Thread: DC/DC chargers, How do they work and do you really need one.

Originally Posted by DiscoMick

Just as an example, our Defender's flow, measured at the dash, just sits constantly on 14 volts.
The Anderson plug on the rear bumper outputs a steady 8 amps. That seems perfectly adequate to keep the camper's 2 x 120Ah AGMs charged.

We have 2 160w solar panels on our 22' Jayco that keep the 2 100AH AGM's charged and I think from memory that they can deliver 12-13A if required.
We also have a VSR fitted on the 79 series which tows the van which on startup runs at a bit over 14v then rapidly drops to mid 13v during the day because the solar takes over But at night or on heavily overcast days it will run at the 14v level for a longer period.
Have you thought of adding solar to your camper to take the strain off your alternator?
You can still have your DC/DC device hooked up to "Take up the Slack" But the solar Will reduce/negate the need for your alternator to feed the system.

I’m at a loss as to why you have the DC/DC at all.

Correct me here but your two 110Ah batteries are in the tow vehicle, yes?

Originally Posted by drivesafe

I’m at a loss as to why you have the DC/DC at all.

Correct me here but your two 110Ah batteries are in the tow vehicle, yes?

If you are referring to myself I haven't got a DC/DC device fitted to either of my 4WD's I only have the VSR's.
I have 160w ridged solar panels fitted permanently to both vehicles in which I have fitted 2x 100AH and 2 110AH respectively.
When on "Float" the readout on the MPPT controllers show 14.2v and when I do a test for SOC they come up at 100% at that voltage.

On the 79 series I also have a 240v inlet so that when we are parked up at a caravan park or if I have to run the genset so that her indoors can have the aircon running the 2x 12v fridge/freezers can run off 240v which conserves power in the 12v system.
All up the 79 series has 4x batteries on board( 2x cranking and 2x house) and when towing the van that goes up to 6x batteries with the 2 in the van added to the system.
This is why I fitted the 2x 160w panels to the van and 1x 160w panel to the canopy of the truck because just using the alternator to keep 6x batteries maintained and charged would put one hell of a strain on the alternator in my opinion

My electrical system may be somewhat unconventional But it works quite well and has been used/tested quite extensively over the last few years and I am happy with how it performs.

Originally Posted by AK83

Ah! AGM as the aux.
Then obviously the MPPT controller would be set to AGM mode, so you wouldn't keep the anderson plug connected as the solar controller will over charge the stater battery.

I’d like to know too as this is similar to my setup, if vsr stays on then both batteries are charged by solar. One AGM so solar controller set to agm mode, main battery is normal flooded lead acid. Is this a problem? Should solar controller be set differently in this setup?

Good explanation from Red Arc. Cheers

REDARC Dual Input BCDC FAQs | REDARC Electronics

Originally Posted by trout1105

This is why I fitted the 2x 160w panels to the van and 1x 160w panel to the canopy of the truck because just using the alternator to keep 6x batteries maintained and charged would put one hell of a strain on the alternator in my opinion

Sorry but no such thing.

You will no put a strain on an alternator through any means.

All alternators, by their very design, are self-protected against current overloading. If a current applied to an alternator is higher than the alternator can produce, the alternator’s voltage automatically reduces.

In any dc circuit, when the voltage drops, the current demand also drops.

You can charge as many low batteries as you need, and if all those batteries are low, causing them all to apply a very large load on the alternator, as above, the alternator’s voltage drops.

As you lower the charge VOLTAGE applied to a battery, the charge CURRENT the battery is drawing, reduces as the voltage reduces, thus lowering the current demand being applied to the alternator.

In other words, the alternator continues to drop until the current demand equals the maximum output current of the alternator, at which point, the alternators voltage levels out.

As the batteries charge, all be it slowly, but as they charge, the current demand being applied to the alternator slowly reduces and as it does, the voltage slowly increases, and this continues until the voltage is back up to the normal operating voltage level.

Originally Posted by JoshV12345

I’d like to know too as this is similar to my setup, if vsr stays on then both batteries are charged by solar. One AGM so solar controller set to agm mode, main battery is normal flooded lead acid. Is this a problem? Should solar controller be set differently in this setup?

As long as the solar regulator is set to an AGM setting, then you can leave the AGM and cranking battery connected indefinitely and no harm will be done to either battery.

If you set the solar regulator to a WET CELL setting, you MUST NOT have the AGM connected or you could end up cooking the AGM battery.

My 101 has an old 55 amp alternator - at times it can have 5 batteries connected to it - I don't even run any VSR - just all connected together when the van is behind it - there are times when the van batteries and the 101's batteries can be quite low but I'm not concerned about the alternator - as Drivesafe said, alternators are self regulating as far as current goes so you can't blow one up by connecting a lot of low batteries to it. The benefit is that instead of the 25 amps a 25 amp DCDC device can supply all your batteries when they need it (Which would take days to charge a few low batteries) your alternator will supply a significantly higher current to the batteries so they will charge much quicker. With your car running along the freeway a more modern alternator (Not my crappy thing) could be letting your batteries draw triple that while they are low and as the batteries come up, they limit their own current draw anyway. Limiting them to draw up to 25 amps could mean you drive all day and still end up with undercharge batteries when you arrive at your next campsite.

It's not like a DCDC device will hurt anything, but I think most of the time they don't actually help with anything or solve any percieved problems.

A lot of the time people make things more complicated than is really needed IMO.