Efficiency of combined PV and alternator charging.

[BobR]

I am planning my solar/alternator charging system for my powerboat.: [ (2) 230 AH 24 volt Lifepo4 batteries, 70- 100amp alternator, approx 1,000 watt pv panels. This will be installed in the summer of 2023.

My question/ observation is the problem of the alternator regulator seeing the output of the solar panels and thereby reducing the output of the regulator.

Here is a quote from the Balmar site.
"Can I run my alternator, solar panels and/or wind generator at the same time and charge that much faster?
The problem with multiple charging sources is that they tend to fool one another. Say your solar panel (or wind generator) is charging the battery at 14 volts and pushing in 10 amps. You start the engine/alternator up and it sees not the true State of Charge of the battery but 14 volts from the solar panel. The alternator thinks the battery is fully charged and puts out the minimum current (only a few amps). The result is the alternator is not doing anything and the solar is putting in only 10 amps. This condition isn’t damaging to the charging assets, but it is inefficient charging."

Any thoughts will be appreciated.

 

[MisterSandals]

First, you will need a DC to DC charger between your alternator and LiFePO4 battery.
You can set the charging parameters to control the interaction between them.

It is very common to have multiple charge sources, know the charge profiles of each will explain how they behave/interact.

 

[BobR]

Dual

The alternator will be 24 volt and directly charge the Lifepo4 house bank.

The engine has a 12 volt starter and dedicated 12 volt alternator to charge 12v start/windlass battery.

The boat electronics are all 24volt; except starter, windlass, & a backup bilge pump.

 

[BobR]

First, you will need a DC to DC charger between your alternator and LiFePO4 battery.
You can set the charging parameters to control the interaction between them.

It is very common to have multiple charge sources, know the charge profiles of each will explain how they behave/interact.

The problem is to get the 24v solar charge controllers (2) and the 24v alternator to work together.

 

[MisterSandals]

The problem is to get the solar charge controllers (2) and the alternator to work together.

Is your alternator SPECIFICALLY made to charge LiFePO4?

 

[OffGridInTheCity]

Dual

The alternator will be 24 volt and directly charge the Lifepo4 house bank.

As @MisterSandals suggests - you want a DC to DC charger between the alternator and the LifePo4 because the LifePo4 can charge so quickly it can cause the alternator to burn up. This is one of the key differences between LifePo4 and lead-acid - e.g. lead acids don't charge very quickly and the alternator can hook directly.

 

[BobR]

Is your alternator SPECIFICALLY made to charge LiFePO4?

I will be an externally regulated alternator with a regulator that will be lifepo4 compatible.

I was thinking Balmar until I read the above quote.

 

[OffGridInTheCity]

The problem is to get the 24v solar charge controllers (2) and the 24v alternator to work together.

Should not be a problem and they don't need to work together. You can charge a battery from 3 or 10 of 20 different sources at the same time and independently because.... each charger should see the battery voltage and CC/CV (taper off) on their own regardless of what the other sources are doing.

 

[BobR]

As @MisterSandals suggests - you want a DC to DC charger between the alternator and the LifePo4 because the LifePo4 can charge so quickly it can cause the alternator to burn up. This is one of the key differences between LifePo4 and lead-acid - e.g. lead acids don't charge very quickly and the alternator can hook directly.

Smart regulators can be set up to charge lifepo4.

Should not be a problem and they don't need to work together. You can charge a battery from 3 or 10 of 20 different sources at the same time and independently because.... each charger should see the battery voltage and CC/CV (taper off) on their own regardless of what the other sources are doing.

This is for a cruising powerboat with no shore power. Efficiency is important; therefor according to Balmar alternator efficiency suffers with solar input.:
Quote from Balmar:
The problem with multiple charging sources is that they tend to fool one another. Say your solar panel (or wind generator) is charging the battery at 14 volts and pushing in 10 amps. You start the engine/alternator up and it sees not the true State of Charge of the battery but 14 volts from the solar panel. The alternator thinks the battery is fully charged and puts out the minimum current (only a few amps). The result is the alternator is not doing anything and the solar is putting in only 10 amps. This condition isn’t damaging to the charging assets, but it is inefficient charging."

FAQ - Balmar

I am convinced of the benefits of external regulation. Will my (Non-Balmar) alternator work with your MaxCharge (external) regulators? It depends. If the alternator is internally regulated, it needs to be converted to work with an external regulator. See the next FAQ below to learn more. If...

balmar.net

 

[OffGridInTheCity]

Smart regulators can be set up to charge lifepo4.

This is for a cruising powerboat with no shore power. Efficiency is important; therefor according to Balmar alternator efficiency suffers with solar input.:
Quote from Balmar:
The problem with multiple charging sources is that they tend to fool one another. Say your solar panel (or wind generator) is charging the battery at 14 volts and pushing in 10 amps. You start the engine/alternator up and it sees not the true State of Charge of the battery but 14 volts from the solar panel. The alternator thinks the battery is fully charged and puts out the minimum current (only a few amps). The result is the alternator is not doing anything and the solar is putting in only 10 amps. This condition isn’t damaging to the charging assets, but it is inefficient charging."

FAQ - Balmar

I am convinced of the benefits of external regulation. Will my (Non-Balmar) alternator work with your MaxCharge (external) regulators? It depends. If the alternator is internally regulated, it needs to be converted to work with an external regulator. See the next FAQ below to learn more. If...

balmar.net

I believe it - the alternator (and the other chargers) will do less aggressive charging with higher voltage but not sure why this is a problem. Alternator charging = fuel but PV/Wind don't use fuel so I'd tend to favor aggressive PV/Wind over alternator. Also the PV/Wind will not raise the battery voltage from 11 to 14 (all the time) to charge - it will do it in a curve. Maybe 11 to 12 for the 1st hour, 12 to 13 for the second hour etc. So the alternator should be able to get in there.

However, if you want to prioritize alternator over PV/Wind then set the PV/Wind equipment to less aggressive charging by limiting amps (if they have this setting) or lowering the max charge voltage. Either of these will tend to increase the priority of alternator charging.

More on the charging situation....
Let's say it takes Wind and PV and Alternator each 10hrs to fully charge the battery. Wind and PV will not raise the voltage so hi that the alternator does not do it's 1/3. If one of these is a monster - let's say PV can charge the battery in 1hr and the rest take 10hrs, then yes - perhaps it would be so aggressive it would essentially starve the alternator charging.

You haven't said how aggressive each charging source is - but unless Wind (not usually that steady) or PV (not much room on a boat) is way aggressive in it's charging ability - I wouldn't think this would be an issue.

 

[BobR]

I believe the alternator (and all the other chargers) will do less aggressive charging with higher voltage - but not sure why this is a problem. Alternator charging = fuel but PV/Wind don't.

However, one way you prioritize alternator over PV/Wind is set the PV/Wing to less aggressive charging by limiting amps (if they have this setting) or lowering the max charge voltage.

When cruising I usually anchor for several days and want to rely on solar as much as possible. When motoring the engine is usually running around 6-8 hrs.

Even in paradise it gets cloudy.

I do not want to prioritize either; I need them to both work as efficiently as possible.

 

[OffGridInTheCity]

I do not want to prioritize either; I need them to both work as efficiently as possible.

Sounds like they already do

 

[mikefitz]

If the cable and Interconnections are engineered to keep volt drops between chargers and the battery to a minimum then each charger will 'see' the same voltage and deliver the current as if it were an individual charger. Issues arise where excessive volt drops 'fool' the charger. If possible using chargers with a separate voltage sence capability is an advantage.
The Balmar quote may be valid for a badly engineered system with lead batteries, with a well implemented lithium system , where the voltage at the battery stays well below the absorbtion target until the battery is almost fully charged, the quoted issue will not occur.

Mike

 

[GooseF16]

Using chargers for each interface fixes that problem.. several companies make a 12 to 24 volt charger with lithium profile, boost.. The alternator becomes a power supply basically for a DC to DC system.. and if needed you can reverse down from 24 to 12 as needed too.. for example all of Victron's units can charge the same bank. and that 24 volt bank can reverse trickle charge a 12v or provide 12v.. People take absolutes when they talk about fighting... 14.4 to 14.6v boost.. 13.4 to 13.6 sustain float.. done.. pick those numbers based on the 12v specs on a 4S.. convert up as needed.. 28.8 to 29.2v.. smarter folks than me chime in, but I know my MH is using multiple sources now.. it all just works.

 

[wholybee]

To address the main question, about the alternator not working well with Solar. It isn't usually an issue, especially with LFP. With (any) multiple charge source, they will "see" the voltage of the other. But you will get through the bulk charging before the voltage rises enough to make a difference, and there isn't much (if any) time spent in absorption. So, it will add a few minutes probably to charging, but not more than that. Lead Acid has a higher internal resistance, and spends more time in absorption, so it is more of an issue there.

 

[svsagres]

First, you will need a DC to DC charger between your alternator and LiFePO4 battery.
You can set the charging parameters to control the interaction between them.

It is very common to have multiple charge sources, know the charge profiles of each will explain how they behave/interact.

No need for that, you just need a decent regulator. On my boat, my alternator, solar, and inverter/charger all directly charge my LiFePO4 house battery. My lead acid starter battery is kept topped up by a DC:DC charger. Works a treat.

 

[MisterSandals]

No need for that, you just need a decent regulator.

Does that regulate the voltage and/or amps? Is there any concept of bulk/absorb/float or ??
Trying to understand how it works.
Are any of these programmable or made for different battery chemistries?

EDIT:
Found this Aims regulator for lithium. Not sure i want to charge that high. At this price i think i would want a DC to DC charger.
>>
The regulator continuously monitors the input voltage. If the voltage is within the operating range of 9.4 – 14.4V, power will be supplied to the output terminal allowing power to the loads. If the voltage drops below 9.2V or is over 14.6V the power is cut off at the output terminal preventing power to the loads.

 

[svsagres]

I am planning my solar/alternator charging system for my powerboat.: [ (2) 230 AH 24 volt Lifepo4 batteries, 70- 100amp alternator, approx 1,000 watt pv panels. This will be installed in the summer of 2023.

My question/ observation is the problem of the alternator regulator seeing the output of the solar panels and thereby reducing the output of the regulator.

Here is a quote from the Balmar site.
"Can I run my alternator, solar panels and/or wind generator at the same time and charge that much faster?
The problem with multiple charging sources is that they tend to fool one another. Say your solar panel (or wind generator) is charging the battery at 14 volts and pushing in 10 amps. You start the engine/alternator up and it sees not the true State of Charge of the battery but 14 volts from the solar panel. The alternator thinks the battery is fully charged and puts out the minimum current (only a few amps). The result is the alternator is not doing anything and the solar is putting in only 10 amps. This condition isn’t damaging to the charging assets, but it is inefficient charging."

Any thoughts will be appreciated.

If you design things right, it’s not a problem. But what you really want to be looking at is an integrated system. On my boat, my BMS (REC Active BMS) sets the voltage and current limits, and the charging sources (My Alternator, Solar, and Inverter/Charger) all work within that limit. When motoring through harbour with my solar panels out, I’ll get 120W off of those, and 500W off my alternator.

In addition to the REC BMS, the whole thing is managed by a Victron Cerbo GX, which in turn is controlling my two solar MPPTs, and my Inverter/Charger. In addition, my alternator is managed by a Wakespeed WS500 regulator, which is also controlled by the BMS. It works beautifully together.

However what Balmar wrote there is patently absurd. The voltage that the regulator will see is the voltage of the battery. It doesn’t matter whether the solar is feeding in 10A or whatever, the voltage is the voltage. This is doubly true with LFP, as the internal resistance of the batteries is so low. If I had the charging capability, I could dump 120A into my battery, and it would only go up a fraction of a volt.

The other reason why it’s nonsense is that Voltage is a really piss poor way to determine the State of Charge of a LFP battery due to the stupidly flat charge curve. You need more sophisticated equipment to get that with any level of reliability.

 

[svsagres]

Does that regulate the voltage and/or amps? Is there any concept of bulk/absorb/float or ??
Trying to understand how it works.
Are any of these programmable or made for different battery chemistries?

Yes. It connects to my BMS via CAN Bus, and will throttle/limit itself based on direction from the BMS. During the bulk stage, my BMS typically sets the limit to 14.5V and 120A. I can never actually hit that with my setup, so my alternator is typically pushing 40A or so (I deliberately derate it since I’m on a little 10HP diesel).

As the battery comes towards full, the BMS will drop the current limit, and the regulator will comply. After a bit, it then drops the voltage limit down to 13.8V, so after the battery is drawn down, the alternator will just sit there powering the house loads and keep the current in/out of the battery at 0A.

Throughout the whole situation, the regulator is also watching the temperature of the alternator, if it gets too hot, it will also back off the field to keep the temperature within limits.

If it’s not running with external control, the charge curves are all configurable, so it will work with whatever chemistry you want.

 

[MisterSandals]

my BMS (REC Active BMS) sets the voltage and current limits, and the charging sources (My Alternator, Solar, and Inverter/Charger) all work within that limit.

Ah yea, thats a pretty fancy and spendy system! Definitely the Lamborghini install.