diy solar

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Let's melt some alternators

Turd Furguson

it's a funny name.
Joined
Jan 27, 2020
Messages
64
Charging LifePo4 with an alternator will melt it.

This is true, but what about high-amp units that are designed for smarter charging with an external regulator?

Consider an alternator controlled by a Xantrex XAR that has variable settings for voltage, current, etc. It also has temperature control which prevents overheating. Victron demonstrates similar capabilities for Balmar in this video:

https://www.victronenergy.com/blog/2019/10/07/careful-alternator-charging-lithium/

With the exception of PRG-2 & PRG-5 in the table below for the Xantrex unit, a LifePo4 battery would never achieve a maximum charge at 14.6v, or higher, that would threaten approaching a high-voltage shutdown by the BMS. 100% SOC couldn’t be achieved but we are close enough at the PRG-4 setting of 14.4v. PRG-1 gives more buffer for increased comfort.

Capture.JPG

This controller can also limit maximum current as a percentage of alternator capability from 40-100%. So, if we didn’t want to rely on thermal throttling entirely we could limit output to 40amps as an example, aligning with a DC-DC converter.

Given this, how is direct LifePo4 charging a significant risk over a deeply-depleted SLA bank when you’re not seeking a full 100% SOC? From what I see, current limiting & temperature control is already provided by the alternator controller, and risk of a high-voltage disconnect is very low as we’d never get there on a bulk charge profile under 14.6v.

Risk of disconnect in this scenario isn’t much different than pulling the cables on an SLA bank. We can also leverage the full output potential of the alternator if/when the conditions support it.

DC-DC chargers are recommended in many articles - these could load an alternator similarly and we’d rely on the same thermal throttling to protect it. Therefore, this device would only serve to prevent a disconnect scenario that is mitigated by a voltage setting below 14.6; we can also control alternator current as mentioned above to the same 40amps if desired. DC-DC chargers also introduce another box and potential point of failure in the system.

I see the overall risks & problems with alternator charging reduced significantly if you're not chasing maximum charge.

Thoughts?
 
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The percentage control is cool.
I’m planning on putting a balmar mc-614 on my modified stock 51Amp alternator in my sailboat with a universal m3-20b Diesel engine. No LA battery, straight from the regulator to my 12v 200ah lifepo4 bank. Don’t need to throttle back my alternator since it’s already puny. Realistically, it will never be flat out charging for more than 3 hours, and the regulator will dial it down even then. I’ll post about the setup when it’s complete.
 
I contacted Balmar to understand their LifePo4 profile and how they handle a HVD scenario….They don’t and also expect HVD to be an exceptionally rare event.

Their recommendation is to ensure alternator shutdown prior to a battery disconnect, further outlined in this service bulletin:

http://www.balmar.net/wp-content/up...-Battery-Charge-Programming-December-2017.pdf

While not as customization as the Xantrex you can enable the ‘Small Engine Setting’ to limit charge capacity to 50%. Current is temperature-regulated as noted above.

A battery disconnect scenario should never occur in normal operating conditions and an alternator (should) behave no differently than charging a depleted SLA house bank with its temperature-controlled throttling.

I see value in a small DC-DC charger back to the starter battery (i.e. a Digital Echo), but not vice-versa as you forfeit potential charge capacity on the house bank.
 
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Current limiting is the only way to safely charge LiFePO4 batteries with an alternator. I made my own controller with current limiting (for my own use, not a commercial project). A separate lead-acid starter battery (if it is only used for starting the engine) requires very little charging and a small DC-DC charger is indeed the way to go (charge only when the engine is running, i.e. switched on/off by the alternator diode trio output.

My only concern is that if the BMS fails and an abrupt disconnect of the LFP batteries takes place, before the alternator controller stops the field current when the max charge voltage has been reached, the consequence will be blown alternator diodes. I still have to find a satisfactory solution for this. Maybe do away with BMS altogether, just use a balancer en a separate low V and low T disconnect. Ideas very welcome.

 
Agreed, but this LI-MB225 is designed to work with LIFEPO4 but it simply cuts them out after ~15 minutes then back on some time later and repeats. I asked if they had some sort of "soft" relay for that, but they don't. It's just a hard on/off.

So how would that work if what you say is correct about alternators frying when BMS cuts the batteries off?
 
I don't know. All I know is that alternator charging can only safely be stopped by cutting the field current (excitation current).
 
Walt - that is very cool. You've essentially created your own smart alternator charger with the ability to customize settings and interface with an NMEA multiplexer. Any chance you'd consider open-sourcing the plans/schematics on GitHub or similar? I'd love to support it.

Are you limiting current via resistance on the field voltage?

In the case of BMS failure or abrupt disconnection there's this option; cheap and effective should an HVD occur.

https://www.sterling-power-usa.com/SterlingPower12voltalternatorprotectiondevice.aspx

We talk about HVD on here like its a normal & expected thing... this should be an extremely rare occurrence if something in the system is failing. 14.6v is maximum charge (4x 3.65v cells) but if we are limiting our charge currents to less (i.e. the Xantrex specs in my first post) we'll never get there. Most BMS' also have a bit more headroom before considering an HVD.

Interesting discussion and exactly what I was hoping for... Let's keep it going!
 
Use a Bogart SC-2030 as a current limiting (30 Amps) DC-DC charger - DC source may be an alternator or a 30 Amps, 15 Volts SMPS type power supply

 
Current limiting is the only way to safely charge LiFePO4 batteries with an alternator. I made my own controller with current limiting (for my own use, not a commercial project). A separate lead-acid starter battery (if it is only used for starting the engine) requires very little charging and a small DC-DC charger is indeed the way to go (charge only when the engine is running, i.e. switched on/off by the alternator diode trio output.

My only concern is that if the BMS fails and an abrupt disconnect of the LFP batteries takes place, before the alternator controller stops the field current when the max charge voltage has been reached, the consequence will be blown alternator diodes. I still have to find a satisfactory solution for this. Maybe do away with BMS altogether, just use a balancer en a separate low V and low T disconnect. Ideas very welcome.

This may be an answer to your fear of serge or spike caused when the BMS goes off line abruptly, more applicable to larger high output alternators over 100 amps https://electromaax.com/Marine-Batteries/adid/14703107/ElectroMaax-System-Surge-Protector
 
Good post. Thanks for your very important message. I'm using a Balmar mc-614 with a small engine mode switch switch so I can decrease the output of my balmar 100a alternator by 50% if when I'm charging my home made 180ah Calb lifepo4. See time location 6:04 in this video.
 
The percentage control is cool.
I’m planning on putting a balmar mc-614 on my modified stock 51Amp alternator in my sailboat with a universal m3-20b Diesel engine. No LA battery, straight from the regulator to my 12v 200ah lifepo4 bank. Don’t need to throttle back my alternator since it’s already puny. Realistically, it will never be flat out charging for more than 3 hours, and the regulator will dial it down even then. I’ll post about the setup when it’s complete.
I think best practice is not to run your alternator at full with lifepo4. Not sure if you intend to run it full bore for hrs. This article is bible to me. See the alternator section https://marinehowto.com/lifepo4-batteries-on-boats/
 
In my case with my new system I choose to keep my LA starting battery to buffer the spikes.

Agree with this. Yes, you can buy a fancy alternator at 3x the cost of the original, if you really need it. Yes, you can also buy a good external controller and play with lowering the output current - so why from the first place did you get a bigger alternator? And why create another potential failure point and pay for all that?

My idea is similar and really not to be cheap, but as a way to maintain simplicity and reliability - keep everything as is and use a good DC-DC 50A charge controller to charge the LFP home bank from cranking and backup AGM bank circuit. I’m actually going to keep even the old AGM home bank until everything works the way it should. The only extra here can be some switches and bus bar duplicates to separate the new output from the old and slowly move each client from the old to the new while monitoring the effect on the new LFP array.

Am I missing anything here?
 
Current limiting is the only way to safely charge LiFePO4 batteries with an alternator. I made my own controller with current limiting (for my own use, not a commercial project). A separate lead-acid starter battery (if it is only used for starting the engine) requires very little charging and a small DC-DC charger is indeed the way to go (charge only when the engine is running, i.e. switched on/off by the alternator diode trio output.

My only concern is that if the BMS fails and an abrupt disconnect of the LFP batteries takes place, before the alternator controller stops the field current when the max charge voltage has been reached, the consequence will be blown alternator diodes. I still have to find a satisfactory solution for this. Maybe do away with BMS altogether, just use a balancer en a separate low V and low T disconnect. Ideas very welcome.

I have my alternator charging both my house bank and start battery through a relay. If my BMS were to disconnect because of an over voltage or max voltage situation, the start battery would still be online to save the diodes.
 
In the case of BMS failure or abrupt disconnection there's this option; cheap and effective should an HVD occur.

https://www.sterling-power-usa.com/SterlingPower12voltalternatorprotectiondevice.aspx

We talk about HVD on here like its a normal & expected thing... this should be an extremely rare occurrence...

Interesting discussion and exactly what I was hoping for... Let's keep it going!

Has anyone tried this $70 Sterling alternator protection device and know if it works? It's sacrificial and needs to be replaced occasionally right?

My outboard engine alternator only puts out 50 or 60 amps at 14v and change so I'm hoping HVD will not happen, but I HAVE heard of guys with my setup hitting HVD and loosing all accessory power too. That's a concern, navigation all needing reset.

I don't think a $370 ElectroMax surge protector is necessary in my little setup, am I correct? I plan to keep my 120Ah LifePO4 cranking battery below 80% SOC as well for life cycle enhancement and to eliminate HVD. Maybe a separate port bms with a SSR on the charge port to the engine, and all accessories on the load port? Sounds good on paper but anyone try that?
 
I have a flooded start battery and a LFP house battery. They are connected through a relay when voltage exeeds 13.4v. I am working on the theory that if a get an HVD the start battery will absorb the spike and save the alternator. I have read both pros and cons on this approach. But I also Figure I’ll keep my charge output under 14.1v so I won’t reach HVD and treat my batteries better.
 
I have a flooded start battery and a LFP house battery. They are connected through a relay when voltage exeeds 13.4v. I am working on the theory that if a get an HVD the start battery will absorb the spike and save the alternator. I have read both pros and cons on this approach. But I also Figure I’ll keep my charge output under 14.1v so I won’t reach HVD and treat my batteries better.

I'm pretty sure that's currently (no pun intended) the best way to buffer the alternator. I unfortunately don't have room for separate start and house batteries, and I'm trying to save weight by just going with a bigger LFP battery and an alternator protection device...
 
I have a flooded start battery and a LFP house battery. They are connected through a relay when voltage exeeds 13.4v. I am working on the theory that if a get an HVD the start battery will absorb the spike and save the alternator. I have read both pros and cons on this approach. But I also Figure I’ll keep my charge output under 14.1v so I won’t reach HVD and treat my batteries better.

Seacap - what relay are you using? I'm about to build a 720ah LFP house bank. I was planning to move my current LifeLine 4D AGM to be my starter battery, so your relay could be what I need to help this HVD issue.

Currently I have a Duo-Charge (B2B 4amp dc/dc charger) from the house bank to the starter battery and a second Duo-Charge from house bank to bow thruster battery.
 
I have my alternator charging both my house bank and start battery through a relay. If my BMS were to disconnect because of an over voltage or max voltage situation, the start battery would still be online to save the diodes.
My guess is that by using DC-DC charger, even if the BMS fails in a way that it directly connects the LFP to the charging (sounds like very unusual failure, the more common will be a disconnection of the LFP) - the DC-DC charger limited to its rated current (Way under the alternator output) should protect the alternator and the cranking battery.
Comments are more than welcome!
 
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