Travel time when a DC-DC charger is definitely required

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@Ctah79
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Travel time when a DC-DC charger is definitely required

Post by @Ctah79 » Wed Oct 18, 2017 5:17 pm

Hi All,

Got a CT with a 100ah battery and 160Watts solar panels.

First trip will be around 5 hours away to an unpowered site and I will have a 60Lt Fridge in the fridge slide to run.

CT doesn't come with a DC-DC to be able to charge it while driving.

I am trying to understand the real need for a DC-DC charger.

Some options I have thought about to avoid running down the battery too much when I get to camp and then having the solar panels not being able to charge the battery. I am trying to save as much as I can now as I just purchased the camper.

Option 1. The night before leaving, run the fridge at home using 240V and setting the temperature to the coldest possible. Then have the fridge unplugged to avoid drawing any battery charge. And as soon as I get to camp and it is set-up, plug in to the CT with the Solar Panels.

Option 2. Run the fridge at home the night before. Plug the fridge while travelling and then get to camp and plug the solar panels. Will I have enough battery when I get to camp or will I run out of battery overnight with the fridge running?

Option 3. Buy a DC-DC charger to be able to maintain the battery charged while driving and the fridge running.

What travelling distances/time warrants the use of a DC-DC charger as a must have?

Thanks in advance for your help.

Andres

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robcaz
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Re: Travel time when a DC-DC charger is definitely required

Post by robcaz » Wed Oct 18, 2017 6:45 pm

Hi Andres,

First up you need to understand how a 12volt compressor fridge freezer works. It does not run all the time, but turns on & off or cycles to maintain the set internal temperature. It is hard calculating the power usage of a compressor fridge as there are so many factors such as the fridges size, the rated power consumption of the motor, the ambient temperature, where the fridge is placed, how many items at ambient temperature are placed in the fridge, the fridges preset temperature, to name a few. The best way to accurately test the power draw of the fridge is by using a watts up meter over a 24 hour period http://www.campertrailers.org/watts_up_meter.htm

Here is a test I did to see what our 40 litre Engel draws at various ambient temperatures http://www.campertrailers.org/fridge_draw.htm As you can see the hotter the day is, the more power required to run the fridge.

If you are camping the weekend, it is a good idea as you have suggested, to put the fridge on the day before with contents & let it chill down. You can also use Techni Ice sheets or similar to maintain the internal temperature if your fridge is not being powered while driving http://www.campertrailers.org/techni_ice.htm

Then in camp you can plug in your solar panel. A 160 watt solar panel will easily maintain your 100 amp hour battery to run your fridge. A little insight in setting up a 12volt system to suit your own needs http://www.campertrailers.org/12volt_system_setup.htm

Where a DC to DC charger comes into its own is when on a touring holiday driving from camp to camp. The charger works as a multistage charger fully charging the battery while driving from the alternator. My thoughts of our Redarc BCDC1225 http://www.campertrailers.org/bcdc1225_feedback.htm

Most DC to DC chargers also incorporate an MTTP solar regulator which is most effective in lower light levels ie of a morning & evening, ensuring you get the maximum current possible at the required voltage at any given point. During low light level situations it will compensate for the low light level and find the new point at which the solar cell delivers its maximum power output. Our Redarc BCDC1225 install with a bit of theory http://www.campertrailers.org/bcdc1225_install.htm

Check the prices at http://www.autoelec.com.au for Redarc, Ctek or Projecta DC to DC chargers.

Hope this helps.
happy camping
Rob & Carol
Australian CamperTrailers Group co-owner


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@Ctah79
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Joined: Fri Sep 29, 2017 10:36 am

Re: Travel time when a DC-DC charger is definitely required

Post by @Ctah79 » Wed Oct 18, 2017 8:38 pm

Thanks Rob for that awesome response. I've learned a lot already.

It looks like I can skip the DC DC charger for this trip. Will definitely put it on the list of upgrades to have.

The only question I have after reading all those nice articles is that the DC-DC charger comes with an in-built MPPT regulator.

My solar panels already come with a MPPT regulator.

What will happen once I get the DC-DC charger? Can I plug the solar panels into the charger?

Is the double up of regulators an issue?

Thanks again Rob

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robcaz
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Re: Travel time when a DC-DC charger is definitely required

Post by robcaz » Thu Oct 19, 2017 7:53 am

Hi Andres,

You will find the inbuilt MPPT solar regulator in the DC to DC chargers will most likely be of far better quality than those on the rear of most solar panels, depending on the brand of solar panels of course. You can just bypass the solar regulator on the rear of the panel so you have unregulated output to the DC to DC charger. You can drop me few photos of the regulator showing connections etc to ownersATcampertrailers.org (replace AT with @) & we can have a look at the best way to go about it.

Keep the regulator attached to the rear of the panel as it may come in handy to charge your vehicle battery or perhaps someone's camper trailer battery.

On the other hand Redarc's BCDC1220 is just a straight DC to DC charger which only connects to the alternator. You can then connect the MPPT regulated output straight to the battery.

You do need to know if your vehicle has a smart alternator, ie has a variable voltage output. While some DC to DC chargers are dedicated high alternator or low alternator output compatible, some only require a wire to be installed a certain way to change the output.

We have found the 10 metre of 6mm auto twin core sheathed cable a very handy length, from the solar panel to the DC-DC charger, following the sun during the day & avoiding the shade. With the unregulated panel output & the MPPT regulator at the battery there is very little voltage drop over that distance.

Hope this helps.
happy camping
Rob & Carol
Australian CamperTrailers Group co-owner


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Ern_Reeders
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Re: Travel time when a DC-DC charger is definitely required

Post by Ern_Reeders » Wed Dec 06, 2017 6:46 am

And here's some more data on fridge (and other device) consumption: http://12voltblog.com.au/how-much-power ... stuff-use/

You'll see they can draw quite a lot. If the weather is bad or you're forced to camp in shade, it's possible to empty the 'bank' quite quickly.

As for DC chargers, the Projecta has some advantages: temperature sensing and push button selection of battery type. You get some benefits by installing such a charger next to your battery.

Good luck.
Cheers, Ern

Pioneer Argyle SE and Isuzu MU-X

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