Charging the battery in camper/caravan

I haven't disregarded the cable issue ... but I dont really want to have to use excessively large cables to avoid a voltage drop, when there may be a practical alternative such as a DC/DC booster at the camper end

Hi Drew T, I’m with Alex on this one.

You quite obviously think that the direct off the alternator charge is inferior to your other to options when quite the revers is the case.

Using either a 20 amp DC to DC charger or an inverter / 20 amp battery charger will charge a fairly well discharged battery up to a size of about 70 A/H quicker than straight off the alternator.

It’s about even steven for batteries up to 100 A/H but once you start to try to charge a 100 A/H or bigger sized battery it is going to be achieved quicker straight off the alternator.

Now the first this your going to say is you can use a bigger inverter / battery charger set up or what ever, true but now you have to run much larger cable and the larger cable by itself can still charge the battery quicker.

There’s a whole host of conditions that have to be considered but just fitting 6B&S cable, installing 2 two 70 A/H batteries and starting out with low batteries, at the end of a days driving, even if its only for three or four hours although they won’t be fully charged, you are still going to have far more stored capacity.

The problem is, most people are so dazzled by technology that they actually loose the plot. The aim is, at the end of the day, to have at least as much stored battery capacity to meet your needs and this can, in almost every case, be done cheaper and far more reliably by simply fitting suitably sized cable and two auxiliary batteries in stead of just one and unlike all your hi tech so called solutions, your alternator can deliver better and more charge.

Cheers.

As DS says it's a lot cheaper to use the correct sized cable in the first place.

Remember that AGM's will recharge much faster and more efficiently than wetcel batteries also, this is important when you are not doing many hours of driving each day.

Mark E , yep Collyn wrote the bible on 12v but all is not gospel , each and every application is different , in mine I have 8mm sq tinned copper running from the aux batt to the rear bumper mounted anderson plug , voltage drop is 0.01v , same size cable to the c/tbatts and voltage drop from front of vehicle to c/t batts is still only 0.01v , quality of connections ,wire size and meticulous attention to detail overcomes drop in 12v.

Mark E , yep Collyn wrote the bible on 12v but all is not gospel , each and every application is different , in mine I have 8mm sq tinned copper running from the aux batt to the rear bumper mounted anderson plug , voltage drop is 0.01v , same size cable to the c/tbatts and voltage drop from front of vehicle to c/t batts is still only 0.01v , quality of connections ,wire size and meticulous attention to detail overcomes drop in 12v.

Is that voltage drop measured under load, whilst the camper battery is sucking in 40-50 amps from the alternator? Correct me if I'm wrong but voltage drop varies with current? ie greater load = greater voltage drop? No expert obviously......

Cheers,

Mark

Axel

"voltage drop is 0.01v" at what current???????????????
Were you running any real equipment at the anderson plug end of your setup when you measured? If not then your voltage drop should be 0.00v with any gauge wire.

Nev

Not an expert either , but show me a battery that will accept 50 amps and I will by it , , voltage drop from front to rear [ l/cruiser 80 series t/d] in my application of 80amp fullriver agm hgl as starter and same type batt as aux thru a redarc copy then to c/trailer as described earlier to 3x 80amp fullriver agm hgl batts , the only voltage drop is 0.01v front to rear.

Scubadoo , it matters not 1 iota whether I have the motor running / the 2 fridges plugged in and running or everything switched off my voltage drop or for a better word variance front to rear is 0.01v , no not perfect I know , but at least it bl--d- well works and has done for years.

According to the calculator at lcool the voltage drop is more with greater current, eg, my setup with 32mm cable running 30 amps the drop should be 0.01v, lesser current didn't register at all...

another option I am thinking about is a 2-3hp motor and putting an alternator on it, you can get these off the shelf for $6-800 but that wouldn't be as much fun, these would be good for base camping, they do from 55amps up, same charge rate as 10-12 solar panels!!!

NickR

"I have some old unused welding cable that I plan to run which is about 25mm sq and accept that the batery will never really reach full charge whilst on the run. "

Not true (provided there is no heavy draw from a fridge). As the battery charges, the current decreases and the voltage rises. If you drive for long enough the trailer battery voltage will be the same as the front battery.

I don't need to do the maths. Hundreds of websites can e.g.
http://www.stealth316.com/2-wire-resistance.htm

Nev

That should read "it's NOT that hard to keep charge up to your camper battery"

But I dont carry a coffee making machine , LOL , instant in the scrub will suffice ergo the K.I.S.S. principle , [ a decent slug of scotch makes any coffee great] LOL.

I do, but it's a stove top espresso/cappuccino maker, LOL

One thing about the inverter to battery charger, this is only a BACKUP as it's not really that efficient, i have used it a couple of times and it can take a long time to charge the battery in the camper, ALSO i don't think it would fully charge it.

Baz.

You are so right Derek ..... KEEP IT SIMPLE.

I can't believe the incessant discussion here about batteries, for the past 2 years I have been using a Delkor Calcium battery in the CT, using 6mm cable & only the 7 pin trailer plug & have never had a problem.
I would never contemplate buying $300 or $400 AGM batteries that may, or may not last a little longer, but I can buy at least 2 Delkors for that.

Hi Garth, you will now actually take longer to charge your batteries than if you had just run some decent sized cable from the vehicle’s battery to the van’s batteries.

Just running 4B&S cable will give you a 40 amp charge at 13.8 volts. If your batteries were at about 50% when you started to drive, which means they need around 180 to 190 amps to fully charge them, you will put about 100 amps of bulk charge back into the batteries in around 3.5 hours while your charger is going to take around 5.5 hours to do the same.

Furthermore , if your batteries are lower, the the time difference is going to be even longer using the DC to DC charger as compered to just charging the batteries from the alternator.

Even if you used thinner cable such as 6B&S you are still going to be at least an a hour better off, when using the same comparison.

Either way, you are going to need at least 10 to 12 hours driving to get all those batteries from 50% to anywhere near fully charged.

The math just does not add up to use these devices on anything but the smallest battery set ups and yours is anything but small.

It would have been far more advantages for both you batteries and you pocket if you had simply fitted thicker cables.

Cheers.

Have to agree with Drivesafe and Redback.......kiss...kiss...!!

Assuming you have only used 10% capacity overnight, your alternator will have no trouble topping up the batts...
And sorry to say....when you paid all that money for the Karavan...a 80 to 100W solar panel mounted to the roof would have been a far more useful addition than a dc/dc regulated power supply thingy !!
And with a solar panel, you may find that the batts are nearly fully charged all the time....

thanks Garth. since you own a Kimberley Karavan would it be possible to scan & email me a copy of the wiring diagram from your user manual?

The physics are inescapable - a thin cable and an Inverter will always have more losses than a thick cable.

DC/DC power boosters are useful for running high-powered transmitters when the engine is off, because transmitters usually won;t put out out full power below 13 volts.

I could find no info on this unit on the Motormate website - where did you get it from ?

Mike,

Try
www.electroparts.com.au

Got it through an auto elect mate as they don't sell retail.
$195.00 including delivery.

Boy has this discussion generated some power!!!!!

Cheers
Garth

Drivesafe,

Have cable of 13mm^2 twin running from anderson plug to second battery in the vehicle.

This device is about supplying a constant 13.8Vdc to 10 off 35A/h batteries with a C20 rating. They are in a parallell configuration.

They are exide ED 10S AGM deep cycle batteries.

Unit is mounted in Karavan within 1 metre of batteries. (most practical position)

Cheers
Garth

Hi Grath, I’ve seen how the Kimberley’s are set up, including the large battery banks.

I’m not saying you shouldn’t do it, it’s just that you are now going to be supplying less current to the batteries than an alternator can easily do by itself and as such it is not only going to take longer to charge them, it’s unnecessary.

Also if you have a look at the rest of the set up, you can actually cut a fair amount of wasted power usage and in doing so, not have to discharge your batteries as much in the first place.

Cheers

Anderson plugs (small size ) are rated at 50A..

I run a 12 pin plug and double up the pos and neg pins to achieve a rating of 70A !!!

Just thought I'd add that as there are lots of diff ways to run power to the back of the 4x4 !!

Hi Gronk, trailer plugs can be used but you must be careful when using trailer plugs because the rating is their continuos current capacity once connected BUT in automotive applications anything that is used to switch or connect power should have a Make & Break rating.

For instance, a 40 amp headlight or horn relay’s rating is based on the maximum current the contacts of the relay can tolerate during the turn on and off operation ( Make & Break ).

Higher currents can be carried ( but not recommended ) while the relay’s contacts are closed but you can only switch up to 40 amps with out damaging the contacts.

Trailer plugs are designed to be connected and disconnected in a NO LOAD situation so virtually any currents present while connecting or disconnecting, will start the burn the contacts in a relatively short number of operations.

Anderson plugs on the other hand are actual specifically designed to be able to be connected and disconnected at least 250 times at their maximum Make & Break current rating ( 50 amps ) and the arcing that occurs will only have minimum effect and while connected can tolerate current surges of up to 200 amps for a few seconds.

In a NO LOAD situation, Anderson plugs are designed to handle around 10,000 Make & Break operations before the contacts actually start the ware.

So try to avoid connecting and disconnecting your trailer plug while the motor is running and may give your plugs a longer operating life.

"Anderson plugs (small size ) are rated at 50A..

I run a 12 pin plug and double up the pos and neg pins to achieve a rating of 70A !!!"

That may be fine in a laboratory, but in the real world there's dirt and water.

Anderson contacts are silver plated but trailer connectors are brass - after a while the brass contacts will have higher resistance and produce self-heating which will weaken the contact.

Yeh, I know, but it's so easy to have only one plug ..

But the rare times I actually use the charge cct ( most stays are only for a weekend ) the 6mm2 cable running directly off the normal battery thru a 40A relay ( switched from the dash when the normal batt gets up to charge ) usually only draws approx 10 to 20A ( except for initial inrush )

But the easiest way to avoid excessive current is to not flatten the batts too much before recharging... always better to top them up instead of doing a full charge up !!

With that set up you shouldn’t have any problems as you control the currents when connecting and disconnecting.

Cheers

Yep, always easier to top up the batts rather than trying to charge them from flat..

I don't "maintain" my AGM's at home because I don't need to !!!

Put them on charge (3 stage charger ) when I get home,disconnect when charged, then forget about them until I go camping again..
Well, I do sneek a look at them occasionally with a multimeter, but they are always 12.9 or 13V

Yep, always easier to top up the batts rather than trying to charge them from flat..

I don't "maintain" my AGM's at home because I don't need to !!!

Put them on charge (3 stage charger ) when I get home,disconnect when charged, then forget about them until I go camping again..
Well, I do sneek a look at them occasionally with a multimeter, but they are always 12.9 or 13V