Understanding power needs

Hi Carreen,

Please read our blog Electricity for Camping that covers a lot of stuff that will be helpful to you.

To be much help, we'll need to know how big your auxiliary batteries are. Also if you plan to use a dc-dc charger to help with charging them. (All explained in the blog!) Good to see that you understand that hair dryers and such heating gear is NOT suitable for battery power!

In broad terms, your aux battery will probably run the fridge for a day or two. The laptop and some LED lights consume far less than the fridge. Solar isn't cheap and while we use it ourselves, I'd be inclined to include a dc-dc charger and charge from the vehicle. Without the dc-dc charger you will not get a good charge quickly into the batteries. With one, I'd expect you to run the engine for an hour rather than a few minutes each day. This is all very rough and vague because so much depends on how you use your fridge, how big your batteries are, and how well setup you are for charging from the vehicle.

Please read the blog and get back to us.

Cheers

John

Hi Carreen,

You'll need a good dual battery system, generally you'll get 2 - 3 days out of a good system before needing to charge the batteries.

A solenoid system can work very well if installed correctly and is all most users
will require.

You can also use a DC DC charger setup but they are a lot more expensive and not required in most cases, but will keep the autoelects bank manager happy.

You would need to run at idle for hours to charge the batteries so the only real alternatives if 240V is not available to power a battery charger is solar or a generator.

If you wish to run small 240V appliances ie a laptop charger you will need an inverter which converts the 12V DC from your battery to 240V AC, a small 200W to 300W will suffice unless you wish to run that hair dryer:)

As for batteries, yellow tops are great, they are an AGM battery and their designed to be installed in an engine bay, draw back is capacity is only around the 65AH mark.

Other AGM's will give you more capacity but don't like being installed in engine bays.

You should also look at a flooded lead acid batteries such as marine types that are designed for deep cycle use as they have a high AH capacity and will be cheaper than an AGM. There service life will be shorter but generally in a vehicle the physical pounding they receive will kill them first anyway.

As for solar, really depends on how much your prepared to spend.

Best advice I can give is try and keep it simple:)

Hope you enjoy your travels

Cheers
LeighW

Hi Carreen,

some quick figures for your setup:

looking at your 12V loads, the fridge is the big power hog.
It'll use about 3.5A in average, so that's about 85Ah per day.
The rest of the loads are in the vicinity of 15Ah per day, so the total is 100Ah per day.

Alternator charging:
the alternator is capable of recharging the batteries at about 1Ah/minute, but only if they're discharged significantly.
So you'd have to run it for 2 hours every day.
This will bring the state of charge in your batteries to about 80%.

IMPORTANT:
the alternator charging voltage needs to be checked to see if it's suitable.
Take a multimeter and measure across the starting battery a few minutes after starting with the motor revving at mid RPM.
The voltage should reach at least 13.6~13.8V.

Solar panels:
400W of installed power, if no daily alternator use is planned.
So you get about 25Ah from a 100W panel, and the remainder needs to come from the alternator.
How much solar power you install is up to you, but the recommended minimum is 120W for this type of fridge. In combination with a good MPPT solar regulator this panel has the potential to get the battery SOC to 100%, if the alternator charging sessions are timed properly.


Batteries:
2x95Ah deep cycle AGM, wired in parallel to give 190Ah (at 100% fully charged).
This combo will see a depth of discharge of about 65%, based on the 2 hours of daily alternator charging - or a DOD of about 55% based on combined alternator and solar charging.
Solar charging in connection with alternator charging offers the advantage of pushing the SOC to a higher level which is a bonus in terms of battery life expectancy (batteries don't like to be used in partial state of charge conditions for extended periods of time).

Forget yellow tops. This class of batteries isn't really a deep cycle type, and if used in a deep cycle application, they need to be charged following a complex routine. Their $/capacity ratio isn't good either, over $4/Ah, while proper deep cycle batteries typically only cost $2/Ah.

Switchgear and others:
isolation switch between starting battery and house batteries.
Voltmeter to observe voltage/SOC approximation on the house batteries.

Any questions, just fire away.

cheers, Peter

Hi Careen,

LeighW wrote
"A solenoid system can work very well if installed correctly and is all most users
will require.

You can also use a DC DC charger setup but they are a lot more expensive and not required in most cases, but will keep the autoelects bank manager happy. "

This may work for SOME in-vehicle second battery systems, but is increasingly becoming not the case.

As vehicle manufacturers tweak their charging systems to minimise load on engines and reduce fuel consumption and emissions, those charging systems increasingly do not address the charging needs of commonly used second batteries. Consequently, if you're relying on driving time for your car to charge your auxiliary batteries it is becoming more likely that you will need a dc-dc multi-stage smart battery charger to do it.

My 2007 Prado needs one. Your 2007 Rodeo may or may not.

Regardless of the above, if you're using a deep cycle or dual purpose battery in your camper it is almost guaranteed that you will need a dc-dc multi-stage smart battery charger for that battery if you wish to get a decent charge into it while driving. Reason being that with normal standard of trailer wiring there are large losses between the tug's charging system and the trailer battery, and a dc-dc smart charger can largely make up for that. Without t you're kidding yourself.

LeigW alluded to expense - he's right, it's expensive. But personally, I think it's now an expense you must be prepared to accept, especially for your camper.

If you shift camp a lot and rely on driving time to charge your batteries, all this is important.

If you base camp for long periods, then it is less important and solar and/or generator considerations take over.

Whatever your situation, the aim is to keep your batteries as close to fully charged each day as is practically possible, both for practical day-to-day power purposes and for long-term longevity of your batteries. (NOTE: I said "as practically possible". It's not always possible, but within reasonable bounds that should be your aim.)

Don't be fooled - even with an expensive set-up, running the car for 10 minutes won't cut it. Depending on your charging system and the size of your batteries, an hour or more at fast idle would be more like it. Hardly good for your engine - time to think solar or generator.

There are heaps of threads here on this subject. You'd be well advised to search, browse and read them.

Cheers

Frank

Hi Carreen

John and Val beat me to it with their popular blog.

Also Collyn Rivers has very good articles and publications on understanding solar. The following has a list of links on power and solar; the first in the list is to Collyn's website, and the last in the list also his on things you need to know about using power cables.

Setting up and understanding solar power

Motherhen

Thanks to all for your advice! I have printed it off and will digest over the Christmas break. Merry Christmas to all of you! Carreen

There's a good overview at http://www.watts2c.com.au/index.php/faqs.html

you may find it helpful

mh