New lithium questions: generator starting and charging

[neoflyer]

I’m getting closer to installing my LiFePO batteries. I just read something I hadn’t thought of before. Actually, in a way the subject did come up. Previously, the issue arose that lithium house batteries may not be very useful to help the chassis batteries if they are too low to start the engine.
Now an added issue. I only recently found out my generator uses the house batteries to start. It was pointed out in an article I read that lithium batteries don’t have the current capacity needed to start a diesel generator. I do know that I usually have to crank the generator starter for some time when it is cold. Is this going to be a problem?
Question two. I was planning to add a DCDC charger to effectively use the engine alternator to charge the lithium house batteries. Now I learn about a product called a battery combiner that will need to be upgraded. I have no idea what one of those is. I read the description but remain confused. Is it the same as my Trombetta relay? Does it replace it? I know the two voltages of the different battery banks are compared to tell the system when to charge the house batteries when the alternator is charging? Can someone educate me on this?
Ed
’05 HR Ambassador Diesel motorhome

From amsolar.com:
2. Alternator Charging: When upgrading to lithium batteries you will need to upgrade your battery combiner for alternator charging. Without this modification, the higher resting voltage of a lithium battery will trick the existing battery combiner relay into thinking the alternator is running and the lithium battery bank will be paralleled to the starter battery, even when the ignition is turned off. The result is lithium batteries draining into the starter battery until they crash to a dangerously low voltage or the lithium batteries’ internal BMS engages, preventing further discharge.
If you have a lithium battery system that can handle a charging current of 150A or more (three or more Battle Born lithium batteries), and you do not have a smart alternator (here’s the Smart Alternator Test) you use the Victron Cyrix-Li-Ct battery combiner, variant “Lithium / 230A”.

The Victron Cyrix-Li-Ct can quickly charge a lithium battery up to about 80% state of charge.

If you have a smaller battery bank (one or two Battle Born batteries) and/or a smart alternator, you will need to use the Sterling Battery to Battery Charger. The Sterling is programmable for any battery chemistry and can bring a battery up to 100% state of charge.

Neither device is needed if you plan on using AGM batteries.
Estimated Installation Labor
High Current Alternator Charging
3 hours / $435


Victron Cyrix Battery Combiner
from 40.00
Victron Cyrix battery combiners connect your house battery bank to your starter battery and alternator to allow alternator charging. Additionally, when a charge is applied to a house battery bank the Cyrix will close and allow current to flow to the starter battery. Select an appropriate Cyrix based on your house battery type and alternator current rating.

Alternator 160A or less - 120A Cyrix
Alternator more than 160A - 230A Cyrix
Battery Type / Rating:
Select Battery Type / Rating AGM / 120AAGM / 230ALithium / 120ALithium / 230A
Quantity:
ADD TO CART


Sterling Battery to Battery Charger 12V/60A
425.00
This device is ideal for lithium alternator charger system upgrades in motorhomes where a smart alternator is used, or when the lithium battery bank cannot handle high current.

 

[Rocketman]

The lithium batteries themselves may have enough power to start your generator/chassis motor... But what bms are you using and what is the ah of the bms??? (That is often the limiting factor).

I am adding lithium’s this spring to my diesel MotorHome and have the same issues you have.

I will be installing 8 lishen 270ah cells into one 12v 2p4s battery (useful 500ah). I am using Batrium’s watchmon4 bms with a Tyco contractor EV200AAANA. This way the full amperage of the batteries are available to boost the chassis motor. My diesel manual wants a CCA battery (cold cranking amps) of 1100. That is just over a 2C discharge for 6-ish seconds (without help from the chassis battery) so I think I will be fine.

There are several ways to prevent alternator charging issues with a lead chassis and lithium house batteries. My choice is to break the charging connection between the alternator and the house battery. I think I will have enough solar to not need a dc-dc charger - such as the sterling one you referenced. (But I can always add it later if I feel like I want/need it).

Because I will not be charging with the alternator I don’t need any kind of combiner - which is what the Victron Citrix is. I figure if my solar is not enough then I will run the generator for an hour or so - I probably will not be running it much...

These are all issues we all have when adding lithium’s for house batteries. There are several different ways to make it work - you just need to find one that works for you and your rig.

 

[Rocketman]

I just went out and found that you will be using 5 12v batteries. For the batteries you are getting what are the discharge specs - both continually and surge?

Also how many amps does your generator require to start? And you big diesel?

 

[neoflyer]

I will start with 4 Lion Energy UT 1300s. From their website: “It can do 900A for a millisecond (a spike) then approximately 250A for one minute and 150A continuous (how much power it puts out) capacity”.

On a similar note to starting the generator I have a Trombetta relay that regulates alternator charging of the house batteries. It also has a switch at the driver position to close the relay so the house batteries can help the chassis batteries start the engine if they are low. On one thread it was advised, if the house batteries are lithium, to operate the switch for several seconds before engaging the starter to allow the house batteries to charge the chassis ones a little. That would reduce the demand on the house batteries. I don’t know how well that would work.

Assuming I install solar at the same time as the batteries I think I’ll initially install them without alternator charging. If they have difficulty starting the generator I might be able to rewire the chassis batteries to start the generator.

 

[neoflyer]

I’m checking the the generator starting amperage. Will update when I get the information.

 

[Rocketman]

I don’t think you will have any trouble starting your generator, and I doubt you will have problems boosting the big Diesel.

You will have one minute for your generator to start. Four batteries at 250amps is 1000 amps of starting/boosting power. My Cummins ISC Diesel wants a battery with 1100 CCA (cold cranking amps). The generator uses a lot less.

The issues may be your wiring - are you using the same gauge? (in my case 4/0). Fuses - a 400 amp class T fuse will probably pop if you put 1000 amps through it. And changes you make to your Trombetta relay to prevent alternator charging.

You need to think through each area of your system.

 

[neoflyer]

Thanks Rocketman. You read between the lines and deduced what I shoulfpd have said, the batteries will be in parallel.

I have 2/0 wiring from the factory, which has been sufficient, although I have never touched for temperature after generator start. Your point about fuses is well taken. This is an area I need to educate myself on.

 

[jwelter99]

I put a selector switch to the generator starter to allow me to select the starter or house batteries as the source.

This way if lithium house batteries are critical low the generator can still be started off the starter battery and used to charge the lithium. If the starter battery is low the generator can be started off the lithium to re-charge the starter battery. If both are dead I wait for the sun to shine

Genset takes a peak of 150A to start and my 840Ah 12V pack has no problem supplying this.

For question #2 I would go direct to a B2B charger. I use a Sterling 120A and it works great. I have 270A alternator and get full 120A charging. BBW12120 is the model I use.

 

[Hedges]

How about wiring the starter to bypass BMS, but have BMS control starter solenoid?
Cranking current will come straight from the lithium cells, but if voltage drops too low, starting solenoid disconnects.

Alternatively, with a suitable gizmo you should be able to recharge an AGM starting battery from lithium. Just have to be more patient.