Battle of the chargers

[mikegunn]

To all electrical experts, and others.

When away from shore power and during daylight my sailboat’s batteries can receive a charge from two sources.

(1) Solar panels which charge at a rate determined by an algorithm in a sophisticated MPPT controller.

(2) When under power, the engine’s alternator which relies on an unsophisticated internal regulator to determine its charging current.

My question is;
If both sources of a charge are active and the MPPT controller applies a voltage that is higher than the alternator’s output voltage, could the alternator’s regulator be fooled into thinking that the battery is full? Resulting in the alternator significantly reducing its output even though the batteries are still hungry.

Mike

 

[Mark26]

 

[PaulRainbow]

To all electrical experts, and others.

When away from shore power and during daylight my sailboat’s batteries can receive a charge from two sources.

(1) Solar panels which charge at a rate determined by an algorithm in a sophisticated MPPT controller.

(2) When under power, the engine’s alternator which relies on an unsophisticated internal regulator to determine its charging current.

My question is;
If both sources of a charge are active and the MPPT controller applies a voltage that is higher than the alternator’s output voltage, could the alternator’s regulator be fooled into thinking that the battery is full? Resulting in the alternator significantly reducing its output even though the batteries are still hungry.

Mike

Yes, this can happen. It can also happen if you connect to shore power whilst the Sun is out, either the solar controller will shut down, or the mains charger will. There is no hard and fast rule though, a lot seems to depend on the actual equipment.

 

[PaulRainbow]

That video is a load of nonsense.

 

[Pete7]

That video is a load of nonsense.

In that case please don't watch the rest of his videos, its just too depressing.

 

[PaulRainbow]

In that case please don't watch the rest of his videos, its just too depressing.

So, you think the video above is not a load of nonsense ?

 

[noelex]

Multiple charge sources are usually not a problem. There can be occasional conflicts, but these are usually very minor.

The alternator will deliver a low output if the solar output is sufficient to keep the battery at the appropriate voltage, and this is slightly higher than the alternator’s setting, but this will charge the batteries correctly .

 

[vas]

didn't manage more than 3mins, but does he claim that if batteries are fully charged (say solar) alternator STOPS outputting even the pulse that runs the tachometer? I'll pass!

 

[Mark26]

Having watched it again, I assume he’s talking about either a modern smart alternator, not the dumb ones most of us have, or one fitted with an external regulator which converts a dumb alternator to a smart one.

 

[mikegunn]

That video is a load of nonsense.

I agree Paul. My problem was not whether or not the engine’s tachometer was working, which it was, because all it has to do is sense a slight voltage pulse. Rather it was whether or not the charging sources would be dominated by the source exhibiting the highest voltage.
Mike

 

[mikegunn]

I

Multiple charge sources are usually not a problem. There can be occasional conflicts, but these are usually very minor.

The alternator will deliver a low output if the solar output is sufficient to keep the battery at the appropriate voltage, and this is slightly higher than the alternator’s setting, but this will charge the batteries correctly .

I agree, but it would take a lot longer to charge at, say 8 Amps from the solar than the 85 Amps potentially from the alternator,
Mike

 

[PaulRainbow]

Having watched it again, I assume he’s talking about either a modern smart alternator, not the dumb ones most of us have, or one fitted with an external regulator which converts a dumb alternator to a smart one.

Can you explain how the alternator stops turning when the solar controller has charged the batteries, because that's what he said.

 

[PaulRainbow]

didn't manage more than 3mins, but does he claim that if batteries are fully charged (say solar) alternator STOPS outputting even the pulse that runs the tachometer? I'll pass!

He claimed the alternator stopped turning.

 

[PaulRainbow]

I agree Paul. My problem was not whether or not the engine’s tachometer was working, which it was, because all it has to do is sense a slight voltage pulse. Rather it was whether or not the charging sources would be dominated by the source exhibiting the highest voltage.
Mike

I had a Sterling mains charger until recently, if i turned it on the Victron solar controller output was virtually nil. I just changed the mains charger to a Victron one and the solar controller keeps charging, whilst the mains charger quickly went into standby. Early days for the new combination, but i'll keep monitoring.

So, It's hard to say for sure what would happen in your case. A decent battery monitor should help to see what's going on. Should you find that the alternator output is severely limited by the voltage from the solar controller you could look into ways to prevent that. For instance, a normally closed relay in the circuit from the solar panels to the controller, with the energising coil connected to the ign switch. I do suspect that you won't need to though.

 

[boatiebert]

Battle of the chargers

I think you missed a good pun ... how about changing the title to, "The Chargers of the Light Brick Aid"?

I have nothing more useful to add.

 

[mikegunn]

I had a Sterling mains charger until recently, if i turned it on the Victron solar controller output was virtually nil. I just changed the mains charger to a Victron one and the solar controller keeps charging, whilst the mains charger quickly went into standby. Early days for the new combination, but i'll keep monitoring.

So, It's hard to say for sure what would happen in your case. A decent battery monitor should help to see what's going on. Should you find that the alternator output is severely limited by the voltage from the solar controller you could look into ways to prevent that. For instance, a normally closed relay in the circuit from the solar panels to the controller, with the energising coil connected to the ign switch. I do suspect that you won't need to though.

Thanks for your very constructive comments Paul. You have al least confirmed my suspicions. Indeed, my next step is to arrange a simple means of isolating the solar whilst under engine and see if the alternator ups it’s game. Most of my sailing is solo, which means I don’t have much opportunity to fiddle down below with disconnects. I’ll report back after a bit more research.
Mike

 

[vas]

fwiw, with a Sterling advanced whatever regulator wired to the stock 60A alternator on my port engine that does a trojan service bank and a victron MPPT and 600W solar on the same bank, I've managed a couple of times to be in such a situation. Having a Venus OS running raspberry monitoring all in and out via a BMV700 shunt it was easy to follow what was going on from the helm seat: batteries not fully charged, starting the engines to go somewhere at 1200rpm (which should produce >20A charge @24V) I had Sterling pumping circa 3A and solar another 15A (consumption being around 4-5A) and all that keeping V at over 27V. OK, sort of normal, would be happier if Sterling would do a bit more work so that batteries would be fully charged sooner (were at circa 80% at the time).
Starting the circa 2kW watermaker (via a Victron multiplus 3K inverter) started depleting bank at a rate that one would expect the Sterling would "wake up" and start sending 20+A.
But no, since battery V was still around 26V (sorry didn't jot down #) Sterling was in fast asleep mode Strangely it remained there even when bank V dropped to 24V (maybe a setting I have to alter on the Sterling, haven't checked tbh)
IMO only solution would be to stop the lot (engine watermaker solar), start watermaker which would drag V low rather quickly (takes circa 90A@25V) and then start the engine which would sense low battery state and start pumping as much as it can. Then I could restart the MPPT to "help" a bit. TBH, all too complicated, might as well fire up the generator and do the lot, only need w/m on for an hour every few days to make up for the loss of water (100lph)
sorry all values a bit approx but you get the idea.

cheers

V.

 

[vas]

He claimed the alternator stopped turning.

lol, yes heard that, I hope he actually meant stopped producing any Amps, however an excited alternator that starts sending pulses (W terminal or whatever you call it) surely cannot "loose" that status and stop sending pulses for the tachometer, can it?

 

[Mark26]

Can you explain how the alternator stops turning when the solar controller has charged the batteries, because that's what he said.

Yes, he did indeed say that. I can only guess it was a slip of the tongue. The most helpful part of the message was that it’s perfectly ok to have two charging devices working at once.

If our object is to charge the battery, that will be achieved satisfactory, it matters not which device is doing the work.

The OP is concerned that the alternator may reduce its output if the solar charger is running. The alternators internal regulator does not control the charge current, that is dependant on the draw, the regulator controls the voltage. The main concern should be not to exceed the max safe charging rate of the battery.

 

[noelex]

I agree, but it would take a lot longer to charge at, say 8 Amps from the solar than the 85 Amps potentially from the alternator,
Mike

If the solar controller is programmed correctly it will try to deliver the maximum current the batteries can safely absorb. If there is insufficient solar power to achieve this, the voltage will be below the target voltage and the alternator will contribute the difference. The batteries will always be supplied with the maximum charge current that they can accept, providing the combined output of solar and the alternator is capable of delivering this and their regulator set points are set correctly.

If the alternator voltage set points are too low, as is typical if you have an unadjustable “dumb” internal regulator, unfortunately it is likely the alternator will charge the battery at a lower than ideal rate, but the solar output will not make this worse. The combined output of the solar and alternator will always be at least as high as the alternator set point will allow (providing the combined output of the solar and alternator is capable of raising the battery voltage to this level).

Don’t worry. The batteries will never be receiving less output from the combined contribution from solar and the alternator than would be possible with the alternator alone.