Thread: Yet another DC-DC charger discussion

Ranga, I have an sc80 in our amarok, it charges a battery about 4m away, then charges another 2 batteries another 4m away. It works great. This guy is talking BS. I'm running 13.5mm2 cable, has less than .1v drop at its final destination.

The bloke "a flowing body of water" is proof that you don't have to be technically capable or correct to have your scribblings published...

I'm sure Drivesafe will wander in here soon...

Take a Deep Breath Tim!

God knows this has been done to death, but then I always settle in with a bowl of popcorn and a beer when these threads come up.

The charging of the aux batteries with varying length of cable, is simply a function of time. Of course they will charge, it might just take longer, if, there is some significant loss on the cable. As for DC-DC, if it is supposed to charge the batteries quicker than the alternator, from a low soc, how are you supposed to get the current there if, all other things being equal, there is major loss on this long cable. Its bollocks. Helpful hint though, if you want Tim to stay sane, I wouldn't mention the name Collyn Rivers.

Originally Posted by Vern

This guy is talking BS.

Vern, did you get that in one.

Ranga ( and everyone else ) for a starter, who ever was giving you the “ADVICE” ( read B/S ), once a motor is running and the alternator is providing power to the vehicle ( this can be a few minutes after the motor is started ) the alternator CAN NOT SENSE THE STATE OF THE CRANKING BATTERY.

The only voltage that is being “SENSED” is the alternator’s own voltage and this will usually be much high than ANY battery’s voltage.

Next, in this day and age, very few caravans will have a blocking diode fitted, these went out with the ark.

Now for this crap about voltage drop.

It does not matter if you have voltage drop.

If your batteries are low, then you are going to get some form of voltage drop, and this includes when using a DC/DC device which will actually have a greater voltage drop than your alternator will, if the batteries are low.

AND NOW TO MY PET HATE.

I hate the way DC/DC devices are marketed. NOTE I do not hate DC/DC devices, I hate the way they are sold.

Ranga your “ADVISER” was partially correct when he stated “....it is a technical impossibility to charge a caravan battery “ but the correct statement is “It is a technical impossibility to FULLY CHARGE LOW batteries while driving.

And this means you are unlikely to fully charge low batteries while driving, whether you are using your alternator or a DC/DC device.

The reason has nothing to do with the method you use to charge them, they will not be fully charged because it is highly unlikely you will drive long enough to allow the batteries to reach a fully charged state, because low batteries can take up to 10 hours of charging to get them up to a fully charged state.

But if your batteries are low, you are going to replace FAR MORE used capacity using your alternator, than any DC/DC device can replace in the average drive time.

Again Ranga, your “ADVISER” must have been using speaker size wire if he was only getting 2 to 4 amps going into caravan house batteries.

I have measure as much as 63 amps going into 3 low house batteries down 10 metres of 6B&S twin ( 13.5mm2 x 2 ) cable.

Ranga, there are plenty of snake oil pedlars prepared to say anything to try to convince you that you need something you really don’t need.

Originally Posted by drivesafe

Vern, did you get that in one.

Yep, smarter than I look

Originally Posted by Mick_Marsh

The diode he mentioned I assumed was so the battery would charge but not discharge into the system i.e. isolate the feed.

I understand what the diode will do its just any half decent DB setup will isolate the battery ss a diode has nothing to do