12v dc/dc chargers

Hi spudboy and before you part with your hard earned cash, do some research on what is fact and what is nothing more than good old fashion advertising hype.

First off, that’s a really good idea of having a temperature sensor, you would think.

Problem is that the cranking battery doesn't have a temperature sensor and as it is on a constant charge, why then does it not cook itself?

Next, and something I have continually ranted about and that is why there is never an actual graph to show just how long one of these devices will take to bring a low battery to a fully charged state.

Just saying these devices will fully charge a battery is just not good enough.

How long does it take to bring a small battery to a fully charged state and then how long does it take to bring a large battery to a fully charged state.

Something they never mention is, what happens if you find your single auxiliary/house battery is not big enough to meet your requirements so you add another battery?

Can these devices fully charge “A” battery, can’t see why not, “IF” they are given enough time, they can charge any size battery or bank of batteries.

The problem is, are you actually going to be driving long enough to allow anything to fully charge your batteries?

These devices, contrary to the claims made about them, they are not the only way to get batteries charged and there are cheaper ways to achieve better results.

As for the video, remember, thats a salesman trying to sell you something that you probably don't need!

Some choices here:

DC Battery Chargers - get the right advice

I'm using this Engel one:

Engel Australia - Portable Fridge-Freezers

The retail price is $170 but I got mine from BCC for only $70 on sale last year.

The amount of charge varies between units. For example the Redarc does 40ah, while others do 20ah. Engel simply says the time to charge will vary but is usually within a day's driving, whatever that means.

Another issue is whether you merely want a charger or if you want a battery management system including a charger.

Also, do you want to be able to charge using a solar panel? Some, such as the Redarc and C-Tek 250s will do that, but others won't.

Quote:

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Originally Posted by drivesafe

Hi spudboy and before you part with your hard earned cash, do some research on what is fact and what is nothing more than good old fashion advertising hype.

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Well, the reason I went with the CTEK is because I have one of their battery chargers, and it has been brilliant, and as well I wanted to have a solar panel as input, so things kept charging when the engine was off.

For me it conquered 3 issues in one simple to install unit:
- Isolates the fridge battery when not charging
- Allows solar panel input, and balances the charging between the alternator and the solar panel automatically, and I didn't need to get a separate solar regulator. No switches to go between engine/solar charging
- DC-DC charging of the remote battery

Do you think there is a problem with their quality or something?

Cheers
David

Yeah, I've heard good stuff about the C-Tek 250s. Seems to be cheaper than the Redarc too, although the charging rate appears to vary between them.

Our Engel is not a battery management unit, but a simple DC-DC charger to boost the charge from the vehicle before it goes into the battery in the camper trailer while driving.

I'm thinking about replacing the simple battery isolator in the Disco with a better unit such as a C-Tek, so it will boost the charge around the vehicle, manage the batteries and take solar power.

To the OP, it really depends on whether you just want to boost the charge in your camper (Engel will do that cheaply) or if you want to manage all your batteries, also charge them and take solar power, when you need something like the C-Tek or Redarc or similar (Traxide etc).

Hi again Spudboy and from memory you have an early model L322, if so then your alternator runs at 14.3v, day in and day out.

This is way high enough to charge any number of batteries anywhere in your RR or in a caravan or camper trailer.

A DC/DC device, no matter what the brand, is not going to be of any real benefit to you ( if any at all ) and as posted there are better ways to do what you want.

If you are after fast charging times, then my SC80 allows much shorter recharge times plus it gives you more usable capacity and at a fraction of the set up cost.

As for solar, again the SC80 allows solar to charge all your batteries, not just one.

In the future, are you likely to need more battery capacity?

Thanks for all that DriveSafe - this is used in my 2001 Defender 130, not the L322, if that makes any difference.

I am charging 2 x 75Ah Optima Blue Top Marine batteries connected in parallel on the Fridge/Accessories side of things, and another separate Optima for the starter battery.

From memory (I did this a year ago) I ended up with 2 accessory batteries together to get enough Ah (?). From my calculation I wanted 120Ah and the biggest Optima I could get was only 75Ah, hence 2 in parallel which should give 150Ah.....

Edit: BTW - I think the solar input charges all batteries, not just the fridge ones.

Next time you are driving, with the motor running, do a voltage reading at your cranking battery.

Anything over 13.6v is going to give you good charging.

With all the batteries you have and the fact they are Optima batteries, ( quick charging batteries ) any DC/DC device will actually take much longer to charge them if they are low.

As posted above, do a fair bit of research and I will be very surprised if you still think a DC/DC device will be of any benefit to you and once you do the math, with low batteries, you will probably take heaps longer to charge your batteries than if you just let your alternator do what it is designed to do.

Hi Spudboy and one other point I overlooked.

Try not to compere battery chargers with DC/DC devices.

While they both work in a similar fashion, when using a battery charger, you usually have plenty of time to allow the battery charger to perform it’s different cycles and this is where they can do a good job of charging a battery better than a alternator can.

The exact reverse is the case for DC/DC devices where, because they are rarely given enough time to fully charge batteries, they achieve little if any advantage over what your alternator can do.

This is again where your set up, with fast charging Optima batteries, is going to benefit from the ability of your alternator to deliver high current for charging.

Quote:

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Originally Posted by drivesafe

.........................................they achieve little if any advantage over what your alternator can do.

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At the risk of asking a totally stupid question. What is the point/advantage of a so called 'DC/DC device' ?
I've followed this and other 'World of Batterycraft' threads through all the pain and anguish but still cannot see the point.
As far as I can tell a 'DC/DC' device is one that turns a lower DC voltage into a higher DC voltage and then (because of its componentry) current limits charge to a battery at this higher voltage. What's the point ?
If you have an older vehicle whose alternator delivers say 13.2 V (my old RRC) and you have Calcium/Calcium battery(s) whose optimum voltage is say 14.6 V wouldn't it be easier/cheaper to change the alternator/voltage regulator instead ? And if the existing alternator delivers this voltage already why would you want it higher ? In another thread voltages of 15 V + were quoted. Why would I want to subject my vehicles battery/electrical system/electronics to this voltage in a nominally 12 V vehicle ?
Seriously, what am I missing here ? Is it about running a higher voltage so that battery(s) in a caravan/camper can overcome voltage drop and charge OK ?
I'm not a big believer in complex charging systems at the best of times but am totally bemused/amazed at how the relatively simple task of effectively charging a battery(s) can be made to appear so complex.

Deano:)

Hi Deano and the theory behind these devices is sound, and some of you will be surprised to see me posting that but the principal is sound.

What is not well covered, or more accurately, what is totally ignored by the sellers of these devices is that in most cases people never drive long enough to get any benefit from these devices.

If you are just topping a battery up, not a problem, these devices will do a better job than your alternator can.

But if your battery is never used that much that you can continually top it of, whats the advantage when the battery is not being used to it’s full potential anyway.

I know I have ranted about the lack of any form of time line being provided by the manufacturers/sellers of these devices but with out this info, one can not make a credible assessment of the true value or lack of value these devices offer.

Ctek have a graph displayed in a number of their brochures but again, while it looks great, it has no time reference so the graph is nothing more than an advertising ploy used to help to “IMPLY” their gear does a better job.

Another company, Ranox, use to say on one page that you could drive from Perth to Sydney and your alternator will never fully charge your house batteries.

Then on the very next page they had a TIME based graph where they claimed their DC/DC device will charge two 100Ah batteries from 75% SoC to a fully charged state in 150 minutes where an alternator would take 180 minutes to fully charge the same batteries.

Now the first problem is that the graph only covered charge batteries from an SoC of 75%. This means if someone never took the two 100Ah batteries below 75% then they only ever used 50 amperes of power.

So why the hell then did they have two 100Ah batteries in the first place when one 100Ah battery would have easily met their needs with out having to discharge that single 100Ah battery below 50% SoC.

Next, the reason their graph started at 75% is because they knew the DC/DC device would charge quicker than an alternator, whereas if they had shown the graph starting at just 5% lower, you could literally flip a coin to see which would fully charge the batteries first, the DC/DC device or an alternator.

If the graph started from 60%, it would show an alternator would easily charge the two batteries quick. From 50%, an alternator would beat the DC/DC device by at least an hour and from 30% and alternator would beat their device by a number of hours.

This is the sort of deceptions used to sell devices that most people will probably get little to no benefit from and will certainly not get anywhere near value for money.

BTW, the Ranox device is no longer available!