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Lithium battery upgrades

January 04, 2021, 11:12:44 am

 I am in the process of acquiring all the items to change my house batteries out to Lithium. I currently am running two 8D house batteries ( liquid acid batteries ) which only give about 152 usable amp/hrs., weigh a ton, and require constant maintenance and observation to keep from over or undercharging batteries. Yes we all know the initial cost of lithium, but the introduction of the BMS to the system will be a HUGE advantage of not having to worry constantly about the batteries. The good side, the inverter/charger has a charge profile that so closely resembles what is needed on the lithium that I will be able to utilize it for now. The bad side, since my alternator charges both the house and chassis batteries, I need to be able to intercept the house side of this charging circuit, thus eliminating these two battery systems from "seeing" each other through the alternator charging circuit. I'm not to worried about the battery boost switch, as I control that operation with a manual switch. I want to intercept the circuit that charges the house batteries, so I can install a DC to DC charger there to handle charging off the alternator while engine is running. Does anyone have any knowledge of this system and how to intercept? Thank to all for the input.

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Re: Lithium battery upgrades

Reply #1 – January 05, 2021, 01:33:21 pm

Hi AJ
As you know, your Battery Boost Switch controls a solenoid that combines the two batteries.  But when the engine is running that solenoid is actuated automatically, regardless of the ‘Boost’ switch setting.  If you must separate the charging circuits, this is where I would start.  You may be able to reconfigure the wiring to control the solenoid with the boost switch only.
I did not do that, but then, I have LiFePo starting battery also.  I could do that because I have no BMS at all. 
I have an old Heart inverter/charger, for wet and gel only, and use one of the 4 charge parameters available, it’s not perfect but it seems to be fine.  I did install a Balmar alternator regulator that is fully programmable and has temperature sensors.  I also put a switch on the echo charger, leave it off mostly. 
Ed 2000 Magna 5738

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Reply #2 – January 05, 2021, 03:04:53 pm

Good idea sir. I did not know I could use a lithium battery for starter motor. That would sure simplify things so as not to have two battery types.I guess it's the BMS that limits being unable to use lithium for starter motor due to high current draw from starter? With no BMS you are able to draw as many amps as the starter wants as long as voltage stays usable?

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Reply #3 – January 05, 2021, 10:28:50 pm

Yep, I think the BMS is the limiting factor.  I assembled my batteries out of a bunch of single cells that are each 100a and 3.4v each.  They are 8p – 4s for the house, 800ah, and 4p – 4s for the chassis that’s 400ah, both are 13.6v.  Neither battery looks anything like what you would see in a truck.  The starter works great because voltage is right up there, even at the lower end of the capacity.  Now, there is no low voltage safety cut off or automatic balancing, but I check the balance once a year and I did do a manual balance last year.  So one time in 6 years.
Ed

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Reply #4 – January 06, 2021, 10:19:24 am

This sounds like it would be a much more viable option. Probably way more cost effective in the end, than running two separate types of batteries. The alternator upgrade would probably equal out in cost, due to not having to buy the DC to DC charger and the significant cost savings of building my own battery for the coach from scratch. Now....just to study up on that so as not to get in over my head.
 Thank you so much for all the info. Definitely a learning experience. If your ever in SE TX reach out please sir.

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Reply #5 – January 07, 2021, 01:33:01 am

If you have any questions, I would do my best to help.  Good luck.  Ed

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Reply #6 – January 13, 2021, 08:21:07 pm

Hi AJ,
I saw this on you tube and thought of you.  This guy tells how to connect Li batteries and Lead.  I found it very interesting.
https://www.youtube.com/watch?v=tAuPfgZgXec
Ed

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Reply #7 – February 02, 2021, 01:38:18 pm

That was absolutely enlightening. That was a ton of information that most lithium "users" would say is crazy. BUT IT MAKES SENSE!!!....I took your advice and have ordered the cells and BMS to build ( starting with ) 600aH of lithium batteries for the house bank. The cost was so substantially lower ( almost by half ) that I now have the budget left over to double my original thought of capacity. So going to build a 1200aH bank. Still going to keep my starter battery isolated and use a DC to DC charger for the lithium. Thanks so much for the link.

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Reply #8 – July 12, 2021, 03:26:45 pm

Ed,
I have a 2007 Magna 42' all electric coach.
I have a few questions, I too just upgraded my 6x8D AGM batteries to 3x300AH Ampere Time Lithium batteries.  I have 2 Freedom SW 3012 inverters for charging and power needs.  The Xantrex has a custom setting for a 2 stage 14.4V Bulk and Absorb charge profile.  Float turned off. 
1.  If I charge the lithium with the alternator while driving, will that be bad for the batteries or the alternator? I have a 340 amp alternator and 2x8D lead acid batteries for starting.
2.  If I install a DC to DC charger for travel, how do I wire it in to the existing configuration?  I have a Magnum battery combiner installed and a 300amp seloniod, for connecting the 2 battery banks.
3.  How will the new charge profile for my lithium effect my coach batteries when plugged in? No Float
4.  If you start out each trip with fully charged house batteries (lithium) would this negate the need for a DC to DC charger?

Thanks
Steve

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Reply #9 – July 13, 2021, 01:21:01 am

Hi Steve,
Congratulations on your new battery purchase. 
I’m not sure I can be much help.  My knowledge is limited to my experience with what I have and my battery is totally different.  I can tell you what I have and what I do.  I don’t have a dc to dc charger and I don’t have a BMS, and I don’t have lead acid batteries at all.  I do have LiFePo batteries but my system is different than what most are doing.  You are using Lead acid to start and your LiFePo batteries are in a standard battery shape, no doubt with integrated BMS.  My batteries are single cell and not in a standard configuration.  With no BMS I can use LiFePo for starting, so I’m not combining with lead acid. 
I made no modifications to the charging systems at all for the first 4 years.  I still run a 22 year old Heart Freedom 25 inverter charger, the Echo charger and all.  It has no Li settings but has 4 LA settings.  I choose charger settings with battery longevity in mind rather than worrying about full charge, but I do not have an all electric coach.  However I do charge the batteries fully to 14.4v before starting on a trip, no reason to charge the thing with the alternator.
I ran my 160 amp alternator with no mods for years with no problems.  The alternator thinks that it is charging Lead Acid batteries and the voltages are controlling the charge rate; the voltage of my battery at 10% charge is close to the voltage of a lead acid battery at 90% charge.  So the alternator will not try to pump out 160 amps, even though there is room in the battery for it.  That’s my belief and I’m sticking to it!  My experience seems to bear this out.  After 4 years, I installed a Balmar charge controller on the alternator that is fully programmable with high temp cut off with sensors on the alternator and the battery.  Again, my system is simple because I have no LA.
I do not have a BMS at all, nothing, no balancing, no high amp cutoff, no low voltage cutoff.  I have to be vigilant about charge levels and I check the balance once a year.  I have only had to rebalance once in 6 years.
I think that a lead acid charge profile would be better for a LiFePo battery than a Li profile would be for a Lead battery.  The LA battery needs to be fully charged for the health of the battery and it needs the float too.  If I were trying to charge both I would look at the possibility having them combined all the time, rather than combining them at different voltages.
Again, I have no experience with the battery system you have so I’m not much help.
Ed

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