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

That sounds fine to me, as a non-expert.
My 80 watt roof rack panel keeps the starting battery charged very happily through a PWM controller. The charge from the starting battery then flows through the Traxide to the secondary AGM.
I believe having a period of solar charge during a sunny day followed by a period of rest at night is good for batteries, as the excitement and rest reduce sulphation.

Originally Posted by drivesafe

Hi Mick, if your house batteries were in a low state of charge, with 6B&S cabling and that operating voltage, you could see as high as 65 to 70 amps going back to your house batteries.

This would taper off as the house batteries state of charge rises.

Thanks, the auto electrician put 50amp fuses both ends of the cable from the alternator to the Anderson plug for the trailer, so it seems to work well.

Originally Posted by trout1105

I can fully understand that for people that are using only one "House" battery that gets depleted overnight to a low SOC because of excessive use needing to replenish them with the alternator/DC/DC device and this is the most common 12v setup people tend to use But I chose not to go with this setup.

Hi again Trout and I understand that your system works well for your needs, but I am not quite sure what your point is here.


If you have a 100Ah battery and you use 80% of its capacity, you need to replace 80Ah.


But if you have two 100Ah batteries and use the same amount of energy, you still need to replace 80Ah, except now you are replacing 40Ah in each battery.


Similar would apply if you had 3 or 4 batteries, you still need to replace the same 80Ah.


Was there a specific reason or purpose for your statement?

Originally Posted by DiscoMick

Thanks, the auto electrician put 50amp fuses both ends of the cable from the alternator to the Anderson plug for the trailer, so it seems to work well.

Yep, I put 50 amp circuit breakers on all my gear ( with minimum of 6&S cabling being used ) and very, VERY rarely have or hear of problems.

When I first got my D4, I carried out some extensive testing to see if the alternator operation in the D4 would still charge batteries "properly".

One of the test was set up with three smaller batteries placed in the rear cargo area and a 10m long 10mm2 twin cable was used to recharge the three batteries ( total battery capacity was around 240Ah.

While the cranking battery was not discharged at all, before the drive, the three batteries in the rear were discharged down to 20%.

I then carried out a 4 hour drive and managed to get the batteries up over 95%, plus for some time during the start of the drive, the three batteries were doing a constant 63 amps.

Again this was through two 50 amp circuit breakers, and neither tripped.

Unfortunately back then, I did not have the monitoring gear I have now, as it would have been nice to see the whole charge cycle in a graph form.

I have an Anderson plug from car to caravan but no DCDC in van. A mechanic told me this could create a situation where my Freelander 2 could go into limp mode when on the highway? Does anyone know if this is true?

Originally Posted by drivesafe

Hi again Trout and I understand that your system works well for your needs, but I am not quite sure what your point is here.


If you have a 100Ah battery and you use 80% of its capacity, you need to replace 80Ah.


But if you have two 100Ah batteries and use the same amount of energy, you still need to replace 80Ah, except now you are replacing 40Ah in each battery.


Similar would apply if you had 3 or 4 batteries, you still need to replace the same 80Ah.


Was there a specific reason or purpose for your statement?

My point here is that it is my understanding that IF you run a battery down to as low as 20%SOC you can damage it (I could be wrong here) so the extra batteries I have installed (In line) will reduce the amount of depletion "Per Battery".
All I run in either 4WD and the boat is a single 40l fridge and they draw No where near 80AH overnight (More like 30-40AH) so even with a single 100AH battery the SOC will only drop to 60-70% overnight, With two batteries that SOC is much higher.
The 160w panels have No problems putting back the 30-40 AH during the day and this is why I feel that I don't need a DC/DC device to run my house batteries.

The title of this thread is about DC/DC devices and do you need one, I think that I have explained WHY I don't need to install a DC/DC device for MY own personal needs

Hi

My tuppenceworth.

There is a relatively simple explanation at the link below, together with an alternative twin alternator solution which might well work better for people if they don't have aircon and therefore have a space on their engine.

200tdi Defender Engine Twin Alternator Mount, GL1106 – GwynLewis4x4.co.uk

I would have done this myself as I don't have aircon, however unfortunately there isn't a kit for a non-serpentine 3.5 V8...

V8 EFI Twin Alternator Mount, 12V, GL1111 – GwynLewis4x4.co.uk

I think the key observation in the explanation is "The disadvantage to this is that a DC to DC charger can only supply up to about 20amp maximum charging current where as a second alternator can supply 100amps", so I guess the real question would be what you are trying to drive from your second battery. If it a set of low power LED camp lights I can't see a problem. If it is a HD winch, perhaps more so.

Cheers

Alistair

Originally Posted by Teigs

I have an Anderson plug from car to caravan but no DCDC in van. A mechanic told me this could create a situation where my Freelander 2 could go into limp mode when on the highway? Does anyone know if this is true?

Hi Teigs and no mate, if your Freelander is wired up correctly, you are not going to have a problem

To check if there is a potential problem.

Go to your cranking battery, and make sure there is no NEW wiring connected to the NEGATIVE ( - ) terminal on the cranking battery.

NOTE you can have heaps connected to the cranking battery's POSITIVE ( + ) terminal, but nothing other than the factory cabling should be connected to the cranking battery's NEGATIVE ( - ) terminal.

If you are not sure of what you see, take a photo and post it up here and we can help you.