Inverter to lithium question

[Stu Jackson]

Originally Posted by freshalaska

I have an old Xantrax inverter that will charge at 100 amps but is not compatible for chargeing lithium batteries. Can I have the inverter go thru a Victron 100 amp programmable solar controller so I can program the charging profile? Or what other way to do it? New charger is close to $900.
What do you think.

Is it a Freedom 20? I have a Freedom 15 which charges to 75A, 1500W inverter, whereas yours is 2000W inverter.

If yours goes back as far as dipswitches, it may be older than my 1999 model, although IIRC you are right: there were only two settings, most likely wet & gel because AGM had not been invented yet.

This may help on the manual:

DISCONTINUED XANTREX PRODUCTS LINK

http://www.xantrex.com/power-product...-chargers.aspx


Your "through the solar controller" and your "inverter/charger/inverter/charger" ideas are suspect at best, dangerous at worst, and unnecessary.

I do not have lithium batteries, but I have read a great deal about them, both here and on trusted Rod Collins' website www.marinehowto.com

There is nothing magic about charging voltages other than don't go higher than manufacturer's recommendations. I think we all know by now that gel require a lower voltage than wet cells, it's only been 30 years so maybe everybody finally has read the memo!

Having done my own extensive reading, and having read most all of the lithium and pre-lithium subforum posts in the electrical forum here, I believe sailorboy1 is correct.

It's what I would do with my Freedom 15 combined inverter charger. If indeed my guess is what you have is correct, you don't have a choice if you want to use your current equipment.

You don't know me from Adam but I have been active on this and sbo and administer the Catalina 34 website. I have owned my boat for 25 years. Boat electrical systems interested me so much because in 1998 when I bought my then 12 year old boat it had two banks but only one alternator and "the thing" back then was chargers with dual outputs. I had to learn quickly because I wanted to anchor out while my PO was happy tied to the dock. I learned about combiners and a lot more and assembled my input here for others to use: Electrical Systems 101 http://c34.org/bbs/index.php/topic,5977.0.html

That said, for battery charging there are only two things that are important/critical:

1. do not exceed manufacturers' voltage limits for charging

2. it doesn't hurt to go below those voltages because all it means is it will take longer to charge (with any voltage higher than 12.8V)

LiFePO4 has a further limit on the knees at the end which you should be aware of.

I urge you to read sailorboy1's material, he makes valid, useful points right up your alley. jedi is another trusted contributor.

Then make up your own mind. Your boat, your choice. If I was buying lithium and wanted to keep my Freedom 15, I'd keep it and start at least by using the gel settings (since I have the manual but not in front of me, I'd check the voltages, even the wet cell settings might be fine because float is 13.2 or 13.4, bulk is 14.4). With lithium you WILL NEED to deal with MANUALLY managing the duration of the various phases of charging. This alone may be a deal breaker for you.

Good luck, happy research.

[rwidman]

You will probably have to keep an AGM or flooded cell battery for engine starting so you can just connect your engine alternator and your shore power charger to that battery and use a DC to DC charger made for the purpose to provide the correct charging parameters to your lithium batteries.

Several of the lithium battery makers sell these chargers.

[freshalaska]

My inverter charger will put out 100 amps continues duty cycle. I think 100 amps a little over kill for just one starter battery. Why waste 100 amps and why not put those into the house bank as it’s muck larger capacity than the start battery and does get drained down and takes longer to charge. In fact I have isolated start battery that I never use I alway use the house bank to start the engine. It’s just a back up that to date I’ve never had to use. The alternator alone will charge the start battery and probably in just a few minutes time. Pretty much everything runs off the house bank. Do other people run loads off the start battery other than to start the engine. To me it makes more sense to run lights watermaker etc off the house. The start is designed for a big dump of power in a hurry. House is different story more of a prolonged load over time.

[freshalaska]

Giving its little more thought dc2 dc charger might get the job done seems the inverter charger is on a time limit for bulk and way to short a time for the lithium’s if the bank is low. Not real sure how that inverter charger would Handle that.

[wholybee]

Originally Posted by sailorboy1

Just why in you world is charging the batteries in spec going to shorten the battery life?

It is not the voltages, but the time spent there. Normally to charge an AGM, you bulk charge until the voltage is reached (14.1V) and that is fine for LFP. But for AGM, once you reach 14.1, you hold that in an absorption mode until tail current drops to some preset level. For LFP, you should immediately drop to the float voltage. It's that extra time holding 14.1 that is considered bad.

So while the voltages might be "in spec" how do you know that the termination parameters are?

How much that extra absorption time affects LFP is a different matter and a different argument.

[aberglas]

My understanding is that most Lithium batteries come with complex controllers, unlike AGMs. So that the voltage that you apply to them may have little to do with what actually goes into the cells.


No?

[sailorboy1]

Who has a charger that measures tail current?

Out are just timer

Btw specs on charging my LFP batteries say 14.4v and 2 amps (2%)

[sailorboy1]

I have had enough to with topic and am going to ignore this thread so battle with someone else

[plittle2005]

An interesting and definitive article on this subject: https://glider-battery.eu/post4-1/

[MVDarlin]

Bottom line, the AGM setting will work but just not fill the last little bit of potential charge you will get with a higher LITHIUM setting of 14.6. If you are using solar panels with a smart controller set for lithium it can make up the difference. You still get the benefit of most of the charge potential.

[wholybee]

Originally Posted by aberglas

My understanding is that most Lithium batteries come with complex controllers, unlike AGMs. So that the voltage that you apply to them may have little to do with what actually goes into the cells.


No?

The "complex controllers" are very simple, and have nothing to do with charge voltages. The BMS simply disconnects the battery if any of the cells are individually overcharged or over discharged. Lead Acid can be repeatedly overcharged without much damage. An equalization charge is just overcharging and is considered GOOD for lead acid. Overcharge an LFP, and it is significantly damaged the first time it happens. So, a BMS is added to prevent that.

Another difference is that LFP have little to no self discharge. An AGM needs to "Float" or "Trickle" charge to keep it at 100%. That low current charge can overcharge an LFP, so you want to avoid it. This means avoiding "3 stage" chargers for one that instead has only one stage, charging and not charging.

Lastly, the voltage issue you are referring to is that LFP has a very flat voltage. That means that while with Lead Acid the voltage goes up as it charges, with LFP the voltage stays the same until it is fully charged, and only then does it rise quickly. So the way you might be used to knowing of your battery is charged, by looking at the voltage, won't work. The voltage has very little to do with the current state of charge. It could be very empty or vary full, and still have the same voltage. You need a more sophisticated meter.

[freshalaska]

Thank you Warren. I’d like to do a proper job and my inverter/charger won’t cut it for me. Maybe would work fine for others but not for me.