DC/DC charger though solar regulator

Sorry, I didn't address your specific questions:

No, you can't connect the DC-DC charger output to the solar reg's solar input and trick it. The DC-DC charger MUST be connected direct to the target battery so it can work out what it has to do.

"i am guessing the only issue is to make sure that the DC charger is less than 20 amps output, would this be correct."

If this question is in relation to connecting the DC-Dc charger to the solar input of the Dingo, then the answer is it's not a relevant consideration. As above, you can't connect them that way.

In other respects there's no direct relationship or restriction about matching output currents of the two devices, they are independent in that regard.

Cheers

Just a couple of points worth considering.
1. For best performance, the DCDC charger should be located as close as possible to the battery that is being charged. In the tug is really not good enough.

2. It has been suggested to use a Ctek 250s dual, but be aware that this device will not work correctly with some of the newer computer controlled alternator cars and won't boost voltages that come into the unit lower than 12.7v, which would likely preclude your high voltage drop situation. Ctek have come up with a partial fix for this, but it involves a relay feeding the alternator into the solar input whilst underway, and will still only work down to 11.5v

3. Both the DCDC charger, whichever brand you choose, and the solar controller, whichever brand you choose, need to see the battery with no other device in between, this is so that they can properly ascertain battery condition in order to select their correct charge parameters.

4. Even with a DCDC charger, you should ensure that your charge cables to the device are large enough to limit voltage drop to acceptable limits. The DCDC charger will, in the process of increasing the output voltage, draw more current at the input which will further exacerbate voltage drop problems.

G'day Brian,

I made the suggestion to use a Ctek as one option. In relation to your point 2 above, thanks for the heads-up re Ctek low voltage limitations. Where did you find that info? I can't see any reference to a low voltage spec in their documentation, which is a bit deficient IMO.

My suggestion to use the Ctek was based on satisfactory use by a number of members in our caravan owners club, but we're all into heavy gauge supply cabling so that may have hidden the Ctek's limitation.

I will bear your caution in mind in the future.

Cheers

From my readings and research on the CTek, it isn't actually an inverter / voltage booster design like the redarc. It's just a charge regulator.

Pat

Hello Frank. I became suspicious of the lack of that same info in their advertised specs some time back and so contacted Bainbridge about it.

I pointed out that they did not list a voltage at which the unit would continue to operate down to and asked what that might be.
They initially told me that it could go down as low as the Redarc device, but when I pressed them for printed data they were unable to produce it. I suspect this was simply lack of product knowledge rather than intended misinformation.
Subsequent discussions with them disclosed that the unit will not charge if the input, either loaded or unloaded, falls below 12.7 volts.
They confirmed that this had caused them some problems with the later computer controlled alternators and with largish voltage drops. Ctek notified me of a partial fix where an added relay will switch the alternator onto the solar input when you are driving and return the solar to that point when stopped. This still only works down to 11.5v, which should be OK for most uses, but it is still far short of other DCDC chargers out there, and does the require the mod.
They have since advised me that they do not recommend its use in cars with computer controlled alternators.

Pat, the ctek 250s dual, whilst not like true DCDC devices, will take an input, provided it is above 12.7v, and boost it to the required voltage to charge your battery.
In that regard, I also don't consider it to be a DCDC charger in the sense that other such devices are .

For your interest, the Redarc BCDC1220 will operate down to 9v, will not turn on until the input reaches 13.2v and will turn off on no load test at 12.7v.
Their LV model, specially designed for newer computer controlled alternators, will turn on at 12v and turn off on no load test at 11.9v.
I have no affiliation with either company.

patsproule posted:
From my readings and research on the CTek, it isn't actually an inverter / voltage booster design like the redarc. It's just a charge regulator.

Pat{'End Quote}'


Hi Pat
One needs to understand electrical terminollogy to get it right]
The Ctek 250DS certainly is not an inverter

An inverter changes DC to Ac

the Cetek is basically a CONVERTER
Iit takes Voltsx Amps[Watts] at some combination & converts that to Volts &Amps of a different values [say13v with 10A input to 14V at around 9A output into charging a battery

But the Ctk does more than that IT ALSO A MULTI STAGE CHARGE REGULATOR

PeterQ

Thanks Brian. Very interesting. That sort of info and limitation should be published. I wonder why they designed it that way.

Cheers

Frank, there were a few models of DC-DC chargers designed that way 8 - 10 years back. In those days there were none of the modern alternators around. The standard alternators with temperature did not drop much below 13.5 V. The drop out voltage was set high enough so that users did not have to install battery isolators or ignition controlled relays.

If you look down near the bottom of the User Manual (page 11 on one and 12 on another) you will see:

ChARGING PROGRAm D250S DUAL
The charger starts charging the target battery when the supply voltage exceeds 13.1V for 5 sec (engine on).
The charger stops charging the target battery when the supply voltage drops below 12.8V for 10 sec (engine off).

All of the true DCDC chargers have similar on/off no load voltages to the ctek
This is for crank battery isolation when the motor is not running.
The difference is that the others can go down to a much lower voltage when the motor IS running in order to be able to allow for voltage drop in the charge circuit or for comp controlled
alternators.

HI Brian
AND what happens to the CRANK battery if you do not have anything like that that voltage drop???
Lets assume the cable voltage drop is only 2V!!
What can the Crank battery then be pulled down to?
Particularly IF the alternator is under heavy load & it's voltage is heavily depressed!!
Again I will say
WHY would ANYONE suggest that cables which give uo to 27% voltage drop under load are OK & best compensated for by such an arrangement
The sensible thing to do is ENCREASE the cable SIZE to reduce the VOLTAGE drop to a MORE accptable level

PeterQ

That's easy Peter.
Take the Redarc BCDC1220 as a common example of true DCDC chargers.
The charger shuts down its charge every 100 seconds to test the unloaded input voltage.
No current equals no voltage drop on the circuit and therefore it gets an accurate indication of prevailing crank battery voltage.
During that test, if the device sees the input voltage as being lower than 12.7v, then it ceases to charge until such time as it sees it increased to at least 13.2v.
Stop the motor, and the charger remains in operation (unless you have used the ignition control function) until such time as the input falls below 12.7v, so the crank battery is fully protected.

Therefore, to answer your question - the lowest that the charger can pull the crank battery down to is 12.7 volts.
Remember that the lower voltage levels that this unit may be working at is not necessarily the same voltage that is present at the crank battery terminals.

If the crank battery falls below that 12.7v or even lower due to overly heavy loading on the alternator, then it is not the fault of the DCDC charger, and you would be advised to seek help in getting it rectified.
I agree that adequate cable sizing is essential but at least these devices can compensate somewhat for any deficiencies in that area, and certainly for variable voltage alternators and in fact for the vagaries of any direct alternator charging method.
With respect to your 27% (9v cut off @20s under load) voltage drop figure which you seem to attributed to me, smarter folk than you or I decided on that number, and it is fairly consistent across a whole group of manufacturers, perhaps you should ask them.

Here we go again, you are posting your misinformation about true and false DC - DC chargers (yes I know you did not use the word false but using the term true means there is also a class of false ones.)

Boosters (or DC - DC chargers as they have lately become known as) have been around for over 25 years that I know of. The early ones required some form of isolator to prevent them from over discharging the starting battery. In the early 90s some manufacturers produced models with a higher voltage cut-off point so that isolators were not necessary. There was no talk of them not being true boosters (or in later terminology DC- DC chargers.)

As technology has progressed we now have alternators whose output voltage is controlled by the engine management systems. The older higher cut-off voltage boosters have sever limitations that make them of little use with these alternators. Does that now render them of little use in their intended application? They are true equipment, they just have limitations precluding their use in modern vehicles.

HI Brian
RE Quote"With respect to your 27% (9v cut off @20s under load) voltage drop figure which you seem to attributed to me, smarter folk than you or I decided on that number, and it is fairly consistent across a whole group of manufacturers, perhaps you should ask them. [end quote]
Sorry,
But I did not intend to make it seem your figures
Just MY simple caculation that if they operate doewn to 9.6V , even with a Computer controlled alternator at 13.2 V ,it is a 27% loss of voltage due to inadequate cables!!

Thanks for THAT info on the the off load sensing of the crank battery, I was not aware of that function .

OF course another point to be considered with limited [only 20A] output is the driving time required charge a low soc high Amphr battery bank
IF such cases are the norm & the alternator is the non engine Com controlled type,iit may be well worthwhile forgetting about a DC DC charger & use Direct charging with heavy cables so the full alternator is available to put as much charge as possible in during the avaiable time

OR get a higher rated DC DC charger
That again could need larger supply cables

ps have you calculate HOW small the cables would need to be to give 3.6V drop over say 5M at 30A[the input curent req] AND the rated current of that cable


PeterQ

Peter Q, even with only 20 amps from a DCDC charger (and as you are aware, there are bigger output ones available), you will get a far better charge for longer than you will from direct alternator charging.

It will present a constant load to the regulator for the entire time that it is in boost mode, whereas direct alt will very soon reduce its output to a trickle as the crank battery reflects charge voltage.
20 amps from a DCDC charger over say 4 hours driving will do better than the total you will get into a second battery from a direct alternator setup over the same time frame.
They also allow proper charging of different battery technologies, and importantly, they also compensate for the different temperatures of the two batteries, the cooler second battery requiring a higher charge voltage than the hot one under the hood, and this can be done with a DCDC charger but is impossible via direct charging.

A direct alternator charge works well for a single or close coupled battery set but it will not put a sustained high current into a remote/second battery with or without enhancements.

These things were developed for the very reason that direct alternator charging is so vague.

I once again state that I agree with you that adequate cable sizes are essential for good performance even with a DCDC charger, but they do allow for larger voltage drops and voltage controlled alternators, some of which can go down to 12.3v and beyond. The Redarc LV series are particularly aimed at this market with a low voltage cutout of 11.9v.
I don't ever seeing them needing to work down to 9v, that's just what they can do, and all I have ever stated.

PeterD, I may be corrected on the exact date, but I think you will find that the Ctek 250s dual only became available in early 2011 as did Redarc, voltage controlled alternators have been around a lot longer than that, Chrysler started the trend in the 70s, GM and Ford followed in the 90s. It's just the degree of control that has evolved.