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rvrrat · 03-17-2025, 12:05 PM

Hoping all of the smart people on this forum can help educate me on this question.

We just upgraded our 2017 Phaeton 44OH from AGM to Lithium house batteries. We installed 2 Vatrer 460ah batteries and based on this groups great advice, we have the magnum remote setup with the proper setting, etc. Everything is working great and it has been a true game changer.

We currently rely on Solar, Generator or 50Amp Plug in to charge the battery bank. The one downside with the Lithium batteries that has been discussed here before is that the voltage does not drop enough for the Spyder merger algorithm to connect the house and chassis batteries while driving - so the alternator is not charging the house batteries. Using the dash mounted button, I can manually connect the batteries and observe, when the engine is running, that there are 60 amps going into the house batteries....perfect.

In these forums, people recommend installing a DC-DC charger - but isn't that the same thing as we already have when the Spyder systems mergers the batteries together - or am I missing something on this?

My thought was that I could replace the spring loaded dash button with a true on/off switch to connect the batteries while driving (if needed) and turn off when the batteries were charged. I am trying to understand the downside of doing this other then having to monitor it and turn it on and off.

Has anyone spoken to the team at Spyder to see if the merge algorithm could be reprogramed to account for the higher voltage of the Lithium batteries? That of course could be the perfect solution.

Any thoughts? Thank you in advance for helping to educate me.

Safe Travels and enjoy the adventures.

d23haynes57 · 03-17-2025, 12:21 PM

For the merging of the chassis to house batteries for alternator charging, why would the system look for a lower voltage on the house bank? How is the connect-disconnect voltage set? Can you adjust it? Maybe the disconnect voltage is set too high. Set connect if either bank is at 13.6 and disconnect at 13. Yes, they this will leave the banks connected after charging stops for a while. There is some benefit to this. The Lithium battery voltage will drop as SOC drops especially with a large load.

rvrrat · 03-17-2025, 12:43 PM

Unfortunately the merge algorithm is not adjustable - that I am aware of.

Based on the current specs, when the engine is running and the house batteries drop to 12.4 volts, the Spyder system connects the house and chassis batteries for 1 hour. These settings work great for Lead acid or AGM batteries, but not for Lithium.

d23haynes57 · 03-17-2025, 12:51 PM

Quote:

Originally Posted by rvrrat

Unfortunately the merge algorithm is not adjustable - that I am aware of.

Based on the current specs, when the engine is running and the house batteries drop to 12.4 volts, the Spyder system connects the house and chassis batteries for 1 hour. These settings work great for Lead acid or AGM batteries, but not for Lithium.

Sometimes I am very happy I don't have much intertwined and restricted stuff on my 2008. Why, even with Lead acid or AGM would I not want to connect the alternator to charge the house batteries until they are discharged? Why wait to the point that when we connect, we smack the alternator with that load instead of topping them off.
Someone at Spyder should be able to make a program modification. Give that a try.
If not consider your own combiner. This is my go-to.

https://www.bluesea.com/products/762..._-_12V_DC_500A

twinboat · 03-17-2025, 02:54 PM

A DC-DC charger boosts the voltage to lithium values for full charge. Your alternator will not do that thru the merge solenoid.

d23haynes57 · 03-17-2025, 03:00 PM

Quote:

Originally Posted by twinboat

A DC-DC charger boosts the voltage to lithium values for full charge. Your alternator will not do that thru the merge solenoid.

Straight on alternator-diode block has no problem bringing my 3, 300 A/H batteries to full charge and having the internal BMS turn charging off. Just takes a little bit longer than the 150 amp charger. No need to get batteries to 100% off the alternator or daily either. That can occasionally be done when you plug in to power.

rvrrat · 03-17-2025, 03:02 PM

Quote:

Originally Posted by twinboat

A DC-DC charger boosts the voltage to lithium values for full charge. Your alternator will not do that thru the merge solenoid.

@Twinboat - thank you for your response. I appreciate it. Do you know what the limitation is on the merge solenoid. I see 60 amps being produced so that's good but wondering, based on your statement, if there is a cutoff built into the merge algorithm.

Thanks again.

d23haynes57 · 03-17-2025, 03:13 PM

Quote:

Originally Posted by rvrrat

@Twinboat - thank you for your response. I appreciate it. Do you know what the limitation is on the merge solenoid. I see 60 amps being produced so that's good but wondering, based on your statement, if there is a cutoff built into the merge algorithm.

Thanks again.

Depending on alternator size and wiring there may be current limiting in the coach design.
As the Lithium batteries reach full charger the voltage increases and get close to the output of the alternator so the charging rate will decrease especially as you get near 80% and higher. This is why some say you need the DC-DC which can step up the voltage. They also draw more current to do that. a 40 amp DC-DC will pull more than 40 amps as the alternator voltage drops. Actually, making a marginal alternator system worse.
Get your batteries down to about 20% and then test the alternator charging rate. What is your charging rate using the inverter/charger?

twinboat · 03-17-2025, 04:05 PM

The merge solenoid doubles as the boost start solenoid, so it can handle more then a few hundred amps for a short period and about 200 amps steady.

bentjm · 03-18-2025, 07:10 AM

Very interesting thread. I have talked to many people about using LifePo as house batteries.

I have two concerns:

1. Potentially damaging the alternator. The built in limitations of the existing wiring and now this information concerning the Spyder programming seems to alleviate that concern. Of course, it adds a concern that the house batteries won't be charged driving down the road without a DC to DC charger.

2. Starting the generator using LifePo batteries. The specs on my QD1000 says 600a to start. The overcurrent draw protection in some BMS could keep the generator from starting.

shepardmike · 03-18-2025, 07:15 AM

Quote:

Originally Posted by bentjm

2. Starting the generator using LifePo batteries. The specs on my QD1000 says 600a to start. The overcurrent draw protection in some BMS could keep the generator from starting.

I have had no issues starting my 10K gen with my LifePo's

Tony Ramirez · 03-18-2025, 07:18 AM

I have 2 batts w 200Amp Max discharge, so 400Amp total. Starting my 10K Onan has not been am issue, even w temps in the low-mid 20s.

d23haynes57 · 03-18-2025, 07:33 AM

Quote:

Originally Posted by bentjm

Very interesting thread. I have talked to many people about using LifePo as house batteries.

I have two concerns:

1. Potentially damaging the alternator. The built in limitations of the existing wiring and now this information concerning the Spyder programming seems to alleviate that concern. Of course, it adds a concern that the house batteries won't be charged driving down the road without a DC to DC charger.

2. Starting the generator using LifePo batteries. The specs on my QD1000 says 600a to start. The overcurrent draw protection in some BMS could keep the generator from starting.

Current observation with the QD 12.5K is ~ 265 amps to get it going. Original Lithium upgrade was 2, 300 A/H batteries with 200-amp BMS each. Starts the generator with a vigor far superior the 3, 200 A/H Lifeline AGMs that were in there. I added a 3rd battery for capacity. Using the boost to help start the engine even with healthy chassis batteries I see a 300 amp assist while cranking. BTW, a 3000-watt inverter needs 300 amps or more. If you can support that continuous load no problem starting the QD. With the 3-battery set up now I can run the microwave and start the generator at the same time. Did it as a test.

bentjm · 03-18-2025, 08:16 AM

Quote:

Originally Posted by d23haynes57

Current observation with the QD 12.5K is ~ 265 amps to get it going. Original Lithium upgrade was 2, 300 A/H batteries with 200-amp BMS each. Starts the generator with a vigor far superior the 3, 200 A/H Lifeline AGMs that were in there. I added a 3rd battery for capacity. Using the boost to help start the engine even with healthy chassis batteries I see a 300 amp assist while cranking. BTW, a 3000-watt inverter needs 300 amps or more. If you can support that continuous load no problem starting the QD. With the 3-battery set up now I can run the microwave and start the generator at the same time. Did it as a test.

Yeah. I have been getting somewhat in the weeds.

Some 280ah batteries have BMSs with some really tight overcurrent settings - 220 amps for 1 second. Some have no overcurrent at all - will pull 600a.

I have 6 6v FLA currently. They are in good shape, but my 2022 Allegro Bus 40IP pulls a lot of power when off grid. I can't go 24 hours with the current setup. Just looking for something that will make the few times a year we go off grid a bit simpler.

I am looking at 3 280 ah LifePo batteries. Not sure if my use case really requires a DC to DC charger or not.