Connecting LifePo Batteries to Delco Remy 50dn Alternator...

[mqbus767]

I'm trying to figure out the best method to connect my 50dn alternator to my LifePo batteries. First, allow me to layout the components in play:

• A Delco Remy 50dn alternator (24v 270amps) - http://www.delcoremy.com/alternators/find-by-model-family/50dn
• 6x12v 100ah Battle Born LifePo batteries in 3x2 series/parallel for 24v (300ah)
• 2 Group 8D 12v starter batteries in series

Battle Born has told me that it should be fine to simply use a relay (auto or manual) to connect the starter batteries to the house bank, but for multiple reasons, I'm not sure I want to do that:

• My understanding is that Lithium batteries have a very low internal resistance and thus, when deeply discharged, could potentially draw a very large load to charge up again. (Maybe up to the maximum AH of the battery bank)
• I certainly do not want to run wire capable of handling 250+ amps from my start batteries to the lithium batteries.
• The alternator, obviously, does not abide by the optimum charge profile for LifePo batteries.

I believe the correct solution includes a DC-DC battery charger. In theory, a DC-DC charger designed for LifePo batteries could provide phased charging and voltage correction to insure that no damage is done to the batteries. I've researched several chargers from Victron (Orion), Sterling, Renogy, and MasterVolt. The issues with most of the chargers is relatively low output (30amps or less). Because my intention is to run my mini split while running down the road, I'd like to get as much out of the alternator as I can. Afterall, I've removed nearly all of the heavy load DC devices from the bus. (i.e. fans, lights, metro gear, etc.)

The one exception to the list is the Sterling model AB24100 https://www.sterling-power-usa.com/24volt100ampalternator-to-batterycharger.aspx. This charger includes 4 stage, LifePo aware charging profiles and claims to output 100amps. At first glance, it looks perfect. However, when reading the install manual, there is this little warning:

Before connecting the unit to your alternator(s) make sure that your alternator-to-battery charger is rated for the maximum output of the alternator(s) total combined ( if 2 are used ) current.

This seems to indicate that not only is this particular model too small, even their next unit up (AB24200) may not be "rated" to handle the 50dn. And even if there was a model capable of handling 300amps, the wire would be so egregiously large, it would hardly be worth wiring it all together. Please feel free to correct me on these assumptions; I'm certainly not an electrical engineer.

Keep in mind that I have reached out to multiple vendors and have either not yet received reply or received replies that do not fully satisfy the questions. So, I have the following questions for any that might know:

• My understanding is that a DC-DC charge controller, limits the current going from one side to the other. Why all this fuss about input current if the unit is designed to only charge at some designated amperage?
• Is this input current warning perhaps only applicable in cases where the charger is directly connected to the alternator?
• Would not, in my case, the starter batteries act as a sink for any extra current in the system once the house batteries are charged?
• Does anyone out there have experience doing this with their heavy alternator and Lithium batteries?
• Is there a smarter/better way to accomplish this?

If you're so inclined to investigate Sterling's charger, here's a link to the install/owner manual:

https://www.sterling-power-usa.com/library/Alternator%20to%20Battery%20Charger%20Owners%20Manual%20and%20Installation%20Instructions%20for%20all%20models%20excluding%20AB12130.pdf

Their wiring diagrams show clearly that this device is designed to sit between the alternator and batteries. My intended use would be to source the charger from the + terminal of the start battery and only use one side of the charger. The manual does state:

If you are only going to charge one bank of batteries, then use the
"DOMESTIC BATTERY" output only. The "START BATTERY" output can remain unused without affecting the performance of the unit.

Thank you for any and all feedback. It's much appreciated.

[richard5933]

I've been running a Sterling BTB charger to charger our 12v house bank from our 24v bus 50DN for years with no problem.

Not sure why the output of the 50DN is a concern here. My understanding is that they don't 'push' current to devices, but rather devices 'pull' current from them. Otherwise, you'd never be able to connect any device to a 50DN that couldn't handle all the possible output from it.

Our Sterling can pull a max of 35 amps @ 24v and output a max of 70 amps @ 12v and obviously our 50DN is capable of outputting much more than 35 amps.

I'd have no problem doing what you're planning.

The US rep for Sterling is quite responsive to questions, so I'd suggest that you give him a call if you're unsure.

[luvrbus]

All the the new RV class A  and bus conversions like Liberty using LifePo are using a separate alternator completely separate of the chassis system but that could be and probably is because of all the sensitive electronics on the chassis with the CAN system       

[thomasinnv]

I currently have a 400 ah @ 24 volts lifepo4 house bank. I charge the bank from the 50dn while under way using a 400 amp relay controlled by a magnum SBC. (The sbc keeps the engine batteries full while parked, and a relay enrgized from an ignition source controls wether or not the big 400a relay is online or offline. This way the 400a relay only engages when the engine is running and the sbc sees a charging source.) After some experimenting I have found that it works quite well with the voltage regulator set at about 27.6 no load. The lifepo4 bank doesn't pull more than about 50 amps even when soc is very low. The trick is in the voltage, the higher you set the voltage, the higher the amp draw. If i switch on an ac unit or two while under way, the 50dn carries them no problem and the battery bank still gets its charging.

[Fred Mc]

My understanding is that with regular automotive alternators(don't know if this applies to the DN50)the lithium batteries can draw so much power that the alternators are overworked and will overheat eventually destroying them. I asked this question on a lithium discussion blog but didn't get a definitive answer.

[mqbus767]

Great information guys. Thanks for the real world thomasinnv! Your experience with your LifePo4 batteries seems to contradict what others are saying about low SoC and current draw. Are you ever worried that under very low SoC (10%) your bank will pull more amps than your your relay connecting wires can handle? I currently have 2AWG from the starter batteries to my electrical bay, so I'm not wanting to pull much more than 100 amps continuously through it.

I got in touch with Adam at Sterling Power USA today and he said that the unit I was considering (AB24100) is not what I would need for two reasons: 1. The charge profiles are not inline with what LifePo batteries need. 2. The 50DN (24v at 270amps) is too large for the AB24100 (rated up to 100amps). He recommended their B2B charger model number BB242435, but it's only 35amps. I could run two of them in parallel, but they are pretty pricey to start doing that.

If my research is correct, my mini split system (https://www.ajmadison.com/cgi-bin/ajmadison/LMU24CHV.html) draws up to 1480 watts in cooling mode and 1800 in heating. This means I'll need around 100 amps from the alternator to run the mini split and not dip into the battery bank while running down the road.

I also called Battle Born again and got in touch with a gentlemen named Eric. Super helpful and spent 15-20 minutes on the phone with him talking over options. He's recommended looking again at smart battery combiners, so I'll go back and again research them. He suggested looking at Victron's Cyrix Lithium series, Balmar's MC624, and one by a company I've never heard of; Wakespeed.

I certainly like the simplicity and efficiency of a relay over a B2B charger. It seems like the market for these switches is just now coming up to speed with Lithium battery peculiarities.

[RichardEntrekin]

Thomas did not contradict the conventional wisdom that LiPo banks can fry your alternator. Repeating what was said. the current into the LiPo bank can be controlled through the voltage setpoint on the alternator regulator. You would have to experiment with the voltage setpoint, and your bank. Set the voltage high enough on the alternator, and the bank could easily draw 2 to 3 times it's nameplate capacity. It's not a precise way of charging the batteries, but physics is physics.

You sort of have listed three requirements that don't want to play well with one another. Limit the current output of the alternator, run mini split with engine alternator, and no desire to install 4/0 battery cables.

You do have the 50DN working for you. Most setups have a much lesser alternator. I am assuming yours is oil cooled?

I really like Thomas's solution for simplicity and safety. Use a 400 amp continuous duty solenoid to merge the alternator to the LiP0. If possible find a way to monitor the temp of the alternator so that you can switch the solenoid off if it starts to overheat.

I just don't think the DC to DC chargers out there were intended to power an AC unit while going down the road.

There is a very good reason the Prevost converters are using a separate alternator to power their LiPo setups. They run into the same problem you have outlined.

I don't run my AC's off the engine. I do have a 1000 Ahr bank that I have had for 6 years. I have the merge/disconnect solenoid. And I hardly ever use my engine alternator to charge the LiPo's.

My .02, and not the gospel.

[mqbus767]

Thanks for the input Richard. Yes. My 50dn is oil cooled.

I had read about voltage regulation also controlling the current draw of the batteries, so that's finally clicking in my mind now. I've decided to go with the Cyrix Lithium series smart relay (https://www.victronenergy.com/upload/documents/Datasheet-Cyrix-Li-ion-230-A-EN.pdf) for now, so we'll see how that works for me. I'll report back after some tests.

[mqbus767]

Installed the Cyrix battery combiner today. The install is very straight-forward; before the Quattro, positives of the start and house batteries, and a ground wire to the start battery to measure voltage. When the voltage on the start battery exceeds 26.8 volts, the relay engages, combining the start batteries and the lithium batteries. It also has various time delays on engaging for various voltage ranges. This allows the start batteries to replinish before they feed the lithium bank.

In practice, I'm not 100% sure how well the setup is working. Here's the cycle I'm seeing with the bus running and shore power disconnected:

* Inverter on and under load (heat gun and shop vac), I can see the amp draw from the batteries for 4-5 seconds
* At around the 5-6 second mark, I see a current inrush (about 120 amps) and a voltage spike (30V) for less than a second and I hear the engine bog slightly
* Repeat ad infinitum

The state of charge was around 95% and falling slowly. It seems to indicate that alternator is not engaging for long enough periods of time to recharge the lithiums. I expected that the alternator would continue to run (engine bog slightly) continuously until the lithiums no longer accepted charge.

Maybe this is all normal. I need to run the lithiums down to a lower SOC and try again to see if the cycle changes.

In the meantime, does anyone have any feedback on what I'm observing?

[buswarrior]

What is the recommended voltage for charging the lithium batteries?

I am not sure that a straight combining will be good for them?

Also whether the simple voltage regulator in the coach charging system is competent to be charging lithiums?

I have only read enough about lithiums to know that that i need to read more.

Don't accidentally murder some part of your systems!!!

Happy coaching!
Buswarrior

[mqbus767]

Battle Born (makers of my batteries) advised me on two different phone calls that it is an acceptable way to charge the batteries. They recommended this specific battery combiner and others have used the same technology on various vehicles with various alternators including many high-amp models.

Spec. charge voltage range for my batteries is 28.4V - 29.2V. The combiner, designed for this, has voltage protection. (disengages outside of safe parameters).

The voltage regulator on the alternator may be an issue, but it's been said that others using a 50DN have successfully charged their lithiums in the same manner. Understanding that my setup my be different in some regard, there may still be a variable I'm not accounting for. I do not like the spikes to 30V that I'm seeing and is why I'm still using it in a strictly test capacity at the moment. Hoping to get some more answers before I atttempt to run it for long periods of time.

This method of charging the batteries is critical to my air-con plan going down the road, so I need to have high confidence that it's not damaging the batteries or the alternator.

[luvrbus]

You are lucky in respect that your alternator is belt driven ,the gear driven 50D does not do good with spikes at all just buy extra belts   

[freds]

The Victron Cyrix-CT is very interesting and relatively inexpensively device for it functionality.

I wonder if there is someway to trigger it once the RPM is above 1000 RPM, so it only draws power when you are driving?

[mqbus767]

Sure. The voltage control line on it, when open, disengages the relay. So, in theory, I could add a relay to that line that only engages when the ECM shows > 1000 RPM or any other variable.

[fortyniner]

Im planning a similar setup with oil cooled 50DN feeding 560amp 24 lifepo bank.
.
I think Battleborn has an integrated BMS that protects the battery from overcharge/discharge but it also may not be able to handle the 50DN 200+ amp charge
rate.
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There are some interesting alternator regulators available that can taylor charge profile for lifepo and one does have a sort of current limit function available in the form of belt load limit. 
.
If you want some good info on lifepo check out diysolar.com forum.
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I wish there was a 24v version of this available:
https://www.victronenergy.com/battery-management-systems/battery-management-system-bms-12-200