Sunday, Feb 09, 2014 at 23:11
Steve,
First point that I will make is that the Ctek unit is not recommended for use on low alternator voltage vehicles due to its relatively high cut-out point, all other brands seem to be able to handle the lower voltages quite
well.
Contrary to what is being said on this thread, DCDC chargers such as the Redarc etc. compensate very
well for line losses.
Here are the comparative figures of a
test that I recently carried out in response to another such thread on this
forum.
The figures are accurate but you can bet they will be disputed by the die-hard direct alternator charge dinosaurs
Sorry about all the dots and dashes but it seems to be the only way to get a chart on here.
The vehicle is a 100 series Land cruiser with 110 amp alternator.
Charge cables are 2 metres long 13mm2
The 2 crank batteries are in normal charge condition.
There are no accessories in use to stress the alternator or prevent it from outputting a decent current.
The auxiliary battery is a Century Marine Pro 600 in good condition, it is a hybrid battery so will accept a faster charge than will a normal flooded deep cycle battery.
I have used a flooded battery so that specific gravity readings can be taken to determine true Soc more accurately than can be done by simple voltage readings.
It has been discharged to a rested voltage of 12.18v which is approximately 55% Soc
Specific gravity reading of 1.170 which is a tad under 50% Soc
......................... Time...............Crank V.................2nd Battery V..........Chg Amps
Engine off.............10:30.............12.86........................12.18.....................0
Connect 2nd bat....10:33.............12.80.........................12.25....................2.10
Engine running......10:34.............14.10........................12.78...................14.50
----------------------10:35-----------14.09---------------------13.09----------------12.30
----------------------10:40-----------14.08---------------------13.30----------------10.90
----------------------10:50-----------14.04---------------------13.34----------------10.10
----------------------10:55-----------14.02---------------------13.36-----------------9.80
----------------------10:00-----------13.97---------------------13.35-----------------8.32
----------------------11:10-----------13.97---------------------13.36-----------------7.00
----------------------11:30-----------13.97---------------------13.40-----------------6.22
Specific gravity reading of 1.175 indicates Soc to be a bit over 50% which is not much better than where it started
Charge terminated and battery connected to Redarc BCDC1240 set to Std LA
Engine off----------11:40-----------13.84---------------------12.86-----------------0
Charger goes straight to Absorption mode, not expected, and not sure why.
-----------------------Time----------Charger V------------2nd Battery V...........Chg Amps
Engine running----11:45------------14.70---------------------14.40----------------25.86
----------------------11:50------------14.70---------------------14.43----------------23.70
----------------------11:55------------14.70---------------------14.44----------------21.35
Charge terminated.
Demonstrates that the DCDC charger is able to put in around 4 times what the direct alternator charge was able to do even after the alternator had been at it for an hour.
Total charge put in by alternator in one hour, about 10 Ah.
The charge from the alternator, which has the ability to provide 110 amps, never got over 14.5 amps into a battery which the DCDC charger proved could still take at least 25 amps even after 1 hour on the alternator.
Battery discharged back down to 12.07v, rested for 2 hours and began another charge on DCDC charger.
--------------------------Charger in Boost Mode
--------------------Time--------Charger V-------2nd battery V----------Chg amps
Chgr off-----------3:00------------0----------------12.07-------------------0
Chgr on-----------3:01-----------13.90------------13.44------------------35.90
---------------------3:03-----------14.10------------13.65------------------34.86
---------------------3:04-----------14.20------------13.66------------------34.65
---------------------3:05-----------14.20------------13.66------------------34.45
---------------------3:10-----------14.40------------13.84------------------33.53
---------------------3:13 Charger goes to Absorption mode
---------------------3:14-----------14.60------------14.15------------------32.76
---------------------3:20-----------14.71------------14.35------------------29.70
---------------------3:40-----------14.70------------14.34------------------17.90
---------------------4:00-----------14.72------------14.46------------------15.17
Charge terminated.
Demonstrates that DCDC charger inputs considerably more amps to the second battery than does the direct alternator method.
Total charge put in by DCDC charger in one hour, about 25Ah.
Disconnected battery terminal voltage now at 13.83v which would appear to indicate a good Soc, but specific gravity reading of just 1.195 indicates true Soc to be just 60%.
Battery voltage 3-1/2 hrs later at 7:30pm is 12.8v (100% Soc?) but S.G. of 1.225 indicates only 75% Soc.
Battery voltage next morning is 12.55v, S.G. is 1.240 which is consistent with about 80% Soc.
This is due to surface charge having been absorbed into the plates overnight and shows the importance of rested voltage measurements, and the folly of assuming your battery is fully charged just by a high voltage reading.
A few points can be seen from these figures.
1. The Redarc DCDC charger does not stay at a constant current until the battery reaches 80% Soc, in fact, it has dropped to roughly half the original current by the time the battery reaches 60% Soc.
Why is this? Simply because the opposing voltage of the second battery has risen due to surface charge absorption delay.
2. The Redarc DCDC charger has reached 14.4v within 10 minutes of beginning its charge, not 3 hours as has been suggested. At this stage the battery is still at less than 60% Soc, not 80% as has also been suggested.
3. In the first chart, the alternator output voltage remains fairly constant within a range of 0.13v. A diode fuse would realistically add 0.6v to the output which could conceivably add a few more amps in the early stages until the crank battery voltage rose to that level or temperature compensation/ECU controls cut the voltage back again.
For alternator controlled vehicles where the voltage can fall
well below 13v, even the diode won't help much as the figures would again be similar to or less than those shown.
The results are repeatable for anyone who wishes to do the same
test.
The doubters can bitch all they like, the
test was done honestly, the figures are up there, and I am not interested in getting into a debate about it.
AnswerID:
526102
Follow Up By: Dennis Ellery - Sunday, Feb 09, 2014 at 23:36
Sunday, Feb 09, 2014 at 23:36
Yes Brian these figures are credible - I too have done similar tests.
The advantage is even greater when charging a battery at the end of a long connection such as in a caravan.
I haven’t bothered to list my results on this post as many wouldn’t understand them or either wouldn’t take the time to decipher the data.
FollowupID:
808250
Follow Up By: The Bantam - Monday, Feb 10, 2014 at 11:50
Monday, Feb 10, 2014 at 11:50
Firstly.
The time taken with this
test is not long enough...it is not even a full charge cycle.....this brings into question the validity of the
test.
One or two hours...of for goodness sake.
Second
Any advantage the DC to DC charger may have, can easily be attributed to the terminal voltage of the charger and nothing else.
You terminate your
test with the alternator charged example with the battery at 13.4 volts...you terminate your DC to DC exampe at 14.4 volts...A FULL VOLT DIFFERENCE.
Third.
I gather this vehicle was not driven, but sat there at idle.....hardly giving the alternator a fair go.
I have curves for the alternator in my vehicle, it shows it does not produce rated current output ( 100 amps) till a shaft seed of 5000 rpm, that equates to an engine speed of arround 2500 rpm on my vehicle. At engine idle speed of arround 600-800 rpm its output is arround 30 to 50 amps.......by the time vehicle electrics load and charging losses are factored, you woul be lucky to be putting 15 amps into the battery.......Hmmm funny that...that is what you measured.
Fourth
You point to specifc gravity and beeing a more accurate indicator of charge.
You have not accounted for the variations in acid SG in the battery during the charge process.
It is
well known that the SG of the acid varies thruout the battery.....the SG will increase at the top of the battery and remain low at the bottom of the battery PARTicularly at low charge rates.
Its called acid stratification.
So unless the battery is mechaically agitated...like it whould while driving, is vigorously charged thus creating agitation from gassing or is left to equalise..for some time.
Reading of SG taken at the top of the acid pool will be very inaccurate.
We where drilled on this when I was an apprentice.....we logged SG and voltages on large battery banks weekly.....and we where required to rest the batteries before measuring either.
AND we used big ass chargers that would produce enough charge current to agitate the electrolite.
Then there is the question of condition of the battery.
I have a marine battery that if left idle will not accept much charge, and will take at least 2 days to produce a "fully charged" light on my 7.5 amp multistage charger and only then when the charger is switched to boost mode at 14.5 volts.
discharged and recharged a couple of days later it recharges much more willingly.
We have no knoweledge of how old your
test battery is , what condition it is in or how it has been treated.
NOW if you want a valid
test, it needs to be done apples for apples...start with an alternator that has the same maximum charging voltage as the DC to DC charger.
Do the tests over at least 1 full charge cycle...that means charging for at least 8 hours and resting overnight.
Use batteries of a known condition that have been cycled, equalised and tested so their behaviour is known
AND with the vehicle moving so the engine runs at at least 2500rpm.
Then you have the beginnings of a valid
test.
As it stands, any differences can be put down squarely at terminal voltage.
cheers
FollowupID:
808286
Follow Up By: oldtrack123 - Monday, Feb 10, 2014 at 11:53
Monday, Feb 10, 2014 at 11:53
HI Brian
Your first set of figures are I believe with direct charging ???
If so it would seem to me that you have excessive voltage drop in the cables.
IN the order of 0.5V!!
Of course. that will make a substantial difference in the charge rate!!
Are you using a diode type isolator??
I suggest the redarc went straight to 'Absorption' because it saw the battery had been charged to 14.4V
Any La battery in good condition will very quickly rise from a steady state of 12.7/12.8V to14.5V when even a few amps are put into it
I have seen that many many times with even simple single stage chargers
As you have correctly posted & seen, it is the absorption time that finishes it off to 100%SOC
An alternator non ecu reg does somewhat similar if the drive time is long enough & the voltage is held around 13.8V[ reduced current input]
you have not given your cables or run length
but i would suggest that the voltage input at the Redarc would be interesting
also are those amp readings into the battery or the ALTERNATOR output
OF course if the Redarc input voltage is low the alternator has to put out more amps to obtain the watts input!!
ie if the Redarc ouput is 14v@ 20A = 280W & the input voltage at its input is only 12V, then 280W/12V=23A
That is neglecting losses in the Redarc, not sure of their claimed efficiency but expect no better than 90%
so actual alternator output would be more like 25.55A.
PeterQ
FollowupID:
808287
Follow Up By: Member - LeighW - Monday, Feb 10, 2014 at 12:05
Monday, Feb 10, 2014 at 12:05
" The Redarc DCDC charger does not stay at a constant current until the battery reaches 80% Soc, in fact, it has dropped to roughly half the original current by the time the battery reaches 60% Soc."
So it is actual even slower charging the battery, I went by Redarc specs which say it will maintain 20A or 40A etc to around the 80% SOC point, clearly your chart shows that it can't even supply 40A at a 50%SOC!
I seem to recall someone stating in another thread that it keeps ramping up the voltage to maintain the charge rate which an alternator can't do, seems the Redarc can't either.
FollowupID:
808289
Follow Up By: oldtrack123 - Monday, Feb 10, 2014 at 12:14
Monday, Feb 10, 2014 at 12:14
Hi
Cannot edit but some other points
As far as I am aware ALL the non ecu alternator regs are 3 Stage[Always have been. even the old elctro mechanical types]
AS one would see if they have an ammeter fitted
First stage full alternator out put IF the battery will accept it
2nd stage, reduced voltage,= reduced charge current
3rd stage, rarely seen unless the a Ammeter is reading actual alternator output ,' NO OUTPUT. ' field current reduced to zero to prevent overcharging.
I totally agree ,the newer vehicles with ecu controlled alternator will not satisfactorily charge any battery to 100%
A DC/Dc charger is almost essential unless one is prepared to use a voltage boosting diode in the battery to alternator sense circuit!
PeterQ
FollowupID:
808290
Follow Up By: oldtrack123 - Monday, Feb 10, 2014 at 12:22
Monday, Feb 10, 2014 at 12:22
HI
A correction to my 2nd last post
I see at one stage you actually had a full 1.0 V loss in the cables with direct charging!!
AND that was with only around 14A
THAT to my mind is unacceptable for any purpose on a 12V set up
8% loss with just 14A no wonder the battery did not charge
PeterQ
FollowupID:
808291
Follow Up By: Member - LeighW - Monday, Feb 10, 2014 at 12:29
Monday, Feb 10, 2014 at 12:29
"----------------------11:30-----------13.97---------------------13.40-----------------6.22"
Using Redarcs calculator as you love Redarc:
4 Mters of 6 B&S cable
Cross sectional area = 13.3mm2
Cable temp 25C
Max current 6A
Estimated voltage drop .03V
Don't know what cable you were using but if you were getting .43V something fishing is going on and the validity of your testing is suss to say the least.
FollowupID:
808293
Follow Up By: oldtrack123 - Monday, Feb 10, 2014 at 12:56
Monday, Feb 10, 2014 at 12:56
HI Brian
Your quote"Steve,
First point that I will make is that the Ctek unit is not recommended for use on low alternator voltage vehicles due to its relatively high cut-out point, all other brands seem to be able to handle the lower voltages quite well.
Contrary to what is being said on this thread, DCDC chargers such as the Redarc etc. compensate very well for line losses."
Both statements I agree with particularly the last one
THEY compensates for line losses they do not correct the line losses
Those losses are still there, possibly wasting alternator capacity If the alternator has other loads
.A volt or two is not be critical in low voltage applications , but in 12V systems it causes big problems
I do hope those who use D c /Dc chargers watch how hot those cables feeding the dc /dc charger get !!
They do have to carry MORE than the CHARGER'S output current, anything from 10% to possibly 40% more!
that can be seen from Brian's tests I expect he is using a 20A charger yet the alternator output is much higher
Howeve I would suggest Brian has a high resistance connection somewhre in his system as the voltage drop with 2Mof 6B&S with 10A current flowing should only be around 0.052V =0.37%
FollowupID:
808295
Follow Up By: oldtrack123 - Monday, Feb 10, 2014 at 14:48
Monday, Feb 10, 2014 at 14:48
HI Leigh
Volt drop tables & cals can always be a problem , one needs to be certain as to if they are based on "Run ' Length or ACTUAL length of single cables
Mine was correctly based on run length[perhaps I should have stated that ]while yours is correctly based on actual length of single cables
So Both our answers are RIGHT
Just in case some do not understand
whichever way it goes ,there is something seriously wrong with either Brian's figures or his set up
PeterQ
FollowupID:
808304
Follow Up By: The Bantam - Monday, Feb 10, 2014 at 19:12
Monday, Feb 10, 2014 at 19:12
Remember friends, there are 3 certainties in this life.
DEATH
TAXES
VOLTAGE DROP.
Don't get over obsessed with the voltage drop...there will always be some.
The single biggest issue in this argument is the charging voltage.
And that charging voltage varies much more than the voltage drop.
Increase the charge voltage at any point by a full Volt and the charge rate will increase considerably.
cheers
cheers
FollowupID:
808323
Follow Up By: Brian 01 - Monday, Feb 10, 2014 at 20:56
Monday, Feb 10, 2014 at 20:56
To clarify a few points here, and that will be the last from me as this will just go on ad infinitum.
1. Oldtrack..Surely you jest. Excessive voltage drop with just a 4 metre circuit length of 13mm2 cable, and the cable specs were posted.
No
isolator of any sort was inserted between the batteries on direct charge.
2. Bantam.
To your first point, do you honestly think that the rate of charge to the 2nd battery would have miraculously increased given more time?
To your 2nd point. Of course the increased current can be attributed to the DCDC higher charger voltage, that's the whole point of them.
To your point 2A. If you look closely you will see that both charge times were of one hour duration, and the DCDC test started at a lower voltage but ended up a whole volt higher.
What does that tell you?
To your 3rd point. the vehicle was stationary but engine revs were set at 2000 RPM which is equivalent to about 100kmh. How fast do you drive? And that crap about vehicle motion stirring up the electrolyte, it just keeps getting better.
To your 4th point. Anyone with any real knowledge of battery chemistry would be aware that acid is heavier than water and will therefore gravitate to the bottom of the battery. Specific Gravity readings will always be lower at the top of the cell not the bottom as you state.
The rest of your post is basically rant so I'll leave that alone.
3. LeighW.
To your statement " So it is actual even slower charging the battery"
Did you even read the figures, the DCDC charger is at least 2.5 times
faster.
Do you also believe, as Bantam does, that the charge rate is going to miraculously increase as the battery voltage gets higher.
The charger is obviously ramping up its voltage to maintain the charge rate within its capabilities.
A look at comparative voltage versus charge current for the alternator at time 10:34 shows volts at 14.10 and current at 14.5 and for the DCDC charger at time 3:03 shows volts at 14.10 and current at 34.86, yet you still claim the direct alternator to be better???
With regard to the later posts by Oldtrack and LeighW about presumed excessive voltage drop in the wires, or faulty connections.
I have to assume that you're not both kidding here.
Consider the indisputable fact that the total voltage drop in any circuit is equal to the sum of all of the individual voltage drops in that circuit.
So....'Let's look at the charging circuit route:-
From crank battery negative terminal, through black connecting lead (which will have some resistance and voltage drop across it), through the 2nd battery (which will have high internal resistance and voltage drop across it, decreasing as battery becomes charged), through red connecting lead (again some resistance and voltage drop across it), back to crank battery positive terminal.
Now.. allowing for normal voltage drop in the connecting wires, where do you suppose the rest of your unexplained voltage drop is occurring?
Perhaps you might consider the internal resistances as a prime candidate.
A couple of questions
1. Have either of you ever connected a flat battery to a fully charged one and seen both voltages instantaneously equalise?
2. Have either of you ever connected a charger with a say 14v output voltage to a battery at say 12v, and seen an instantaneous jump in voltage of the flat battery to that 14v?
The answer to both questions would have to be no because it won't happen, so did you put that difference in the two voltages down to just the resistance of the wiring, or poor connections without ever considering the voltage drop across the internal resistance of the battery?
There was no excessive voltage drop or poor connections, the results are entirely in keeping with expected figures.
That's it from me.
FollowupID:
808333
Follow Up By: Member - LeighW - Monday, Feb 10, 2014 at 22:01
Monday, Feb 10, 2014 at 22:01
Brian a simple calculation shows you couldn't possibly obtain the voltage drop you did using the specified cable at the current you have quoted, therefore your measurements leave a lot to be desired or you have fabricated the readings!
FollowupID:
808336
Follow Up By: Member - LeighW - Monday, Feb 10, 2014 at 22:57
Monday, Feb 10, 2014 at 22:57
For those following:
Using Brians own figures:
V1 V2 Vdrop Amps Resistance of cable
14.09 13.09 1V 12.3 .081
14.08 13.3 .78V 10.9 .071
14.04 13.34 .7V 10.1 .069
14.02 13.36 .66V 9.8 .067
13.97 13.35 .62V 8.32 .074
13.97 13.36 .61V 7. .087
13.97 13.4 .57 6.22 .092
It seems in Brians test setup the resistance of the cable changes as the current does!
I would suggest Brian has a serious measurement issue or he has very unique cable!
As a matter of interest if you check out Redarcs calculator it indicates 6B&S will have a resistance of approximately .005 ohms for a 4 meter length, and a calculated voltage drop of .06V for 4 meters of cable carry 12.3 amps, this varies markedly from the 1V drop Brain measured during his testing.
I suggest that Brain goes back and tests properly.
FollowupID:
808339
Follow Up By: oldtrack123 - Monday, Feb 10, 2014 at 23:44
Monday, Feb 10, 2014 at 23:44
HI Brian
I do not jest
You figures show a large voltage difference from one battery to the other with only 2M run of 6B&S cable in between
[quote]Enginerunning..
....10:34........14.10........................12.78...................14.50
-10:35-----------14.09---------------------13.09----------------12.30
{end quote]
1.32Vlost with 14.5Aover a2M run length of 6B&S cable
I'msurprised that an electrical engineer would not immediately suspect something was wrong to have such a voltage loss with that current!!
I have posted & has Leighof the Calculated voltage drop over that length
using the above figs for 14.5A it should only be 0.052V
Perhaps you have some other reason for your readings if so we would be interested?
AS it stands the exercise is worthless IT cannot be used for any comparison purpose
IF those sorts of voltage lossesare accptableto you then no wonder you consider a dc/dc charger essential
PeterQ
FollowupID:
808340
Follow Up By: oldtrack123 - Monday, Feb 10, 2014 at 23:54
Monday, Feb 10, 2014 at 23:54
Hi Brian
By the way we do not need a lecture in circuit resistance, what makes up a circuit etc voltage drop etc
I am not that senile yet
BUT perhaps YOU have not given ALL the detail
YOU SAY the only thing between the TWO batteries is a 2M run length of 6B&S cable!!
The voltage drop in that cable is very easily calculated for any t current flowing. an exercise has been done for both 6A & 14.5A,
can YOU fault THOSE figure??
FollowupID:
808341
Follow Up By: The Bantam - Tuesday, Feb 11, 2014 at 00:00
Tuesday, Feb 11, 2014 at 00:00
Brian mate your experiment is findamentally flawed in so many ways, and your reasoning is likewise fundamentally flawed.
1. don't obsess about the voltage drop.....the first and fundamental flaw of this experiment is that the Dc to DC charger outputs a full Volt more than the alternator.....voltage drop or no voltage drop that is why the dc to dc charger works better in this case.
2.No I am not claiming that the rate of charge mirraculously did anything...but I have seen batteries particularly old ones plenty of times start with a low charge rate and improve over several hours.
For this test to be valid the test battery has to have a proven consistent behaviour, before the test.
As I say if you are comparing a 13.8 volt alternator with a 14.whatever volt DC to DC charger you are not comparing apples with apples...try the test with a 14.something volt alternator and see how you go.
The point of dc to dc chargers is not to increase voltage...you can do that with a $2 fuse diode in most cars.
The purpose is to compensate for voltage drop in cables....which is not the problem here.
As for "acid stratification"
This is a very well documented issue with batteries...yes acid is heavier than water...but it is not that simple and it is well known that SG can be uneven thru the depth of the cell.
The difference in specific gravity is very small, and when there are other influences on the fluid such as heat and rising gass, the heavier acid may remain at the top of the cell resulting in inaccurate and inconsistent readings...THIS is why your SG readings do not agree with your voltage readings.
Unless the acid is agitated my either motion or vigorous gassing, it takes time for the SG to equalise thru the depth of the cell.
Do you also understand that in a wet cell battery, the top part of the plates is more active under charge than the bottom part of the plate...particularly at low charge rates and the early part of the charge cycle..
The reasons are interesting ...but the result is more acid and more heat is generated at the top of the cell.
Result..acid stratification, hotter but heavier and more concentrated acid remains at the top of the cell with cooler and lighter acid and water at the bottom.
None of your figures prove anything appart from your method and conclusions being unreliable.
Seems you know just enough to draw an incorrect conclusion.
cheers
FollowupID:
808342
Follow Up By: The Bantam - Tuesday, Feb 11, 2014 at 00:05
Tuesday, Feb 11, 2014 at 00:05
Oh on the matter of alternator RPM.
Do you have curves for your alternator and or have you tested the output of your alternator.
Have you logged the alternator behaviour into the test batter on its own.
OH are we not forgetting that the alternator is a full volt lower in charging voltage to the DC to DC charger.
Nothing else matters because of this gross error in comparision.
cheers
FollowupID:
808343
Follow Up By: oldtrack123 - Tuesday, Feb 11, 2014 at 00:08
Tuesday, Feb 11, 2014 at 00:08
HI Brian
RE [Quote oute]
So....'Let's look at the charging circuit route:-
From crank battery negative terminal, through black connecting lead (which will have some resistance and voltage drop across it), through the 2nd battery (which will have high internal resistance and voltage drop across it, decreasing as battery becomes charged), through red connecting lead (again some resistance and voltage drop across it), back to crank battery positive terminal.[end quote]
WHAT ALOAD OF HOGWASH
Do you actually think we are 6years olds that we do not know what constitutes an electrical circuit k
How the hell where you measuring those voltages
Surerly with the direct charge setup you were reading voltage at EACH batteries tern minals
or do you have some strange method that normal electrical people do not use??
PeterQ
ps Do not squib out NOW!
FollowupID:
808344
Follow Up By: oldtrack123 - Tuesday, Feb 11, 2014 at 01:42
Tuesday, Feb 11, 2014 at 01:42
HI Brian
As for the rest of that LOOONG post of your'
IT is full of misunderstanding, although it looks good
I must go now but I WILL COME BACK tomorrow LATE to go through THAT
BUT just to confirm, you are an ELECTRICAL engineer ???
Because you do not seem to know where or how to do some simple measurements tr determine voltage drop from one source to it's load
Perhaps that is why you have needed a DC 'DC charge
Still waiting for YOUR explanation as to how you can get such a large voltage difference from one end to the other of such a short heavy cable under a relatively light load current for a
cable rated@ around 80A.???
r
PeterQ
FollowupID:
808349