Charging System Question

[rupertbear]

If you have an engine driven alternator plus an alternator controller to charge your batteries, how would you then connect solar power to the system?

[b0atman]

Solar controller wires to battery +ve & -ve with an inline fuse .

[WotEver]

As Boatman states, they just connect straight to the battery. The charge controller and alternator will sort themselves out, you don't need to worry about it.

 

Tony

[rupertbear]

Thanks for the replies but could you explain a little further?

 

We go to great trouble so that the voltage applied to the batteries varies according to the state of charge, with either an internal or external regulator. If we then parallel this with a second power source, set to some arbitrary voltage, surely then all this effort is wasted?

 

My study of electrics is now too far in the past to let me work out what happens in the two cases where the solar system output voltage is either set to a little less than the alternator output voltage or a to a little more. Can anyone help?

[WotEver]

Why would the voltage of the 2nd source (solar) be an arbitrary value? Solar charge controllers work in exactly the same manner as a dedicated marine mains charger or indeed an alternator.

 

In the initial stages of charging the charge voltage will be limited by the output power of the device. Once the battery gets out of bulk and into absorption then one or other device will probably take over. It really doesn't matter which, as long as the voltages are correctly set for your battery type.

 

Tony

[DaveGood]

I have a 1kw solar panel connected to the batteries through mppt controllers and inline fuses.

 

Set the system up myself only three weeks ago so performance may differ in the summer but so far the system, due in part to not enough supplying enough power secondly, due to software settings in the mppt controller that I can't alter, and thirdly, because the mppt controller when supplying power reads the battery about 0.3 volts higher then it is, has not now, and probably won't ever damage, the batteries with an overcharge.

 

In my case the solar set up will drop to trickle charge before batteries are fully charged but running the engine will over ride that and complete the charge.

 

DaveGood

 

DaveGood

[by'eck]

If you have an engine driven alternator plus an alternator controller to charge your batteries, how would you then connect solar power to the system?

 

I understand your concerns, but the load discharged batteries present to the two charge sources will likely hold them both below their regulated voltages. They will therefore pull together putting charge current in until the battery voltage rises to the point that one or other begins to regulate.

A larger proportion of the available charge current will then come from the other source. If this is the higher current source, likely the alternator in this case, the solar controller will just idle. This will have little impact on charge time since batteries will be tending toward full charge. In any case it will certainly do no harm to the idling charge source.

[Paul C]

If you have an engine driven alternator plus an alternator controller to charge your batteries, how would you then connect solar power to the system?

 

I read beyond the simple issue of "how do you connect it --> attach wires to the battery" and wondered whether one could intelligently use the aftermarket alternator regulator/controller to "turn down" the alternator's charge current (indirectly - by altering its voltage) and thus the solar controller would take a greater percentage share of the charging. The clever bit is that while it would be lovely to have an automatic way of combining the two chargers to do it at "least cost", one could take manual control and turn down the alternator controller even in situations such as: knowing the weather will improve (ie rainy morning but weather forecast gives sunny afternoon); or knowing there won't be much loads on the electrics in the near future (going to the pub that night instead of staying in with lights on, watching telly), etc and leaning on the capacity of the bank a little, to further save fuel.

[by'eck]

 

I read beyond the simple issue of "how do you connect it --> attach wires to the battery" and wondered whether one could intelligently use the aftermarket alternator regulator/controller to "turn down" the alternator's charge current (indirectly - by altering its voltage) and thus the solar controller would take a greater percentage share of the charging. The clever bit is that while it would be lovely to have an automatic way of combining the two chargers to do it at "least cost", one could take manual control and turn down the alternator controller even in situations such as: knowing the weather will improve (ie rainy morning but weather forecast gives sunny afternoon); or knowing there won't be much loads on the electrics in the near future (going to the pub that night instead of staying in with lights on, watching telly), etc and leaning on the capacity of the bank a little, to further save fuel.

 

Wouldn't it be better to have the engine alternator set to the higher regulating voltage. Better use could be made of engine driven source then. Setting it lower as you suggest so better use is made of the free solar source seems pointless whilst you have the engine running anyway.

[Paul C]

Fuel saving?

[Detling]

Fuel saving?

The best use of solar is to run the engine in the early morning to to the bulk charge at high amps and then let the solar finish the charge off. Most solar set ups cannot provide 50+ amps as can the alternator but when the batteries will only accept 10 amps or so let the sun do its work, as running the engine to charge at this current is very inefficient, you thus save your expensive fuel then.

[by'eck]

Fuel saving?

 

The only way there will be a fuel saving is by loading the engine as much as possible, in this case by increasing regulated voltage over that of solar controller, so max current is put into batteries from alternator in shortest time. Your suggestion would have the engine running longer - I don't see how that saves fuel. You could of course not run engine at all

[Paul C]

 

The only way there will be a fuel saving is by loading the engine as much as possible, in this case by increasing regulated voltage over that of solar controller, so max current is put into batteries from alternator in shortest time. Your suggestion would have the engine running longer - I don't see how that saves fuel. You could of course not run engine at all

 

You're assuming you run the engine to charge the batteries.

 

I'm assuming you run the engine to cruise on the boat somewhere......

[rupertbear]

Why would the voltage of the 2nd source (solar) be an arbitrary value? Solar charge controllers work in exactly the same manner as a dedicated marine mains charger or indeed an alternator.

 

Ah! This I didn't know. Thanks. I had assumed that they simply had a 'dumb' but manually adjustable output.

 

This forum is full of useful information and I have learned a great deal. It can, though, be a bit of a jigsaw puzzle, working from thread to thread to build up a full picture. In this case I must have dropped a piece.

 

If you were starting from scratch, then, could you do away with the dedicated alternator controller and just have the alternator output going into the MPPT with the solar?

[Sir Nibble]

No.

[nicknorman]

Ah! This I didn't know. Thanks. I had assumed that they simply had a 'dumb' but manually adjustable output.

 

This forum is full of useful information and I have learned a great deal. It can, though, be a bit of a jigsaw puzzle, working from thread to thread to build up a full picture. In this case I must have dropped a piece.

 

If you were starting from scratch, then, could you do away with the dedicated alternator controller and just have the alternator output going into the MPPT with the solar?

No, the nature of the MPPT controller is that it expects the characteristics of a solar panel, which are quite different from an alternator. However you may not need a seperate alternator controller. Alternators have built in regulators which are quite adequate for normal needs, only exception being an ancient alternator that regulates at a low voltage.

[Sir Nibble]

http://www.canalworld.net/forums/index.php?showtopic=71234&p=1428643

[WotEver]

http://www.canalworld.net/forums/index.php?showtopic=71234&p=1428643

Nice one, Snib

[dmr]

No, the nature of the MPPT controller is that it expects the characteristics of a solar panel, which are quite different from an alternator. However you may not need a seperate alternator controller. Alternators have built in regulators which are quite adequate for normal needs, only exception being an ancient alternator that regulates at a low voltage.

 

Not sure that I fully agree with you here Nick.

It will obviously depend on the exact alternator voltage and quality of wiring (volt drops) but in general a leisure boat doing long cruising days and short evenings will most likely be fine as long as the voltage is about right. For a liveaboard using the the engine to charge the batteries in winter its different and every last tenth of a volt matters. My own experience is that the soft nature of the typical voltage regulator can also significantly reduce charging performance. The target is to get as many amp hours into the batteries in the shortest time and external controllers are good at this.

 

..............Dave

[nicknorman]

Not sure that I fully agree with you here Nick.

It will obviously depend on the exact alternator voltage and quality of wiring (volt drops) but in general a leisure boat doing long cruising days and short evenings will most likely be fine as long as the voltage is about right. For a liveaboard using the the engine to charge the batteries in winter its different and every last tenth of a volt matters. My own experience is that the soft nature of the typical voltage regulator can also significantly reduce charging performance. The target is to get as many amp hours into the batteries in the shortest time and external controllers are good at this.

 

..............Dave

Yes ok I can go along with that. External alternator regulators probably do help to shorten the charge time a bit. It would be interesting to be able to quantify that. Also depends on the alternator's output - our 175A alternator doesn't drop below 70A until over 80% SoC whereas I suspect if we had a 70A alternator, it would have dropped below max output a good bit before then.

 

So alternator regulator = no change to bulk charging when the alternator is at max output anyway, no difference to the last bit which just takes time regardless. But the bit in the middle where the output has fallen below max - yes, there will be some time saved but how much?

[Sir Nibble]

It will make some difference to bulk charging in that it will extend it. An extra half a volt can take a fair while to achieve.