VSR and MPPT combo vs DCDC charger

Mded55

New Member
Hi,
I currently have a basic dual battery system. It is comprised of a VSR which separates my aux battery which is in a battery box in my Ute tray. I want to add a fixed solar panel to my roof of my canopy and am tossing up between two options. I don’t have a smart alternator.

Option 1 (preferred option, as it is cheaper as I simply have to plug the MPPT into my battery box) :
Connect my solar system to my aux battery via a MPPT controller. My questions about this set up is:

When driving: Will both the alternator and solar panels charge the aux battery? Would the charge produced by the solar panel charge both my aux and starter battery when the relay is open (starter battery is above 13v, and assuming my fridge compressor is off which is the only accessory drawing current from the aux battery whilst I drive)?

Option 2 (not preferred, as I would need to change wiring, but I will do it if it is has significant advantages to option 1)
Get rid of the VSR and install a DCDC charger with a built in MPPT. My questions about this setup is:

When driving: Would the DCDC charger prioritise the charge from the solar system and thus my alternator would not be working as hard ?

When stopped: would the solar system charge both the aux and starter battery ? Does the DCDC charger isolate the starter battery from the aux battery of the starter battery voltage drops to a certain voltage?

I have done some extensive googling but cannot find the information I need to make my decision. Any help/info/guidance would be awesome. Many thanks -Matt
 

red hilux

Well-Known Member
The DCDC option is a better option.
Depending on what type battery you have, they all like to have different charge profiles to optimise it’s charge.
Also depending on where your battery is, volt drop can also reduce optimum battery charging, a dcdc charger next to the battery ( or as close as possible ) is the best option.

While it sounds expensive right now. Spend the money on a good quality unit and do it once


A good quality unit will use what ever it sees fit to best charge. It can/will use both solar and alt while your driving
 

Triton14

Well-Known Member
I cant answer all your questions but if you already have a VSR based system then for ease of install & cost effectiveness I would just be adding a MPPT controller to allow for the solar charging.

I have a similar set up with a redarc dual sensing isolator & a MPPT controller on top of my battery box I made up myself.

Its all about your personal preference.

If you look at the links in my signature you will see my set up.
 
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Lost1?

Well-Known Member
Another yes for the DCDC charger if you don't intend to run a switchable relay to enable both batteries to be engaged for winching or starting the vehicle if the crank battery dies when remote. REDARC and ENERDRIVE make a charger that will prioritise solar over drawing charge from the alternator. I recommend you select a charger that will handle all battery types. You may want to change to Lithium later as this technology becomes cheaper. Do a bit of reading to decide which one has the best specs for charging in extreme heat or cold.
 

cam04

Well-Known Member
If I had an existing system I’d just have a cheap mppt off the panel and be done with it. Panels finish charging AGM’s quite well so the charge profile advantage of a dc charger is minimised. Change the vsr to a 2 way vsr to back charge the start battery off the panel and you have ticked most of your boxes.

starting out new is a different story, same thing if money is no object, but that is rarely the case. Doing it well is not a cheap exercise and you don’t have a smart alt to worry about anyway.
 

Triton14

Well-Known Member
If I had an existing system I’d just have a cheap mppt off the panel and be done with it. Panels finish charging AGM’s quite well so the charge profile advantage of a dc charger is minimised. Change the vsr to a 2 way vsr to back charge the start battery off the panel and you have ticked most of your boxes.

starting out new is a different story, same thing if money is no object, but that is rarely the case. Doing it well is not a cheap exercise and you don’t have a smart alt to worry about anyway.
Exactly what I was implying ;)
Why spend way more money that you need to meet you current objective??

Future proofing = lots of $$$!!!
 
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Mded55

New Member
If I had an existing system I’d just have a cheap mppt off the panel and be done with it. Panels finish charging AGM’s quite well so the charge profile advantage of a dc charger is minimised. Change the vsr to a 2 way vsr to back charge the start battery off the panel and you have ticked most of your boxes.

starting out new is a different story, same thing if money is no object, but that is rarely the case. Doing it well is not a cheap exercise and you don’t have a smart alt to worry about anyway.
Thanks for the info, I wasn’t aware that there was such a thing as a 2 way vsr.
 

Albynsw

Well-Known Member
Do you really need to charge your cranking battery via solar? If not just leave the VSR in that you have and wire the solar panel via a controller to your auxiliary battery
Simples.
 
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Mded55

New Member
Do you really need to charge your cranking battery via solar? If not just leave the VSR in that you have and wire the solar panel via a controller to your auxiliary battery
Simples.
Probably not; the reason why I want to do it is I am running my compressor and my winch from my starter (whilst the vehicle is on).
 

Albynsw

Well-Known Member
Probably not; the reason why I want to do it is I am running my compressor and my winch from my starter (whilst the vehicle is on).

I wouldn’t bother if you are trying to keep it cheap and simple, that is no different to every other vehicle that doesn’t have solar and it isn’t an issue
 

rob_macca67

Well-Known Member
Do you really need to charge your cranking battery via solar? If not just leave the VSR in that you have and wire the solar panel via a controller to your auxiliary battery
Simples.
Once a VSR is Closed from driving, etc, it will remain closed whether the solar is connected to the MAIN or AUX battery. It's not until the VSR lower disconnecting voltage (cut-out) limit is reached that the VSR will disconnect. This is not a bad thing as u are utilising your starter battery capacity as well, thus having a greater capacity. This lower Disconnect voltage "should" be set at a level that will leave enough capacity in your main battery to start your engine.

I've been using this system for years w/o any issue, but I'm also not one to stay in any one place more than a day or 2 or 3 at most... I run the dual sensing VSR as this has some advantages for me when I connect my solar to my rear Anderson plug which comes of the Aux Battery. This way it charges the Aux first, then when it reaches it's "Cut-in" voltage, then starts to charge the Main battery as well. Once the voltage falls below the "Cut-out" voltage, the 2 batteries are disconnected. It's a cheap and effective system when your car is not running these smart Alternators.

I know others will disagree, but it's worked for me for years w/o me having to outlay huge $$ for those expensive Redarc products. I will look at buying a Lithium when I feel the price has come down to a level where I can afford to buy one but I also know then that I will also have to change my charging system as well to match the Lithium operating/charging characteristics...
 

peterfermtech

Well-Known Member
Has this whole "woke" thing got to a point where we have to be sympathetic to alternators in case they work too hard?

When you're driving let the alternator do the work it was designed to and provide plenty of current to your batteries. The DC to DC will probably only take current from the alternator anyhow but will be limited because of the circuitry. When you're stopped let the solar/mppt do the work it was designed to. It generally won't work whilst you're driving because the voltage of your alternator will be above the cutout voltage.
Just invest in a good quality MPPT. As others have said "Easy".
 

Mded55

New Member
Has this whole "woke" thing got to a point where we have to be sympathetic to alternators in case they work too hard?

When you're driving let the alternator do the work it was designed to and provide plenty of current to your batteries. The DC to DC will probably only take current from the alternator anyhow but will be limited because of the circuitry. When you're stopped let the solar/mppt do the work it was designed to. It generally won't work whilst you're driving because the voltage of your alternator will be above the cutout voltage.
Just invest in a good quality MPPT. As others have said "Easy".
Thanks for the input. I don't understand: "It generally won't work whilst you're driving because the voltage of your alternator will be above the cutout voltage". 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? I agree the alternator needs to do what it is designed to do, but I am trying to improve my current system and learn at the same time.
 

peterfermtech

Well-Known Member
Thanks for the input. I don't understand: "It generally won't work whilst you're driving because the voltage of your alternator will be above the cutout voltage". 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? I agree the alternator needs to do what it is designed to do, but I am trying to improve my current system and learn at the same time.
Basically.
The vsr does it's voltage sensing on your starter battery. This means that if the voltage on the starter battery is below a set cut out point the circuit is open (relay contacts open) and current can't flow between batteries. When the starter battery is near full charge and the alternator is running then the voltage will reach a set point that closes the relay and voltage can flow between the batteries. Due to the charging voltage from the alternator the auxiliary battery will soon reach a voltage on the terminals that the circuit on the mppt believes is a fully charged battery and the mppt will stop charging.
 

Batts88

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.
 
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Triton14

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.

I fitted the SBi12D when building my system but after looking around yesterday there are cheaper brands of dual sensing VSR's around-



While some may say its unnessacary I think anything you fit that can have a dual purpose is better than not having it at all, like the override to connect both batteries for winching or aid in starting.

As I mentioned earlier, the way people do their set ups is an individual thing!
 

cam04

Well-Known Member
The main thing with dual sensing IMHO is that the start battery is going to see a complete charge off the solar panel and extend its life. I sold the ranger at 8 years old with the original start battery in it. I put this solely down to the ctec system i have allowing the panel to back charge the start battery - and I had the smart alt turned off.
 

peterfermtech

Well-Known Member
I fitted the SBi12D when building my system but after looking around yesterday there are cheaper brands of dual sensing VSR's around-



While some may say its unnessacary I think anything you fit that can have a dual purpose is better than not having it at all, like the override to connect both batteries for winching or aid in starting.

As I mentioned earlier, the way people do their set ups is an individual thing!
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.
 

Batts88

Well-Known Member
I fitted the SBi12D when building my system but after looking around yesterday there are cheaper brands of dual sensing VSR's around-



While some may say its unnessacary I think anything you fit that can have a dual purpose is better than not having it at all, like the override to connect both batteries for winching or aid in starting.

As I mentioned earlier, the way people do their set ups is an individual thing!
Yeah it's good if you get the correct size for winching as some are just to aid starting the engine. Snatch blocks are also a great aid for winching I would use one long before considering to link batteries.
 
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