Many here say that an alternator should not be connected to LiFePO4 and that one should use DC-DC Charger

[l00semarble]

I understand the reasons. A stock alternator directly connected to Lithium is a problem as the low internal resistance will cause high continuous currents and kill the alternator by heat. But many (most?) serious cruisers who rely on an alternator for significant battery charging will have a high output/heavy duty alternator and an external regulator (such as Balmar setup.)

The beloved Victron DC-DC charger is great and often recommended as the solution for DC-DC charging of a LiFeP04 bank from the alternator on starter lead acid bank. This makes sense and is safe/conservative but at 12v you are limited to 30 amps which is a joke if you have a 120a, or 150a or perhaps even larger alternator. Balmar XT series goes to 250a in a small case alternator. It would be such a waste to have a huge honkin' alternator and only use 30a of it.

yes you can parallel the DC-DC charger but if you want to make good use of a 150a alternator you would need 5 of them in parallel which is totally impractical.

Even with a bone stock alternator rated at 60-80a putting a 30a DC-DC charger is going to cripple recharge rates which could really impact a cruiser's lifestyle if they have no generator and are using the alternator as a primary charging source.

Obviously any other solution has to keep many different factors in mind. A alternator temp sensor on regulator is critical and not allowing any chance of a BMS open circuiting a alternator is also critical. But there are ways to do this other than an undersized DC-DC charger.

Why is this always the "go to" recommendation? Just because it is easy to be safe despite performance?

 

[l00semarble]

Not picking on anybody in particular but this was put out as a "you have to" mandate twice in a recent thread. Yes it may be a good option in some cases but it it not the only option and can be very limiting.


https://diysolarforum.com/threads/e...-pv-and-alternator-charging.53005/post-675219

Efficiency of combined PV and alternator charging.

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...

diysolarforum.com

 

[BentleyJ]

I agree with your thinking. I installed 2 CyclenPo LFP, 50Ah automotive starting batteries in a 2005 Dodge ram Diesel. After checking the alternator with a Fluke meter and determining it was 14.0 to 14.1V, which is enough to fully charge them. I decided to go without a DCDC converter or charger because I don't intend to camp or cycle the batteries when the vehicle is not running. The batteries are only for starting so will never get to a very low SoC that would require high charging current exceeding alternator output. After 3 years they are working just fine and the original alternator that now has 350,000 miles on it is hasn't failed.

 

[Browneye]

One poor fellow here with a sailboat has fried five of those alternators. So if you're going the same route make sure you don't cook your alternator. Seems the problem is at low speed or idle, where the battery(s) don't know better than to pull the full 100A or whatever you've set your regulator for, which overheats the alternator since it is designed to put out more amps at speed where it gets some cooling.

Run it, test it, make sure you're getting what you want out of your setup.

 

[OffGridInTheCity]

I found this youtube pretty detailed / good info charging of LifePo4. For example, at 3:00... you can see 1500 RPM / 65a on a regular alternator starting to smoke. At 3:20... they start testing a Balmar alternator.

Provides info for thought

 

[wholybee]

I don't think ANYONE suggests that a DCDC is *required* or the ONLY solution. A DCDC charger is a great option if you have a stock internally regulated alternator, and want to do a budget install with an inexpensive drop-in. If you are building a larger bank, with larger alternators, then pretty much everyone agrees the best way is with a purpose-built alternator with a blamar or wakespeed regulator. A balmar alternator and regulator could add over $1000 to a Lithium installation.

A couple considerations. A bone stock 60A alternator really should not be run at more than 30A. The BEST you can do is use a temp sensor to allow it to run at 60A for 10-20 minutes, and then reduce it to 30 when it gets hot. The difference between those two options is very small, less than 10Ah difference put back in the battery over what might be a couple hours of charging.

Purpose built alternators like a Balmar are not only 100A+, but they are designed to run at a lower RPM, and with less airflow. Compared to an automotive or RV alternator that is 100A, runs at higher RPM, and has lots of airflow from driving down the street.

Even with a Balmar or similar, a temp sensor is needed, as they will not run at full power for more than a few minutes. That 100A alternator is going to be regulated down to 60-70 by the temp sensor if it has good cooling. 50A or less if the engine room has poor ventilation.

The BEST answer is solar. Solar works great with LFP, far better than it does with LA.

This is all assuming a BOAT. You can get away with a lot more in a car or RV, because they run at higher RPMS, and have excellent cooling. Just because someone in an RV uses a stock alternator with no special considerations does not mean that will work on a boat.

 

[svsagres]

Why is this always the "go to" recommendation? Just because it is easy to be safe despite performance?

For better or worse, it seems like a lot of people here are trying to do things “on the cheap.” In those situations, it really is probably the best choice. If you’re just going to kludge together some LFP “Drop-ins” that can’t control their charging process, the safest thing to do is use a DC:DC that won’t complain if the load suddenly drops.

If you’re building a decent, integrated system, the best choice at this point is a Wakespeed.

I didn’t bother buying a fancy alternator, instead I had a donated 85A Mitsubishi rebuilt and modified for external regulation by my local starter/alternator shop. I can continuously pull 60A out of it, and not hit more than about 75C. Most of the time, I run the alternator at half power and am happy to get 40A and more power to my prop (Little 10HP single cylinder diesel).

 

[Joe Delaney]

I understand the reasons. A stock alternator directly connected to Lithium is a problem as the low internal resistance will cause high continuous currents and kill the alternator by heat. But many (most?) serious cruisers who rely on an alternator for significant battery charging will have a high output/heavy duty alternator and an external regulator (such as Balmar setup.)

The beloved Victron DC-DC charger is great and often recommended as the solution for DC-DC charging of a LiFeP04 bank from the alternator on starter lead acid bank. This makes sense and is safe/conservative but at 12v you are limited to 30 amps which is a joke if you have a 120a, or 150a or perhaps even larger alternator. Balmar XT series goes to 250a in a small case alternator. It would be such a waste to have a huge honkin' alternator and only use 30a of it.

yes you can parallel the DC-DC charger but if you want to make good use of a 150a alternator you would need 5 of them in parallel which is totally impractical.

Even with a bone stock alternator rated at 60-80a putting a 30a DC-DC charger is going to cripple recharge rates which could really impact a cruiser's lifestyle if they have no generator and are using the alternator as a primary charging source.

Obviously any other solution has to keep many different factors in mind. A alternator temp sensor on regulator is critical and not allowing any chance of a BMS open circuiting a alternator is also critical. But there are ways to do this other than an undersized DC-DC charger.

Why is this always the "go to" recommendation? Just because it is easy to be safe despite performance?

typical cruising sailboats have tiny engines, in my case a 40hp perkins in one boat and a 50hp Yanmar in another. Assumingyou've converted to a double pulley oy serpentine belt to drive a 150a or 250a aletrnator, also consider that it will tale between 10 to 20hp to drive those alternators,
when your boat tops out at 6-7kts with all power available, compound that with an outgoing tide your fighting or just a straight headwind, you can actually be motoring backwards, so I often recommend going back to the stock alternator with an interrupt switch in line with the exciter circuit mounted close to the helm.
and add an alternate charging source, a genset, solar or wind.

 

[l00semarble]

typical cruising sailboats have tiny engines, in my case a 40hp perkins in one boat and a 50hp Yanmar in another. Assumingyou've converted to a double pulley oy serpentine belt to drive a 150a or 250a aletrnator, also consider that it will tale between 10 to 20hp to drive those alternators,
when your boat tops out at 6-7kts with all power available, compound that with an outgoing tide your fighting or just a straight headwind, you can actually be motoring backwards, so I often recommend going back to the stock alternator with an interrupt switch in line with the exciter circuit mounted close to the helm.
and add an alternate charging source, a genset, solar or wind.

Your HP numbers are a bit exaggerated, no?

150a * 14.4v = 2,160w
2,160w / 746w/hp = 2.9hp

Yes, of course there is loss but to use 10hp that would imply that for every watt made greater than 3w was lost.

Obviously (to me anyway) I was using extreme examples of alternator size but it is quite common to fit a 100a Balmar to a very small diesel like yours and we can do so even with stock single-v belt. But the point of my post remains: a DC-DC charger to charge the LiFePO4 from this alternator would cripple the system.

The DC-DC charger should be used the other way around to charge the start battery.

 

[wholybee]

typical cruising sailboats have tiny engines, in my case a 40hp perkins in one boat and a 50hp Yanmar in another. Assumingyou've converted to a double pulley oy serpentine belt to drive a 150a or 250a aletrnator, also consider that it will tale between 10 to 20hp to drive those alternators,
when your boat tops out at 6-7kts with all power available, compound that with an outgoing tide your fighting or just a straight headwind, you can actually be motoring backwards, so I often recommend going back to the stock alternator with an interrupt switch in line with the exciter circuit mounted close to the helm.
and add an alternate charging source, a genset, solar or wind.

Assuming 50% efficiency, 250A x 13 V = 3250W / 50% = 6500W
1 Hp = 745W
6500W / 745W = 8hp at full output.

And that is a huge 250A alternator at its max output. A more reasonable 125A would only be 4hp. Since it would quickly be cut back due to heat after 20 minutes, a 125A alternator putting out 65A would only be 2 hp. Having an on/off switch isn't a bad idea for several reasons. However, with a 40 or 50 HP engine you should not feel the effect of a 125A alternator, and while you might feel the 250A, it would not be crippling unless you were already underpowered. A sailboat should reach hull speed well below the full power output of the engine.

That said, some small boats only have a 10 hp engine, which does pose a problem with a large alternator. Balmar regulators have a small engine mode that can be activated with a switch. So, if you need the extra power from the engine, you can activate small engine mode and still have a working alternator, just not pulling so much power from the engine.

 

[DPC]

high continuous currents and kill the alternator by heat

Alternators are not good battery chargers for any application.
The right way to charge a battery requires you to limit the charge current to a level the battery can except for its state of discharge.
Alternator regulators try to regulate voltage only.

Also your likely to smoke the regulator before the winding's but it depends on the unit.

Summer of 87 I built a set with a 5 hp Briggs and 150 amp leece nevile to charge batteries.
It worked but I burned up a lot of regulators and if the batteries were ina deep state of discharge the engine had a very hard time

The corrrect thing would have been to use some sort of external regulator with a current limiting function but I was young and didn't know any better.

Then we got the first small solar panels in the 90s.
Small but wow great.
The trick to using the alternator was to carry through those periods when the sun was not enough and before the batteries became to deeply discharged.

Today this same system is still running.
Burning gas infrequently and soon to be replaced in a complete modern upgrade.
I will still keep an MG set but it might not be an alternator.
I might go with a PM head and electronic load control

 

[DPC]

Assuming 50% efficiency, 250A x 13 V = 3250W / 50% = 6500W
1 Hp = 745W
6500W / 745W = 8hp at full output.

Try and pull start that.
You might get lucky of you have a modern alternator with a soft start function.
if you don;t have a soft start built into the regulator that engine is really going to suck wind struggle to get up and into some torque

That very high current is going to be very hard on the alternator and motor.

 

[DPC]

This is a Chinese electric vehicle range extender.

Nothing like it on this side of the pond I am aware of and no venders of this style of generator charger.
It uses a PM head so there is no need for field control.
The voltage and current regulation is managed by a computer that monitors both and controls engine speed and torque through a stepper motor on the carb ( no single speed mechanical gov here )

This is how you charge a battery with a gas engine.....

 

[time2roll]

Why is this always the "go to" recommendation? Just because it is easy to be safe despite performance?

The go to solution is to engineer a system that works reliably. Every vehicle and situation is different.
We can help if there is a specific situation but no chance to have something that is the end all perfect solution for every application.

 

[wholybee]

Try and pull start that.
You might get lucky of you have a modern alternator with a soft start function.
if you don;t have a soft start built into the regulator that engine is really going to suck wind struggle to get up and into some torque

That very high current is going to be very hard on the alternator and motor.

Any 250A alternator is going to be externally regulated and the do often have soft starts, ramping up the field current slowly. Also, they don't produce full power at low rpm, so the engine can start making power before the load comes on. This is a very common application and its been worked out.

 

[wholybee]

Alternators are not good battery chargers for any application.
The right way to charge a battery requires you to limit the charge current to a level the battery can except for its state of discharge.
Alternator regulators try to regulate voltage only.

Also your likely to smoke the regulator before the winding's but it depends on the unit.

Summer of 87 I built a set with a 5 hp Briggs and 150 amp leece nevile to charge batteries.
It worked but I burned up a lot of regulators and if the batteries were ina deep state of discharge the engine had a very hard time

The corrrect thing would have been to use some sort of external regulator with a current limiting function but I was young and didn't know any better.

Then we got the first small solar panels in the 90s.
Small but wow great.
The trick to using the alternator was to carry through those periods when the sun was not enough and before the batteries became to deeply discharged.

Today this same system is still running.
Burning gas infrequently and soon to be replaced in a complete modern upgrade.
I will still keep an MG set but it might not be an alternator.
I might go with a PM head and electronic load control

This has been solved with modern regulators designed for large batteries or LFP. Wakespeed has multiple charging stages, a current sensor as well as voltage, and a temp sensor on the alternator to reduce output if it gets too hot.
A stock alternator or a cheap high output alternator that is little more than a stock alternator wound for more current and you get the problems you describe. Build the system for the job it needs to do, and no issues.

 

[wholybee]

This is a Chinese electric vehicle range extender.

Nothing like it on this side of the pond I am aware of and no venders of this style of generator charger.
It uses a PM head so there is no need for field control.
The voltage and current regulation is managed by a computer that monitors both and controls engine speed and torque through a stepper motor on the carb ( no single speed mechanical gov here )

This is how you charge a battery with a gas engine.....

How is this different from a honda inverter generator?

 

[DPC]

How is this different from a honda inverter generator?

A Honda Generator generates AC power at a fixed voltage and you need to provide a battery charger to charge the batteries.
The electric vehicle rang extender cuts out the middle man and generates and rectifies the correct voltage and regulate the correct amount of current in one shot.

All it does is charge batteries, no compromises ( and it starts and stop automatic depending on need )

 

[DPC]

Wakespeed has multiple charging stages, a current sensor as well as voltage, and a temp sensor on the alternator to reduce output if it gets too hot.

Sounds good, but thats an aftermarket part for an automotive alternator.
I would rather control the output based on RPM than field control like this to save fuel.
And I rather have a unit designed from the start as a battery charger and not a voltage maintainer with extra bits added.
That's why to get back to your Honda inverter units.... why they change speed with load rather than just excitation like older units.

I don't know anything about Wakespeed or their regulators, but I have seen some marine regulators with multi stage charging.
They are much better than automotive units.

 

[wholybee]

Sounds good, but thats an aftermarket part for an automotive alternator.
I would rather control the output based on RPM than field control like this to save fuel.
And I rather have a unit designed from the start as a battery charger and not a voltage maintainer with extra bits added.
That's why to get back to your Honda inverter units.... why they change speed with load rather than just excitation like older units.

I don't know anything about Wakespeed or their regulators, but I have seen some marine regulators with multi stage charging.
They are much better than automotive units.

Wakespeed was designed from the ground up for the marine market. It isn't an automotive unit. It will also connect to a BMS via Canbus to allow the BMS to control the alternator. 3 stage charging, using a shunt to detect tail current to change stages. It is not a "voltage maintainer." It is undoubtably "smarter" than the gas engine charger you show.
If you are running the engine to propel your boat, adjusting engine speed isn't a very good option. Also, diesel engines have a narrow RPM range where they are efficient. That is why you don't see inverter generators that are diesel, but the concept works well with gas.
I doubt that a good inverter generator connected to a high quality Victron charger is any less efficient than a dedicated unit like you show. And I sure rather charge my $3000 LFP bank with a Victron than an unknown gas charger thingy. And I rather charge with a Balmar or Wakespeed regulator than they gas thingy also.

Do you have a link to the specs?