VSR and MPPT combo vs DCDC charger

Triton14

Well-Known Member
I would strongly advise against using an override for winching. The relay contacts are not made for the continuous current that heavy winching can require especially if the starter is depleted. By all means use it between pulls to top up the starter if required however I would suggest just leaving it for emergency starting.
 

CTL

Well-Known Member
I had my wife's car set up the same as your first option for over a yr charging an 85ah agm with a 50w solar panel it works fine. As you said cheapest and simplest option don't get to concerned about the solar being hooked up while the car is running it will sort things out.

Before I added the solar panel the battery volts got to around 12.9v at rest and after fitting the solar it increased to around 13.0- 13.1v so the battery gets fully charged now which may help improve it's life span as the alternator by itself never fully charges it.

If you think for some reason you need the solar feeding the starter battery when the engine is off you'll need to replace the vsr with something like a Redarc SBI12D dual sensing battery isolator but that's more money and if you have no real use for it save your cash and just keep what you have.
Being pedantic now but 12.7/12.8 volts (depends which battery manufacturer’s specs you are using) is fully charged for an AGM battery. Anything over 12.7/12.8 is a surface charge.
 

peterfermtech

Well-Known Member
Lets see!
A winch that could draw up to 500A.
Auxiliary battery wiring that is probably set up for 100 - 150 A (maybe only 50A if you have the small DC-DC unit)
Auxiliary battery fuses set around 50 - 100 A
VSR with 100 A rating

I notice that the diagram does not give any specifications for cable or fuses. I wonder why.
 

Triton14

Well-Known Member
Lets see!
A winch that could draw up to 500A.
Auxiliary battery wiring that is probably set up for 100 - 150 A (maybe only 50A if you have the small DC-DC unit)
Auxiliary battery fuses set around 50 - 100 A
VSR with 100 A rating

I notice that the diagram does not give any specifications for cable or fuses. I wonder why.
Sounds like you know more than the experts Pete & more than the people who manufacture the gear?

Its a hard thing to claim your right 100% of the time which all your recent posts seem to be alluding to.
 

Petunia

Well-Known Member
SBI 12D ...... D denotes ''Dual Sensing'' ... [ I even had the salesman scrambling for the instructions when I informed him I wanted a " D " model ]

now ... we split hairs

The ''Ultimate Dual'' wiring diagram shows a part number '' SBI 212 '' ... yes as a BCDC is used the " D " becomes irrelevant !
12D = 100Amp rating
212 = 200Amp rating [+ 50% tax]
Stands to reason a 200amp solenoid will be more ultimate than a 100, no? as a winch may or may not draw more than 100amp, no?

I won't say the product is bad, it after all is exactly the same [ continuous duty ] solenoid available anywhere, where the product differs is in the '' Brain Box ''.
That brain box will measure the voltage across the terminals of the solenoid amongst other things, if this voltage varies from one side to the other by one half a volt the solenoid will open to protect itself. It is fairly easy to determine that by sound alone, a solenoid opening and closing = sound.

The LED in the unit flashes fault codes, [ one? ] two, and three, I would advise anyone to write them down!

When a solenoid opens and closes with high draw current the terminals will arc, and hence burn/pit/degrade slightly, the lower the rating of the terminal and the higher the current the more degradation at open and closing. Really great solenoids are silver plated/coated, all of my remanufactured ones are also coated in 15% silver or better.

Here Endeth Todays Lesson,
Amen.
:cool:
 

peterfermtech

Well-Known Member
Once you hit that override switch then it's locked and loaded. No voltage sensing. The relay is doing nothing more than being a conductor in the wiring loom. You have connected 2 batteries and any load (winch) with whatever size cable you have running between them. The wiring diagram from Redarc for the "Ultimate dual battery setup for winching" doesn't state cabling size however the wiring diagram for the BCDC1240 states a minimum of 6mm2. What size cable do you think the average Joe Blow will use? Tycab rates 6mm2 cable at 48 A. With derating in a car it is probably closer to 30A. Redarc's protection for that is a 50A fuse.

My point is the override cable's current rating should match the load. For winching say a minimum of 2 B&S. Most won't have that size cable on their dual battery system. The alternator is probably a much better choice.
 

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Petunia

Well-Known Member
Once you hit that override switch then it's locked and loaded. No voltage sensing. The relay is doing nothing more than being a conductor in the wiring loom. You have connected 2 batteries and any load (winch) with whatever size cable you have running between them.
I'm not sticking up for either of you, nor going to say either of you are incorrect?

Apples and Oranges

now ... the quoted statement is correct !
The wiring diagram from Redarc for the "Ultimate dual battery setup for winching" doesn't state cabling size
again correct !
however the wiring diagram for the BCDC1240 states a minimum of 6mm2.
again correct ! BUT!!!!! the

REDARC BCDC1240 and SBI under bonnet wiring guide states 6mm2​

The wiring guide is for 3 batteries on linked under bonnet and one BCDC charged plus all the wobbygongs that go with it, NO winch, AND no Starter override !!

Therefore hence Irrelevant !! AND I see 6mm as adequate for a charge only circuit as shown in that particular diagram !!
My point is the override cable's current rating should match the load. For winching say a minimum of 2 B&S. Most won't have that size cable on their dual battery system.
Again correct, in my opinion, and yes i DO have that in my dual set up, with 900CCA coming up its bottom !!

Apples and Oranges, you can't just take a charging circuit diagram and assume every noddy will use 6mm in a winching diagram, even if I think they will too!!

both arguments here need be on the same page, and both are incorrect with the tangents both going in different directions !!

Amen ! :cool:
 

Batts88

Well-Known Member
Being pedantic now but 12.7/12.8 volts (depends which battery manufacturer’s specs you are using) is fully charged for an AGM battery. Anything over 12.7/12.8 is a surface charge.
For a few yrs now I've found it strange how that surface charge thing works I have quite often run my cdf11 overnight and found the inline digital voltmeter to be reading 12.9v in the morning.
 

Bru9

Active Member
Q1:
Yes, they both will but it will unideal and have problems.
Q2: yes and no, it will be producing peanuts. Define charge? Put in some current? Then yes. Get the batts up from a hungry state? No. Top them up if they are already near full? No coz the time to charge usually is very long and solar is usually poor.
Q3: some do some dont, but most setups have small batteries and they are quite current limited, along with high speed driving with good air flow so the alternator usually handles it fine, you hear stories of alts dieing from ordinary suburban use.
Q4: same answer as q2.
Q5: dc dc chargers dont isolate as they are simply a load like lights or fan etc. But they turn off n on when the alt is running.
I was under the impression that if the voltage of my aux battery is at a certain point (say high 13V) due to solar panel charge, and my starter battery is lower than this, and the relay opens (low 13 V), the start battery would receive charge from the solar panel?
To understand here are the basics.
Current flows from high voltage to low voltage always. Example is you put 2 batts in parrelle (1half full, other full), with most lead acids there will be a moderate flow of current from the full to half full until they both even out.

The bigger the diff in voltage the more current flows. Eg. Hook a 6v light bulb to a 12v battery and boof. The high voltage pushed alot of current into the bulb.
Voltage and resistance can achieve the same thing. Eg a 12v bulb will be dim on a 6v battery, to get more light ( analogous to faster charge speed) you can either increase voltage to 12v, or simply lower the loads resistance ie put a 6v bulb in.
Likewise hook 2 lifepo4s in parrelle and alot of current flows coz they have such low ir.

Current only flows in one direction at a time. Eg a solar panel and fridge hooked to a batt, the panel provides 45w, the fridge consumes 50w, so the batt must supply roughly 5w.

When you hook a batt to power sources ( panels,chargers etc) to each other in parrelle they all atain the same voltage, even two solar panels by themselves eg. Hook a 18v solar panel to a hungry 12v battery, the battery pulls down the PV, and the pv pulls the battery up, so the voltage will be something like 13ish volts (WHY 13 AND NOT 17??? SEE CC/CV). Other factors at play. This means when alt is running the starter terminals can be 14v even if the batt is quite low and mask a sick batt, see cc/CV.

Two batts or cells or panels in parrelle must have identical voltage characteristics, the one with the lowest voltage will limit the lot.
When 3 stage (cc/cv) chargers (dcdc mppt ac etc) are put in parrelle even if they are identical models and set points are identical, they will work well most times in the constant current/bulk stage when batt is hungry, both contributing all their current. But they will fight each other in constant voltage absorption stage and one will drop out and the other will do the remaining heavy work. No two units are ever exactly the same voltage wise, if the unit that dropped out has a end amps style absorb timer it simply goes into float and contributes even less due to its low CV voltage. victron now have some of their chargers synced perfectly by talking to each other.

BATTERY CHARGE ACCEPTANCE RATE
this means how much current can a battery suck at a given applied voltage (absorb set point to be precise) at a given state of charge.
Eg. 14v 100A alt with 100ah Lifepo4 at 50% will most likely pull near and over 100amps for some time.
General rule is all flooded and most agm will only try and suck modest amounts when low and quickly limit current. Bigger batt=more sucking. Ever wondered why you pay $900 for a lifeline agm? Coz they are high CAR batteries and make most look like crap.

BATTERIES HAVE A MAX SAFE CHARGE RATE
Pump too much current into them and they can damage, warp, catch fire. So the safe limit is always less than the max rate it can take. As a rough rule the safe limits are much more important in the upper state of charge/ absorption phase.

Lead acid need a min of ~13.8v for any decent charge time. 14.4 is optimal, lifepo4 ~13.7 min 14v is good buff.

The CC/CV
You dont always charge batteries at a voltage, you charge them to a voltage, when you hook up a high CAR batt to a 14v alt, something strange will happen, its voltage will roll back if it does that is cc. In order for a 14.4v alt to to maintain that voltage, its capacity must exceed the high CAR batts max "pull rate". Simply physics.
Once it rises up and can maintain 14v its CV. Other factors st play like temp, ecu, driving lights.
Absorption/current limiting stage means nothing more than the state of charge % at which the batt is no longer trying to pull more current than the chargers max allows, at the chargers voltage. The cc/CV is define hard in 3 stage charging with standardized absorb set points, but alt charging is more loosely defined.

So running the mppt and VSR at same time is bad, coz the last thing you want is the massive alt to loose out somewhat to that dinky panel. Lol
You can change it's set points to match the alt but...
You can cap both absorb and float to 13.8v and see if that's a good compromise.
Other issue is some like victron mppt wont start unless the PV is 5v plus the batt voltage, that's bad.
Really the panel should only be used once the taper current of the batt is soo low it matches the pv's output. But by then the sun will most likely be gone.

Finally a dc dc chargers main purpose was simply to boost voltage on long cable runs, even .5v drop can murder charge times. They are simply glorified switches that transfer energy from battery to battery. Their advantage of giving the battery a better longer life is not clear cut, as soo many buy cheap batteries and barely use them.

I dont do any witching but if I did, one powerhouse battery is imo going to be better than two mediocre, not to mention the volt drop in those contraptions.
 

rob_macca67

Well-Known Member
So running the mppt and VSR at same time is bad, coz the last thing you want is the massive alt to loose out somewhat to that dinky panel. Lol

Finally a dc dc chargers main purpose was simply to boost voltage on long cable runs, even .5v drop can murder charge times. They are simply glorified switches that transfer energy from battery to battery. Their advantage of giving the battery a better longer life is not clear cut, as soo many buy cheap batteries and barely use them.
Just a couple questions for a dumby like myself...

To help me understand... what is the meaning of cc/CV?

Also, if u had your permanently mount solar panels(mppt) wired up in such a manner that when the engine was running, the solar/mppt was switched out (isolated) from the batteries and when the engine was turned off, the solar/mppt connected and took over (if that makes sense)

Is this a better option instead of having the Car's ALT and Solar/mppt running in Parallel??

I had always thought the DC/DC chargers were for that very thing to cater for long runs of cables, but somewhere along the line they now come across as a "Must Have" item...
Again, I may be wrong here... but the Lithium batteries usually have a inbuilt BSM that governs charging/discharging rates, so I would have thought that as long as your car's ALT puts out the correct Volts, that u don't really need a DC/DC charger, just a Isolator that is driven from the Ignition of the Car... (Car running - Isolator Closed // Car not running - Isolator Open)

Can it be that simple if cable distance is not an issue?

btw: great read (even though it was a bit over my head... lol)
 

Decca

Active Member
cc/cv is Constant currant / constant voltage. Some power supplies can change mode as batteries charge up.
Usually start of charge when load is high it will be constant currant .. or else you might overload charging circuit. then as load decreases it will be constant voltage to finish charge.
Battery System managers (BSM) will control charging of the battery in that it will monitor each cell and charge accordingly. It will also prevent the battery overdischarging.
They don't, to my knowledge, boost incoming voltage.

Re the OP's question... I have a dual input charger (from Jaycar) feeding my Lithium battery. That's it. no VSRs needed as Charger isolates from car when alternater is not running.
I believe mine also tops up car battery.. IF the Aux battery is full AND charger is getting power from the solar panel.. I know the Ctek one that 4WD Supercentre sells does.
Hopefully I've addressed the OPs question as is well past my bedtime..
 

rob_macca67

Well-Known Member
cc/cv is Constant currant / constant voltage. Some power supplies can change mode as batteries charge up.
Usually start of charge when load is high it will be constant currant .. or else you might overload charging circuit. then as load decreases it will be constant voltage to finish charge.
Battery System managers (BSM) will control charging of the battery in that it will monitor each cell and charge accordingly. It will also prevent the battery overdischarging.
Thanks for the info but your statement I highlighted above - I'm not sure that is correct as there is no way the BSM can monitor "each individual cell" within a Lithium. I do believe it will monitor & limit (if req'd) the volts/current as stated in most specs... but happy to be corrected ;)
 

Decca

Active Member
Hi Rob
BSMs that I've worked with have sense wires attached at each connection between cells in a battery.
These wires go to the BSM, as do the Power In and Out wires, and a common wire
Exactly what these sense wires do is up to the electronics, but some BSMs (maybe all?) do resister bleeding, which implies it will load some cells so as charge is even over the battery cells
What happens in a large Lithium Auxiliary battery I presume is similar... and I'm also happy to be corrected.

You have given me some homework to do :)
 
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