when the engine is running