Lithuim AND Lead acid in same bank?

[Pitchondesign]

This is an interesting idea, but has limitations, which Clark identifies and comments on. It goes as follows. When the bank dischrges, after many days without solar, voltage will drop as the lithium and lead discharge. Assume the voltage drops to 12.0v, which is about 10% for lithium and 50% for lead. Then, a charging source is applied to the combined bank. The lithium will charge quickly, and the lead slowly. The lithium will reach full charge, and the lead will still need more. As the charging of lead continues, the lithium becomes overcharged. Lithium batteries are intolerant of overcharging and will be damaged, how much is hard to determine. This is why lithium charge profiles call for no float voltage when the battery is fully charged.

Clark clearly understands this and says he disconnects the lithium and lead when deeply discharged, and reconnects when the full charge voltages are balanced between lead and lithium. He also understands that connecting the batteries when the voltages are different can be catastrophic as massive currents will flow, damaging wiring amonst other things.

So, it can work, but it needs to be monitored. Clark is willing to do this monitoring, understands the risks, and has determined it is right for his boat.

[Fendell]

Originally Posted by Isba

http://nordkyndesign.com/electrical-design-for-a-marine-lithium-battery-bank/
This is not rocket technic it is cheap and it works ith less electronic systems see this page for advanteges and disadvantages.

I think you missed the point of the video, its not to protect the charging sources against Lithuim battery disconnect as your article mentions, its to use all the good points of both battery types. Maybe watch the video for more info

Originally Posted by Pitchondesign

This is an interesting idea, but has limitations, which Clark identifies and comments on. It goes as follows. When the bank dischrges, after many days without solar, voltage will drop as the lithium and lead discharge. Assume the voltage drops to 12.0v, which is about 10% for lithium and 50% for lead. Then, a charging source is applied to the combined bank. The lithium will charge quickly, and the lead slowly. The lithium will reach full charge, and the lead will still need more. As the charging of lead continues, the lithium becomes overcharged. Lithium batteries are intolerant of overcharging and will be damaged, how much is hard to determine. This is why lithium charge profiles call for no float voltage when the battery is fully charged.

Clark clearly understands this and says he disconnects the lithium and lead when deeply discharged, and reconnects when the full charge voltages are balanced between lead and lithium. He also understands that connecting the batteries when the voltages are different can be catastrophic as massive currents will flow, damaging wiring amonst other things.

So, it can work, but it needs to be monitored. Clark is willing to do this monitoring, understands the risks, and has determined it is right for his boat.

I haven't had much hands on experience with LFP and BMS, can you rely on the BMS to disconnect LFP say when the on charge voltage gets to 14.0 V, which would then leave the charging source to continue charging the FLA?

Are the BMS robust enough to be used on a duty cycle like the? or are they more of an emergency system?

Going one step further I guess you could have a under/over voltage DC relay operating a dis-connector (like below, taken from the link previously posted) so as it only would connect when the sensing voltages where within tolerance. definitely moving away from KISS territory...

[Isba]

I see your point but a good BMS should to this job with parameters you can select in the program by yourself like disconnect at a special voltage.

[rgleason]

Please refer to this thread Discussion of ZwerfCat’s hybrid LI/FLA design
There are a number useful links to similar designs.

https://www.zwerfcat.nl/en/lithium-hybrid.html

Nordkyn Design's website

See Stan Honey's pdfs here

See Endless Summers pdfs here


Here is another post with some of these links

[RogerLloyd]

I have two “ordinary” lead acid 12V identical batteries (from memory about 110 Ah each). I believe that they are traction batteries, which I understand is a half-way house between deep-cycle and cranking-amp batteries (?). My yacht is 29’ LOA. I have no separate engine start battery. I run house services off one battery when the engine is not running, and reserve the other battery for engine starting only.

I start my 2 cylinder Bukh DV20 ME 0.964 litre diesel engine using both batteries (to minimise the load on each). In case the batteries should fail to start the engine because of a low state of charge I have purchased an (18000 mAH / 66.6 Wh, as stated in its instructions) lithium (the instructions do not mention the word lithium ?) jump-start battery, dbPower DJS50, apparently suitable for diesel engines up to 5.2 litres. Some of posts on CF seem to throw doubt about using a jump-start battery with lead-acid batteries.

I assume that to start the engine I would set the battery switch to "Both", connect the jump start battery in parallel (red to red first), press the go-button on the jump-start battery and then immediately start the engine. Then (whether the engine starts or not) I would immediately remove the jump-start battery (presumably black lead first).

In any case I believe that Ah * V = Wh. So 18000mA * 12 V => 18A * 12 V => 216 Wh, which is not 66.6 Wh, as stated in the instructions; so that confuses me.

The instructions say:-
DC input for charging: 15V. (So I assume that the jump start battery is nominally 12V ?)
Jump starter peak Output: 600A.
Starter Output: 300A.
But there is no mention of CCA; which I find confusing.

The instructions also say to discharge and recharge the battery at least once a month. However, I read elsewhere that LiPo batteries have no “memory”, and also that they do not like remaining for long periods of time either full charged nor at a low state of charge.

[I believe that my MacBook Pro also has a lithium battery. I was advised to discharge that once a month, keep it discharged overnight, and then recharge it fully. So Apple seems to agree with dbPower. My computer spends most of its life attached to a mains power supply. If what I read about lithium batteries is true then Apple should keep the battery at 50% charge for office use and only allow a charge to 100% when a lack of mains power is expected by the owner. However Apple does not offer that possibility.]

I also read that there is a problem when connecting a fully-charged lithium battery across a discharged lead battery, because the lithium will provide a high charging current, which will heat the connecting wires and also ruin the lithium battery, because lithium does not like providing a high current load. Well, surely this is what is required of a jump-start battery ? So again I am confused !

I would be most grateful for expert thoughts.

[CarlF]

This is interesting.

But since we have such an experienced group here, I have been musing about the best way to protect the alternators should the lithium bank I want to install go offline. I'll be using drop-ins that don't communicate.

a) Install a Sterling "alternator protector"

b) Count on a Victron 30amp dc-dc charger to the AGM start bank to buffer a surge.

c) Install a small/inexpensive lead acid battery in parallel just for surge protection - would even a little 20AH wheelchair battery be big enough to handle the brief surge? I figure this will be so small that it will never cause overcharging.

Or do all three of the above? Doesn't cost much.

[SYCavalier]

Originally Posted by Fendell

Trawling YT last night and came across an interesting Vid that I would like to put to the brains trust, has this been discussed yet? sorry if so.

The fella makes good points about the way his hybrid system works, and in theory it should work well as long as all the parameters he speaks about are met. With modern systems and the monitoring available would this be enough to stop any damage with mixing chemistry?

I will say though, from an engineering point of view any one trying this needs to heed the warning about making sure the voltages are the same before linking the two batteries, as that could get very ugly...

Thoughts?

Only watched to about 3 minutes.

My thoughts:

Lead has no advantages over Lithium.

Lead is not cheaper than Lithium, though this is a common misconception.

When comparing the two, compare cost per amp of available capacity rather than cost per battery.

A 100AH Lithium battery deliver the same available capacity as a 200AH lead acid. If you then factor in the 2,000 to 3,000 cycles of Lithium to the 500 cycles of a good quality lead acid, then you'll see Lithium is in fact cheaper.

Lead is more than three times the weight of Lithium. As an example, I replaced 440 amps of lead with 400 amps of Lithium. This doubled my available capacity and reduced the weight by about 50%

Charging:

You can discharge your lead acid battery to 50%, you can get back to 85% reasonably quickly but the remaining 15% takes time. The result is that your lead acid batteries give you between 35% - 45% of their stated capacity available for use.

You can safely discharge Lithium batteries to 10% while maintaining steady voltage throughout, meaning you have available capacity of 90%.

Lithium typically accepts charge at 0.5 - 1C meaning, assuming you have the charging capacity, a fully discharged battery can be fully charged in 1 - 2 hours.

There are specific and very different settings on smart mains powered chargers, engine driven alternator controllers and solar controllers for Lithium and Lead.

As for mixing the two; NO, THE TWO SHOULD NEVER BE MIXED.

[T1 Terry]

Haven't posted over here for a while, it started to get like the old days on other threads and I decided I had better things to do than go into that hole again.

Quality lithium batteries can deliver 100% of the advertised capacity with harm, but that is not down to zero volts, two different things. If the battery is 100Ah and a good quality battery, it can deliver 50 amps for two hrs (C2) or 100 amps for 1 hr (C1), using the old lead acid battery C20 rate or discharged at a steady 5 amps, a lit more than 100Ah would be available, but calculating just how much more would be a headache, so using a quality BMV like the Victron 712, you can see just how much you have used so you know what is remaining before you have used the 100% of the advertised capacity. I guess if you were the dare devil type, you could use the end of discharge when any cell hits 2.8v, but does anyone need to cut it that fine?

Basically, you can use any type of charger you want, but you must be able to stop the charging if a cell reaches 3.6v and not resume the charging until the high cell has dropped below 3.6v ..... sense says you would want to put a bit of a gap between stop charging and restarting charging, the easiest method is a timer set to stop the charging from 1 min up to 1hr if you feel the need, AFTER the high cell drops below 3.6v. The high cell alarm should auto reset once the high cell has cleared so it can do the same thing again if a cell goes over 3.6v.
For this reason, the simplest way to avoid damaging the charging equipment is to parallel charge a lead acid battery with the lithium battery, that way when the lithium battery charge cut kicks in (if a cell reached 3.6v) there is still a path for the charging current to flow .... into the lead acid battery.

That is the only linking between lead acid batteries and lithium batteries you would normally use, but maybe a battery switch to link the lithium battery to the leadacid start battery if the start battery no longer had enough grunt to spin the motor over .... but with a big red light to show the two batteries are linked so you don't forget :lol:

We now have a number of battery packs over 10 yrs old and still going strong, so the 10 yr life nonsense has been debunked, and we recently found a Sinopoly 100Ah cell that was part of a batch lot I bought from an abandoned EV project. The majority of the cells are still working as a house battery, but this one cell ended up in a packed in box when we moved inter state. Tracing back the cell is over 11yrs old since manufacture, it still reads 3.388v at the terminals, so the nonsense about them self discharging over the yrs is also debunked .... what other myths are still to be debunked?

T1 Terry

[SYCavalier]

This may be worth reading;

https://offroadliving.com.au/blogs/1...d-acid-charger

[rgleason]

I found the link below useful to explain why you need LFP specific chargers that kick in at 13.1-13.2vdc rather than FLA chargers that kick in at 12.5-12.7vdc to start charging. This affects the depth of cycle and drawdown of the LFP to 25% and the efficiency of solar trying to charge.
Additionally FLA charger trickle charge mode is deadly to LFP!

Also Jason points out that Solar PV requires dedicated LFP controllers, and DCDC should also be setup for LFP if those are used.

Also, keep in mind that internally the LFP is made of cells that cannot be overcharged or depleted, and that these cells can act differently if you don't have a "matched" set of cells or if one of the cells has been slightly damaged. The purpose of the BMS is to protect the cells and to balence them either by top balancing or bottom balancing. In order to have the cells fully balance, occasionally the battery needs to be charged more fully (top balancing) for the BMS to do its job, or each cell needs to be hand balanced and checked occasionally (about 1 month-3 months depending on the set of cells) if there is no BMS.

Being realistic about my habits I would prefer not to have to do this manually, thus a BMS would be good for me. Also I would like to have the battery protection that a BMS provides by disconnecting on high SOC, overvoltage, overtemp, undervoltage, low SOC, low temp, etc

However some passionate users are able to keep tabs on their LFP and manage them without BMS.

[rgleason]

Here is an interesting DC DC LFP Battery charger 12vdc/24vdc 40a output that is waterproof and accepts and manages power from Solar and Alternator . Good for LFP to 200ah.
https://offroadliving.com.au/product...-charger-solar

[WhiteHill]

Five months later, came across this:

https://www.youtube.com/watch?v=wjFl78CorZ8

https://www.bos-ag.com/products/le300/

[Saltyhog]

I saw that RAN sailing on YT is installing an LFP bank. He’s using a BMS from https://batterybalance.com/x2-bms-12-24/. It’s a hybrid lead/lfp setup with separate load and charge buses. Looks really interesting.