brian wrote:

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[1]Oldtrack, your last 2 posts certainly contradict each other. Firstly you suggest to me that any voltage drop over 0.5v requires a rewire rather than a DCDC charger, and that it is acceptable for such device to not boost from a voltage lower than 12.7v, then you tell Plendo that unless the device can do just that then it is a waste of time. Wow.

[2]Just about every charge system out there would have a voltage drop greater than 0.5v when and if full charge current could be achieved. Incidentally, I have not changed my story one bit. If you go back to my very first statement on this subject, I said, quote.

3]"The ctek 250s dual is not a DCDC charger in the accepted sense as it does not have the ability to boost the output voltage above that of the input as do true DCDC devices ". This is a perfectly true statement, and one which I have maintained throughout this discussion. As for going to even l

[4]ower voltage.. Many do just that... Stirling, who do call their device a DCDC charger go down to 8v and Leab, who call their device a DCDC booster have one that goes down to 7.5v. I have to wonder why they would bother investing so much time and cash into these devices if, as you say, they are unnecessary, and why go down to such low voltages if again, as you say, that is not required. If you and others choose to call a DCDC charger such simply because it has both a DC input and a DC output, then go right ahead, I have attempted to expose the shortcomings of this particular device here, and will leave it at that. I will also point out that your comment to Plendo that unless the DCDC charger could boost the voltage from below

[5] battery voltage then you may as well stick to straight alternator charging is completely erroneous. Any good auto elec knows that the reason straight alternator charging a remote battery is inefficient has to do with the fact that

[a]the regulator will ramp the alternator output down unless it sees sufficient load not to do so.

b] A DCDC device provides this load, a remote battery does not.

[c] Even the ctek unit will achieve this result and so be better than a straight alternator charge.

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HI Brian

[1]

The statements do not contradict each other

Nowhere did I suggest to Plendo Any voltage fig

What I did say is that the Crek IS A VOLTAGE BOOSTER, WHICH IT IS,

It WILL BOOST 12..7 V to 14PLUS volts to fully charge the house battery!!

THAT is what the MAKERS CLAIM  & users have consistantly found

My post to Plendo said that IF they do not do THAT, they were a waste of time, BUT THEY DO BOOST  despite your inablity to accept THAT

[2]So you still suggest that a 25<27% loss of voltage is OK???

That could result in a sinificant %loss of alternator AVAILABE power

AS you know voltage drop is relevent to current ,cable SIZE  & run length 

0.25<0.5V drop at 30A is quite practical & ,before the new model cars with lower alternator voltages  was a  common requirement for direct charging!,

Even today with   figure 3way fridges & the new vehicles  0.5V Drop is about the max if the fridge is to operatet well.y on 12V .

 How is that achieved ? by correctly sized cables!

You are falling for  [& suggesting others do the same,]  the marketing trap of many DC /DC charger sellers , overcome voltage drop rather than FIX the CAUSE

[3] Again you repeat THAT  please open your eyes  .IT DOES boost. But it limits the lower limit to maintain the crank battery in a high state of charge

IT boost from 12.7V up to 14plus volts

 IT IS A DC DC CHARGER IN EVERY SENSE OF THE WORD

What protection does the the crank battery have from over discharge with a unit that will run down to 9.6V ??????

It is not intended to charge one BATTERY from Another BATTERY[if that is what you consider is required of a "true " dc to dc charger

IT IS INTENDED TO BE USED with ALTERNATOR.

[4]ALL They do is operate to a LOWER input voltage

THEY are not required to boost any higher than the Ctek or others

  Why they designed them that way , Simple answer to overcome EXCESS voltage drop DUE TO INADEQUATE CABLES!!but again it seems you are happy with such  cables that have up to27% voltage drop

But they leave the crank battery exposed to possible over discharge ,NOT a good idea ,IMHO

[5]Auto electricians would be the last source I would think an elecrical engineer would be quoting

And  Ifind much of this part confusing

A lot of your remarks are only relevent to those vehicled which reduce the ALTERNAOR voltage to 13.2Vapprox   

IT certaninly does not aply to the majority of vehicles on the road

  Direct Charging can be quite successful if the voltages drop between batteries is limited

It may not allow the a remote battery to fully charge, but in the case of say a motor home where both batterries may be side by side it sees them simply as a paralled bank & charges EACH to the same SOC

[a]An alternator is voltage regulated it responds to  voltage [The SOC voltage of the connected batteries ]

Although its voltage can be depleted by other heavy loads

A dc / dc charger does no more than boost the available the voltage, & regulate the charge ,  but the alternator must have the POWER avialable to supply the higher Amps input  required

[c]IS THAT an admission the the Ctek is a boost unit???

PeterQ

-- Edited by oldtrack123 on Thursday 9th of January 2014 12:38:09 PM