What is a DC to DC charger??

Yep, good point Bill. I forgot all about that.

Cheers Mick

Hi Bill
Where does the unit acquire the 'voltage' to increase the output from the input???
Me thinks there's a bit of black box wizardry going on here. Similar to the electronic battery isolators- where a $20 mechanical solenoid would do the job, even better as there is no voltage losses as in the 'electronic smart' versions.

Cheers J&D

Wombat, you can get a similar operation by using an inverter to generate 240 V power. You then use that 240 V power to drive a conventional multi-stage battery charger. When you do that you have two boxes that each waste a bit of power (nothing is perfect.)

What a DC - DC battery booster does is to do the same thing as I described above in the one box. It uses only one transformer instead of two (in the simpler units.) As you only have one unit you only have one power loss instead or two. The input stage of the device chops the 12 V power into an alternating waveform, it is only transformed to a sufficient voltage to drive the charging stage and not 240 V like an inverter would.

Yes, the Redarc BCDC1220 will accept input from 9 to 32 volts. See here.
Mind you, it's around $335.

Hiya mate,
What may be the options referred to in yout last paragraph???
Like you, I think I may be a bit sceptical about all the claims of a DC/DC device.

Cheers
J&D

I agree with you Drivesafe, by using big cables and minimising voltage drop, your alternator will give a very similair voltage to your aux battery compred to a dc-dc output and at much higher amps too - though most wetcell batteries won't accept much over 20A anyway.

But the newer temp compensated alternators means often you only get just over 13V in the vehicle so struggling to get 13V to a remote battery in the camper. In these circumstances a dc-dc charger is a great benefit.

Cheers

Captain

You are right to a point Drivesafe. With the high usage I used to have when I had the Kimberley Karavan, it was paramount to recharge the battery pack if I was driving for a part of a day, I could never recharge. The problem was I could NEVER completely recharge from the car. I was battling to get past 90%.

When I put in the Ranox which had the capability to recharge at 25amp/h at say 14.4v volts, I could achieve the fully charged battery and be on float often before lunch time. The Ranox, is no longer available, but has the capability to overcome smaller cable voltage drop, just be re-programming for the distance. It compensated by lifting the charge voltage.

I can recharge my LiFeSO4 battery without internal resistance in quick time.

Hi wombat, and as has been pointed out by both Captain and JohnR, the biggest single issue with a dual battery system, is the cable size.

If you don’t have the correct sized cable fitted, then you are starting from behind.

With correct size cable fitted, you then have a number of options.

Captain raised another potential problem that a number of late model Toyota 4x4s have, and this is their low operating voltage.

When you start a Toyota, the voltage is initially 14+v for ten minutes and then is drops back to 13.2v or less.

This is NOT a temperature controlled operation. You can drive for hours, pull up for fuel, and ten minutes after stopping, with a hot motor, start the motor and the voltage rises over 14v and stays there ten minutes and then again, drops back to 13.2v

A number of European vehicles also have similar but more complex versions of this low operating voltage

While a DC/DC device can resolve this problem for a single battery set up, but because the Toyota system is just a simple timed controlled voltage drop, there is a much cheaper alternative and that is to fit an Alternator Voltage Booster.

This looks like and is a replacement for the ECU’s fuse but it tricks the Toyota’s ECU into thinking the voltage is lower than it is, so ECU cause the regulator to increase the alternator’s voltage to rise up by 0.6 to 0.7v

With a Alternator Voltage Booster fitted, you can now charge ALL your batteries at a higher, more efficient voltage.

The E-mail address is to the guy who developed and manufactures these Alternator Voltage Booster, I might add, they are made right here in Australia.

leigh@hkbelect.com

With decent cable and suitable operating voltages, there is another way to shorten your battery recharging time. If you have the room, fit an additional auxiliary battery.

This may sound strange but an alternator can charge two ( or more ) batteries in nearly the same time it takes to charge one.

Where the advantage comes in is that DC/DC devices will take the same time to replace the same amount of energy use. So if you have one battery and you use say 80 amperes of a 100Ah battery, taking it down to 20% SoC and it takes say 5 hours to replace the use energy using a 20 amp DC/DC device, and it takes an alternator say 5 to 6 hours driving time to get the batteries up over 90 to 95%.

Now if you have two 100Ah batteries and use the same amount of energy, the batteries will only be down to 60% but it will still take the DC/DC device the same amount of driving time but because an alternator can charge two batteries in near the same time it takes to charge one, and because the two batteries are only down to 60% SoC, an alternator can charge them back over 95% in 3 to 4 hours.

But far more important is the fact that an alternator will replace the bulk of the used capacity in the first 1 to an hour and 1/2, where as the DC/DC device will take at least 3+ hours to have the batteries up to the same charge level.

There are other advantages to adding an additional auxiliary battery but this shows there is more than one way to sink a cat.

I agree with Drivesafe except on one point, my 200 cruiser IS a temp controlled alternator. If you start with a warm engine bay, it never gets close to 14V and can be as low as 13.2V. But do the same trip on a cold day and it can stay above 14V for the whole journey.

I do not know about other vehicles, but with the 200 I know for sure its not time based. I have a scanguage and monitor the actual voltage, not the Toyota dash meter.

Cheers

Captain

Hi again, thinking about my post above, I guess that if the problem is simply that with my Toyota, the voltage regulator is set too low to charge the house batteries, there would be adequate current available at this lower voltage to allow the DC-DC device to increase Voltage output, but if the problem is voltage drop due to wire size or length, not sure!

Another sleepless night!!!

Hi

With modern electronics ,it is quite easy to convert voltages & AC to DC or DC to AC
However as you have recognised the Power in will equal the power out PLUS some inefficiecy losses[in the charger]
14.5 v into battery @ say 20amps =290 Watts
To obtain that with an alternator output voltage of 13.2v ,you divide 290 by 13.2 = 22amps
but add for losses & your alternator will be putting out around 24amps<
The Input must always be greater than the output

Peter

Hi
Re :'but if the problem is voltage drop due to wire size or length, not sure!"

Most dc to dc chargers will operate with quite low voltages @ their INPUT terminals[such as can occur with long runs of undersized cables]

However they will have to draw even more current from the alternator to compensate

Taking previous example but with 10v input volts to charger [@its terminals]
290watts divide by 10v =29amps plus efficiency losses [of charger of say10%]
=32 amps

From this you can see that cable size is STILL VERY IMPORTANT

They are not the be all & end all that some seem to believe
Peter