Cheap C-Tek 250S DC to DC chargers

[peril Senior Member Find all posts View Profile Close peril]

I just ordered the D250S at a very reasonable price.

As many know buy reading here on PP, the charge voltage of a 120 D4D is only ~13.5v ave. To charge an AGM to near its full capacity you need 14.4v, that is a gap of 1v that needs to be filled. The price has always been the main factor for me not buying this unit, until now. Just this week the prices seems to have crashed, baintech themselves listed this week $255 for the D250S.

$229.00 from he below link based in Nth Qld with free postage!

http://www.ctek-chargers.com.au/ctek-d250s-dual.html

Those that are looking of one of these now may be a good time to buy?

Hope this helps.

[LeighW Avid PP Poster! Find all posts View Profile Close LeighW]

I just ordered the D250S at a very reasonable price.

To charge an AGM to near its full capacity you need 14.4v, that is a gap of 1v that needs to be filled.

Not correct, as long as the charging voltage is greater than the open circuit terminal voltage of the fully charged battery it will eventually fully charge, ie if the battery terminal voltage is 12.8V fully charged, then 13V will fully charge it, it will just take longer at a lower voltage. That is basic chemistry.

Fitting a booster diode will give a similar voltage at a much cheaper cost.

Cheers
Leigh

[drivesafe Senior Member Find all posts View Profile Close drivesafe]

Fitting a booster diode will give a similar voltage at a much cheaper cost.

And the booster diode will also improve the state of charge of your cranking battery, which in turn will extend the operating life span of your cranking battery, which means the cost of the booster diode is recovered.

Furthermore, the lower your auxiliary battery is when you start your drive, the less chance your new DC/DC device will have of doing any better than what your alternator can do.

Peril, I know you think your are doing the right thing by your auxiliary battery, but you have spent a lot of money on something that will give you little, if any real advantage at the very time you need it, when your battery is low.

[winniliss Avid PP Poster! Find all posts View Profile Close winniliss]

G'day Peril,

I currently run an Optima D27F battery for my cranking an aux battery both of which are in my engine bay. I run a voltage booting diode that gives me a minimum voltage of 13.7vdc (13.9vdc average) at around 32deg ambient temp (live in Darwin). I connect the two batteries using 32mm2 cable and a Redarc SBI12 isolator.

My specs for my battery is as follows:

Open Circuit Voltage (fully charged): 13.1 volts
Internal Resistance (fully charged): 0.0025 ohms
Cutoff voltage (how low I can discharge the battery) 10.5 volts
Recommended charge voltage using an alternator 13.6 - 15v volts
D4D alternator output current is 80 amps

Now my alternator would be able to supply more than 20 amps which is what a D250S can only provide at 25deg. Higher temps means lower amps. As you can see in my situation I would not benefit from using the D250S.

Winston

[winniliss Avid PP Poster! Find all posts View Profile Close winniliss]

double post again...

[peril Senior Member Find all posts View Profile Close peril]

Yes, cross the t's and dot the 'i's', I was not trying to cover 'all' the reasons I have selected this way of doing things. I also plan to run a battery under the bonnet which is against many people advice. I was offering a cheap D250S NOT saying you need to use it for your specific setups. I'm a clever dick too, perhaps I can run a diode and a VSR as well? There is an option for both and all options to be considered specific to the users installation which includes solar options, time to replenish charge, and space considerations. The post was about a Cheap D250S!

Thanks all, I am aware of all the above and much more having been doing this for 40 years myself. Careful consideration of my 'specific' experience and use required for my rig has guided me this way as beneficial in my situation.

How about some simple thanks for the link!

[LeighW Avid PP Poster! Find all posts View Profile Close LeighW]

Hi Peril, For those that have use for one it is a good price and thanks for the post

[pjorek Advanced Member Find all posts View Profile Close pjorek]

i've had the d250s for 3 years now, good unit happy with it. I bought it 2nd hand for that price!

[winniliss Avid PP Poster! Find all posts View Profile Close winniliss]

Or this one for $209 free postage. Have brought from this mob before.

http://www.ebay.com.au/itm/CTEK-D250...053497c&_uhb=1

[peril Senior Member Find all posts View Profile Close peril]

$209 is astounding as well, given the price these were only 6 months ago that's some serious savings.

[drivesafe Senior Member Find all posts View Profile Close drivesafe]

Hi peril and my apologies if my replay seemed to be criticising you for posting up about the price of the device.

My reply was not meant as such, I was just pointing out to you that you had been deceived about the benefits such a device is supposed to offer, decisive by deliberately intended misinformation.

To be precise, it was this quote from you that I was addressing “To charge an AGM to near its full capacity you need 14.4v, that is a gap of 1v that needs to be filled.”

This is the very sort of misinformation that is being used to market these devices.

[peril Senior Member Find all posts View Profile Close peril]

I am comfortable with my reasons and do not feel 'missled', but thanks for the concern. I'm just throwing up some cheap options for those who want to use this unit, discussion on the benefits and drawbacks were had many months ago....

PS forgot to mention, the charge voltage spec I listed was from my preferred Full River AGM battery casing, not Ctek or Redarc propaganda.

Charge voltage spec. is 14.4 - 15v
Float voltage is 13.8v
Max charge rate is 25A

[drivesafe Senior Member Find all posts View Profile Close drivesafe]

Hi peril and I will not comment further on the DC/DC unit, but the specs you posted up for you battery are the MAXIMUM tolerances, not the voltages that are needed.

As LeighW posted, if you check the different battery manufacturers web sites you will get the different charge voltages needed, not just the maximum.

For example, if you go to the Fullriver web site, one of the best for product info, you will see they state you can fully charge your Fullriver AGM with a low as 13.0v

Anyway, enjoy your set up.

[peril Senior Member Find all posts View Profile Close peril]

Hehehe 13v, I laugh because I'm not guna wait for it to charge at 13v, I'm a bit more impatient than that.

More voltage = more current = faster charge (in general terms). Which is very useful when you camp in one spot a few days.

[drivesafe Senior Member Find all posts View Profile Close drivesafe]

More voltage = >>>>>> more current <<<<<<= faster charge (in general terms). Which is very useful when you camp in one spot a few days.

Hi peril and yes you are spot on.

BUT, you have to have both the voltage and the current and this is where DC/DC devices fail to beat an alternator when charging a low battery, even a low voltage alternator will replace the bulk of the used capacity in a low battery quicker than a 25 amp DC/DC device will do.

Peril and please don’t take this the wrong way, I am not having a go at you but you do not understand how these DC/DC devices work.

And mate, that’s exactly what the sellers of these devices want.

Will your device charge at 14.4v, yep it sure will, but what they conveniently don’t emphasis is that the 14.4v charging is only achievable in the final stages of the charging.

This means that if you are just topping a battery off, then yes that device will charge a PARTIALLY discharged battery quicker to around 95 to 97% than your alternator will do, PROVIDING your alternator runs at less than 14.4v

If your alternator runs at 14.4v then it will be the same, and if the alternator runs at higher than 14.4v, it will charge the PARTIALLY discharged battery quicker.

The reason I emphasise “PARTIALLY” discharged batteries is because the only graphs available that show a comparison between the charging of a battery by a DC/DC device and an alternator only ever start with a battery that is only discharged down to just 75% SoC.

If these wonder devices are so good, why is it that these companies never show a REAL comparison between a DC/DC device and an alternator when charging a battery that has been discharged down to a realistic level, say at 50% SoC?

Some more facts. If you have a low 100Ah deep cycle battery, say at just 20% SoC, the level all deep cycle batteries can now be safely discharged to, and you have a 25 amp DC/DC device mounted direct beside the battery, and you have a similar battery with the same SoC but being charged by an alternator running at 13.8v, and feeding the battery down 10m of 6B&S cable.

Which one will have the highest voltage at the battery’s terminals.

The alternator will have a MUCH higher voltage at the battery’s terminals than the DC/DC device will.

You can test the validity of the above info by carrying out the same test and you will get the same results.

And if you fit one of LeighW alternator voltage boosters, you will get an even higher voltage at the battery terminal and the voltage at the battery terminals will remain higher though the the bulk of the charge cycle, if you drive long enough ( which rarely happens, no matter what type of charging you are using ).