Vehicle Charging Through Solar Regulator

Submitted: Tuesday, Jun 04, 2013 at 16:42
ThreadID: 102586 Views:3633 Replies:5 FollowUps:5
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Hello Everybody,
Question: Can anyone inform me if I can charge the van batteries while traveling from the vehicle through the solar panel regulator. I have a 120 amp alternator fitted to the vehicle.

Any advise would be much appreciated.

Regards
Allan and Andrea
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Reply By: Member - J&R - Tuesday, Jun 04, 2013 at 19:33

Tuesday, Jun 04, 2013 at 19:33
In the absence of any relevant additional information to assist us to make an informed judgement, the answer is....
Yes
Maybe
No
AnswerID: 512531

Reply By: oldtrack123 - Tuesday, Jun 04, 2013 at 19:39

Tuesday, Jun 04, 2013 at 19:39
HI
No
Not unless you have a very high current solar reg & you could still have problems

Much more sensible to charge the Aux /van batteries direct from the Alternator but with a battery isolator[ VSR] in the charge circuit


PeterQ
AnswerID: 512533

Reply By: KenInPerth - Tuesday, Jun 04, 2013 at 23:45

Tuesday, Jun 04, 2013 at 23:45
Allan

Not having much info I assume you have an MPPT that you run a portable solar panel through to charge the batteries when stationary and you want to run the same MPPT using the input from your alternator while travelling.

Theoretically there should be nothing wrong with this - the MPPT will accept the alternator as a voltage source and limit the current it draws based on the design (spec) of the MPPT. It should be no different to hooking up a fixed or variable voltage power supply to the MPPT controller (as I think Allan B in a recent post said he uses a 13.8V power supply for similar). I am assuming your MPPT is a "lower current" model like 10A or 20A and will not "kill" your alternator.

Another option is to look at something like the Ctek D250S Dual which has an alternator input and a solar input which would allow for a more permanently wired situation.

Ken
AnswerID: 512541

Follow Up By: Member - evaredy - Wednesday, Jun 05, 2013 at 09:50

Wednesday, Jun 05, 2013 at 09:50
The Ctek D250S is not suitable for vehicles with variable voltage regulators.
I just went through this when installing a DC-DC in the tray of my Dmax. I had to go with a Redarc 1240-LV, but the Redarc 1225-LV is also suitable.
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FollowupID: 790966

Reply By: Member - John and Val - Wednesday, Jun 05, 2013 at 14:29

Wednesday, Jun 05, 2013 at 14:29
Allan,

The simple answer is NO !

Why? Your solar regulator is either an MPPT type, or a "PWM" type. An MPPT regulator accepts the higher solar panel voltage and converts it down to meet the battery's requirements. It cannot convert upwards, which you would require to charge your battery from the vehicle. A so-called PWM regulator does not do any voltage conversion so it would not help to run charging current through it from vehicle to battery. There would of course be losses in doing so too.

The more complicated answer -

You could use some MPPT solar controllers (NOT PWM types and not all MPPT types) fed by a voltage doubler driven by the alternator/main battery. The controller would take the higher voltage and convert it back down to what's required. This is messy, complicated and a suitable high current doubler will be hard to source, and not cheap.

The options -

The simplest - The van batteries can be connected by a voltage sensitive relay (VSR) to the vehicle battery when the engine is running. Heavy cabling is required to minimise voltage losses, and though the batteries will never be fully charged, you will get some charge into them. The solar controller can be left connected to the batteries and won't interfere with such charging.

The best - instal a dc-dc charger near the van batteries and feed it via heavy cable from the vehicle battery. (The charger will usually include the VSR.)This will ensure that you fully charge your batteries. There are several dc-dc chargers ( eg Redarc, Ctec) available that also include an MPPT solar controller.

Cheers

John
J and V
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- Albert Einstein

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AnswerID: 512560

Follow Up By: KenInPerth - Thursday, Jun 06, 2013 at 12:15

Thursday, Jun 06, 2013 at 12:15
John

Couple of things in this thread.

1. I am curious about (but not disputing) the problem referred to by evaredy regaring "variable voltage regulators" and why that would upset the Ctek alternator input (evaredy did not elaborate but I assume the Ctek was dropping in and out of charging ??)

2. I can feed as low as about 12V from a power supply into the solar input of the Ctek (which is MPPT as far as I know isn't it ??) and it will cut in and charge the batteries - I have not tested how much current it will take through the solar input (as in it max's at 20A on the alternator input but not sure if same applies to the solar input).

If it is MPPT will it not just derive as much power from the input as it is designed to do within it's designed limits of voltage and current or do I have the wrong theory about MPPT .... accepting also that not all MPPT may operate exactly the same.

Would solar not at times drop as low as 12V due to environmental conditions and the MPPT controller still generate as much as it can from the voltage available ??
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Follow Up By: Member - John and Val - Thursday, Jun 06, 2013 at 20:15

Thursday, Jun 06, 2013 at 20:15
Ken,

Let me say at the outset that I've no personal experience with the Ctek. It's highly regarded and seems a good bit of technology combining a number functions in a very effective way.

1) The variable voltage alternators being fitted to some recent vehicles drop the charging voltage down low when the engine is idling to reduce engine load, hence fuel consumption and emissions. The Ctek D250S is supposed to drop out if the alternator voltage drops below 12.8V for 10 seconds.

2) The Ctek D250S does include an MPPT controller. I'm very surprised that it will provide any charging current with only 12V on the solar input terminals. I doubt that it's a significant current. It may cut in, but unless it somehow cross feeds into the dc-dc charger, the low "solar" voltage (12V) simply isn't high enough to provide any charging. To provide charging that 12V needs to be increased, and that is not the function of most MPPT controllers. I don't have a D250S, so hope someone else may be able to shed some light on this one.

"If it is MPPT will it not just derive as much power from the input as it is designed to do within it's designed limits of voltage and current or do I have the wrong theory about MPPT .... accepting also that not all MPPT may operate exactly the same." Ken, those design limits are unknowns! Generally, an MPPT controller accepts the energy from the panel and loads the panel (ie draws current) sufficient to pull the panel voltage down to a level where the power from the panel (voltage x current) is maximised. (This occurs for most "12V" panels at about 17-18V.) It then converts this voltage and current to suit the battery's requirements. (Typically 14.4V with a corresponding increase in current. It is this ability to trade the excess voltage for extra current that makes MPPT so attractive.) With very rare exceptions, solar controllers will always need to convert the voltage DOWN and consequently lack the ability to convert upwards. Converting up (as a dc-dc charger does) uses similar techniques, but the components are arranged differently. The D250S is an interesting combination - a down converter for solar and an up converter for the alternator, no doubt sharing as much circuitry as possible. Maybe I'm overlooking something. Could someone who has one and has done the measurements please comment - can the box increase a low voltage on the solar input to a charging voltage on the output?

Ken your last question is a good one! The controller will maintain the load on the panel at such a level that the panel operates at the voltage where it delivers maximum power. This means that for most "12V" panels the panel should be delivering current at about 18V. The critical fact is that a solar panel should be thought of as a source of current, not as a source of voltage. Unloaded (zero current) the panel voltage will typically be about 22-24V, whether in full sunlight or moonlight. The current it can deliver though is very different in sunlight from what it is in moonlight! The MPPT controller's first job is to draw sufficient current to load the panel voltage down to the panel's power optimum at about 18V. It's second function is to take this energy and convert it meet the battery's requirements.

Hope that makes sense!

Cheers

John
J and V
"Not everything that can be counted counts, and not everything that counts can be counted."
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Follow Up By: KenInPerth - Thursday, Jun 06, 2013 at 23:42

Thursday, Jun 06, 2013 at 23:42
Thanks John - good info and explanation - I know it digresses a bit from the original query but these things get me curious, and finding much info on design and operation of various makes and models can be hard to find.

I guess an MPPT controller is primarily designed for solar and mulling this over in my mind after I posted it I started to consider that yes the solar panel is pretty much a constant current source over a range of voltage until it hits it's "knee point" around 17 - 18 V and also that lack of sun only reduces current output and not voltage. So until there was no current available, the MPPT would always be operating at around the 17V to 18V at it's input with whatever current was available in the conditions.

As you say, putting any other kind of supply on the solar input and what happens as a result woudl purely be up to whatever the particular MPPT design let it do. I hve been digging around for some circuit diagrams for MPPT and have seen some that are simply a variable regulator that would never work with less voltage in than you want out.

One day I might be able to get around to experimenting more with the Ctek to satisfy my curiosity about how it does actually behave under those conditions. I won't swear to it, but I am pretty sure a quick check I did once on the D250S showed the output to battery at a higher voltage to what I had on the solar input, which would tend to indicate it is actually doing a DC-DC conversion on the solar input. But I need to do some more serious testing before I can claim that.





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FollowupID: 791146

Follow Up By: Member - Munji - Friday, Jun 07, 2013 at 14:37

Friday, Jun 07, 2013 at 14:37
If you want to know more about the Ctec D250S may I suggest you give Battery +Business - Warriewood NSW a call. They were referred to me so I went in there last week and their service and knowledge on this stuff was the best I've experienced so far. 02 9970 6999
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FollowupID: 791196

Reply By: oldtrack123 - Thursday, Jun 06, 2013 at 14:43

Thursday, Jun 06, 2013 at 14:43
Hi Ken

Re"Would solar not at times drop as low as 12V due to environmental conditions and the MPPT controller still generate as much as it can from the voltage available ??""

That very much depends on the MPPT controller design.!
Most available do not have a boost function .
The input voltage must be abobe the battery /load voltage

However I do know of one on the market with a boost function made by Sterling of England, they do have an AUS reseller.

PeterQ
AnswerID: 512641

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