diy solar

diy solar

This guy thinks outside the box adding lead to a LiFePO bank...

Ceberha said:
In some of the earlier thread more senior/experienced folks had raised concerns about large currents such as this and the need to match voltages before putting the LFP and lead acid packs in parallel. At a minimum you would need to make sure that your BMS and wiring could handle it...
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Yes, absolutely. The person in this video also addresses that hazard also and recommended wiring a a resistor to balance the LA and Lithium batteries before connecting them directly.
 
One of the main advantages of LiFePO4 is not outgassing. The failure state of an older AGM battery is outgassing hydrogen (I had a 220Ah 48V bank fail and started outgassing). That alone would prevent me from wanting to mix the two.
 
rhino said:
One of the main advantages of LiFePO4 is not outgassing. The failure state of an older AGM battery is outgassing hydrogen (I had a 220Ah 48V bank fail and started outgassing). That alone would prevent me from wanting to mix the two.
Click to expand...

Did your nose alert you?

I left a charger on a small (motorcycle) AGM. It stank up the room, and swelled so it was difficult to pull out of the frame.

LiFePO4 also outgasses under conditions of abuse.
 
Hedges said:
Did your nose alert you?

I left a charger on a small (motorcycle) AGM. It stank up the room, and swelled so it was difficult to pull out of the frame.
Click to expand...
Yes, kept thinking the septic was backing up somewhere :LOL:.. I also did recently do some searching and saw that AGMs should never be placed in an enclosure without ventilation due to risk of hydrogen leakage.


LiFePO4 also outgasses under conditions of abuse.
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My understanding was that that is much less flammable than hydrogen gas coming out of a lead acid battery.
 
I commented this on the video just now:

Hey, very cool video. Nice pictures too. Fun to watch.

How much current feeds into the lead acid to trickle charge them at high SOC? Have you tracked what happens with a shunt between your batteries over a typical night?

At low SOC, it would seem the lead acid is reducing the performance of your system. Considering that the LiFePO4 wants to keep the voltage high, you couldn't use most of the capacity of your lead bank. I suppose the bms could disconnect and reconnect, but the differing internal resistances disconnecting and reconnecting seem a bit scary (could hurt fets). I suppose the lead acid does act as a buffer. Hmmm.

I would have to see how they feed each other over a cycle. That is difficult to do without a data logging device. Have you done that yet?

I see, so small lithium battery, big lead bank. Hmm I suppose that is attractive for a marine system.

Have you done a full capacity test? How deeply do you discharge your bank? If you keep this bank at high SOC, and none of the cells short, it would probably work fine.

Good point about setting absorption at 14V. Very true.

The prices of lifepo4 are dropping quickly. I built a 280Ah 12V pack for $580 this week. That is cheaper than high quality lead acid, if coulombic efficiency and usable capacity are taken into consideration.

You should try LTO. LiFePO4 is touchy, but that is only if you do not have a BMS. LTO would destroy every downside of LiFePO4 you mentioned. You can discharge at 10C rate! You can start any size engine with a modest size pack. You would love them I bet. Everything you stated in this video screams LTO. I did try paralleling LTO and LiFePO4 some years ago, and it was horrible. My capacity test results were awful. LTO has a wider voltage range, and more linear. And my test results were awful because of it. The cells would feed each other constantly. Very inefficient. Trickle charging lead acid all night with lithium seems very inefficient. I suppose if your loads are small, you can do it. Just that difference in voltage at various SOC makes me cringe.

Do you have any data logged on how the batteries feed each other during a full cycle?? I would love to see it.
 
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Will Prowse said:
I commented this on the video just now:

Hey, very cool video. Nice pictures too. Fun to watch.

How much current feeds into the lead acid to trickle charge them at high SOC? Have you tracked what happens with a shunt between your batteries over a typical night?

At low SOC, it would seem the lead acid is reducing the performance of your system. Considering that the LiFePO4 wants to keep the voltage high, you couldn't use most of the capacity of your lead bank. I suppose the bms could disconnect and reconnect, but the differing internal resistances disconnecting and reconnecting seem a bit scary (could hurt fets). I suppose the lead acid does act as a buffer. Hmmm.

I would have to see how they feed each other over a cycle. That is difficult to do without a data logging device. Have you done that yet?

I see, so small lithium battery, big lead bank. Hmm I suppose that is attractive for a marine system.

Have you done a full capacity test? How deeply do you discharge your bank? If you keep this bank at high SOC, and none of the cells short, it would probably work fine.

Good point about setting absorption at 14V. Very true.

The prices of lifepo4 are dropping quickly. I built a 280Ah 12V pack for $580 this week. That is cheaper than high quality lead acid, if coulombic efficiency and usable capacity are taken into consideration.

You should try LTO. LiFePO4 is touchy, but that is only if you do not have a BMS. LTO would destroy every downside of LiFePO4 you mentioned. You can discharge at 10C rate! You can start any size engine with a modest size pack. You would love them I bet. Everything you stated in this video screams LTO. I did try paralleling LTO and LiFePO4 some years ago, and it was horrible. My capacity test results were awful. LTO has a wider voltage range, and more linear. And my test results were awful because of it. The cells would feed each other constantly. Very inefficient. Trickle charging lead acid all night with lithium seems very inefficient. I suppose if your loads are small, you can do it. Just that difference in voltage at various SOC makes me cringe.

Do you have any data logged on how the batteries feed each other during a full cycle?? I would love to see it.
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Hey Will, cool to speak to Da Man. lol. This was not my video. it was just a topic that caught my eye and I was looking for feed back. I have actually turned my attention from this Idea due to so many unknowns, your new ones included. I think I am just going to use the 280ah "'B" cells from this video of yours to start. Even at a considerable diminished capacity the dollar value would be way up there. So, like in 10 years I'll have a 200ah battery... it's pretty much a no brainer. It's getting built in a pelican case to protect those wussy leads, so it will be fine. Thx for all the help!
 
Hi I'm Clark. I'm the guy in the video.
You are all right to be concerned with the charging and reconnect issues. I agree that a dc-dc charger is not the right solution for this problem for the reasons listed above. The lead would prefer a longer time cooking under the solar panels. I made another video describing the other side of this (from my point of view)

And I will be making one video about something that you guys might find interesting.
I've developed a circuit that disconnects the lithium batteries when they are charged fully and only reconnects when both banks meet at the same voltage so there is no problem with inrush current.
This circuit diagram will be made available for anyone who is handy with a soldering iron and I might do a production run for resale if there is interest.
 
Will Prowse said:
How much current feeds into the lead acid to trickle charge them at high SOC? Have you tracked what happens with a shunt between your batteries over a typical night?

At low SOC, it would seem the lead acid is reducing the performance of your system. Considering that the LiFePO4 wants to keep the voltage high, you couldn't use most of the capacity of your lead bank. I suppose the bms could disconnect and reconnect, but the differing internal resistances disconnecting and reconnecting seem a bit scary (could hurt fets). I suppose the lead acid does act as a buffer. Hmmm.

I would have to see how they feed each other over a cycle. That is difficult to do without a data logging device. Have you done that yet?

I see, so small lithium battery, big lead bank. Hmm I suppose that is attractive for a marine system.
Click to expand...
Lead is insanely good in providing high C discharge rates. (trawler motor) Further it charges at low temperatures. (not efficient but it charges)

I just looked up 6x 6V 225ah Lead batteries - Trojan - for just $480 - that's 8640wh 15wh/Dollar
The 280AH cells (no BMS, no wiring) 3584wh alone are are only giving only 6wh/Dollar
If you factor in all BMS, case etc. in the 4wh/Dollar.

So the lead batteries are still only 1/4 of the price of lead. With this combination lead+ lithium - you can potentially avoid the shortcomings of both. Even if you use the 50% discharge rule of lead - still half the price. In application where you need the weight (forklift, boats, house)

Charging under freezing - the lead part still charges
High efficiency solar charging during the day - to the lithium side
keep the lead above 70% for long cycle life (lead gets 1000+ cycles at this)
produce super high current (which lithium just can't do) 5C for engine start

It's definitely a interesting idea which suggest - further research is required in this topic.
 
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Will Prowse said:
I commented this on the video just now:

Hey, very cool video. Nice pictures too. Fun to watch.

How much current feeds into the lead acid to trickle charge them at high SOC? Have you tracked what happens with a shunt between your batteries over a typical night?

At low SOC, it would seem the lead acid is reducing the performance of your system. Considering that the LiFePO4 wants to keep the voltage high, you couldn't use most of the capacity of your lead bank. I suppose the bms could disconnect and reconnect, but the differing internal resistances disconnecting and reconnecting seem a bit scary (could hurt fets). I suppose the lead acid does act as a buffer. Hmmm.

I would have to see how they feed each other over a cycle. That is difficult to do without a data logging device. Have you done that yet?

I see, so small lithium battery, big lead bank. Hmm I suppose that is attractive for a marine system.

Have you done a full capacity test? How deeply do you discharge your bank? If you keep this bank at high SOC, and none of the cells short, it would probably work fine.

Good point about setting absorption at 14V. Very true.

The prices of lifepo4 are dropping quickly. I built a 280Ah 12V pack for $580 this week. That is cheaper than high quality lead acid, if coulombic efficiency and usable capacity are taken into consideration.

You should try LTO. LiFePO4 is touchy, but that is only if you do not have a BMS. LTO would destroy every downside of LiFePO4 you mentioned. You can discharge at 10C rate! You can start any size engine with a modest size pack. You would love them I bet. Everything you stated in this video screams LTO. I did try paralleling LTO and LiFePO4 some years ago, and it was horrible. My capacity test results were awful. LTO has a wider voltage range, and more linear. And my test results were awful because of it. The cells would feed each other constantly. Very inefficient. Trickle charging lead acid all night with lithium seems very inefficient. I suppose if your loads are small, you can do it. Just that difference in voltage at various SOC makes me cringe.

Do you have any data logged on how the batteries feed each other during a full cycle?? I would love to see it.
Click to expand...
Hi Will,
I've tried everything I can think of to PM you. If you are interested in talking about this contact me.

Clark
 
eXodus said:
Lead is insanely good in providing high C discharge rates. (trawler motor) Further it charges at low temperatures. (not efficient but it charges)

I just looked up 6x 6V 225ah Lead batteries - Trojan - for just $480 - that's 8640wh 15wh/Dollar
The 280AH cells (no BMS, no wiring) 3584wh alone are are only giving only 6wh/Dollar
If you factor in all BMS, case etc. in the 4wh/Dollar.

So the lead batteries are still only 1/4 of the price of lead. With this combination lead+ lithium - you can potentially avoid the shortcomings of both. Even if you use the 50% discharge rule of lead - still half the price. In application where you need the weight (forklift, boats, house)

Charging under freezing - the lead part still charges
High efficiency solar charging during the day - to the lithium side
keep the lead above 70% for long cycle life (lead gets 1000+ cycles at this)
produce super high current (which lithium just can't do) 5C for engine start

It's definitely a interesting idea which suggest - further research is required in this topic.
Click to expand...
Hey @eXodus - I'm having trouble with some of your numbers. 6x Trojan T-105's for $480?! The cheapest I could find is $134/ea, which would be $804 for 6 of them. And 6x 6V 225Ah is 8100Wh, not 8640Ah, unless I'm missing something. 8100Wh for $804 is 10Wh/$, and if you limit it to 50% DoD that's 5Wh/$.

You didn't show the numbers you were using for LFP, but it looks like you are saying $600 for 4x 280Ah cells, and another $300 for the BMS and other misc. items. I guess those are possible.

The only reason I care is that I have been keeping an eye on LFP and AGM prices, and for about the same Wh I think LFP is cheaper now.
 
rhino said:
One of the main advantages of LiFePO4 is not outgassing. The failure state of an older AGM battery is outgassing hydrogen (I had a 220Ah 48V bank fail and started outgassing). That alone would prevent me from wanting to mix the two.
Click to expand...
I was very surprised to hear this as virtually all UPSs have AGM batteries, and are located inside homes & offices. I have three AGMs under my desk right now. Instead of further hijacking this thread I would greatly appreciate your sharing any experiences in the Lead Acid Batteries forum.
 
Delmar said:
I was very surprised to hear this as virtually all UPSs have AGM batteries, and are located inside homes & offices. I have three AGMs under my desk right now. Instead of further hijacking this thread I would greatly appreciate your sharing any experiences in the Lead Acid Batteries forum.
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Just FYI (also not trying to hijack this thread) - All the UPSs I've ever seen have sealed Lead Acid batteries, NOT AGMs. That it, they are flooded lead acid, but sealed just like the "maintenance free" batteries for cars. AGMs generally don't off-gas Hydrogen, as the Hydrogen is absorbed by the glass matts. However, everything I heard when I was putting in the AGM batteries in our solar was to expect some small amount of hydrogen.

There may be some UPSs with AGMs. I just haven't seen them. If you pull the plastic top off of the little 12V batteries you'll see 6 little rubber caps over the flooded cells.
 
As a rough estimate the cross charging of the lead bank at LFP resting voltages is 0.25% of the Lead banks capacity. So a 100AH battery would use about 250mA. However this will vary quite a bit with temperature, lead battery type/brand, and age. So from 0.1% to 1% would be the expected range for deep cycle lead acid. Antimony alloy lead acid may use a fair bit more as they near end of life.

For most applications it doesn't make sense to mix lead and LFP.

There are however a few applications where this makes sense, and is in fact ideal.

Marine applications which power mission critical/safety loads. In these applications having a lead backup is sometimes cheaper than a second LFP pack with its own BMS. This yields redundancy in the case of the LFP battery faulting.

Some older equipment, especially on boats, can be very sensitive to voltage spikes. These can occur if the LFP pack drops out due to a fault during charging. This is often the case with cheap solar charge controllers, which don't have a fast response to a load shed. When this happens the main DC bus can spike to 16-20V (for a 12V system), which not all sensitive equipment can tolerate. By putting a small lead battery in parallel with the LFP battery, the lead battery absorbs voltage spikes, and provides power for a short period.

The major issue is that lead batteries need a long absorb time to achieve good life when deep cycled. This long absorb time is detrimental to LFP lifespan. While its not a major contributor, its still a consideration. Losing 5-10% of a expensive LFP batteries life just to continue using some lead doesn't always make sense. This isn't an issue where lead batteries are used as backup/buffer, as they aren't deep cycled.
 
Horsefly said:
Hey @eXodus - I'm having trouble with some of your numbers. 6x Trojan T-105's for $480?! The cheapest I could find is $134/ea, which would be $804 for 6 of them. And 6x 6V 225Ah is 8100Wh, not 8640Ah, unless I'm missing something. 8100Wh for $804 is 10Wh/$, and if you limit it to 50% DoD that's 5Wh/$.

You didn't show the numbers you were using for LFP, but it looks like you are saying $600 for 4x 280Ah cells, and another $300 for the BMS and other misc. items. I guess those are possible.
Click to expand...

Local store pickup in Southwest Florida, here are about a hundred golf courses around - they get pretty decent prices on batteries. Did your price of $134 include core charge? Shipping? The shop I looked at charges $28 per battery core charge.
Since you get that money back when you return those things I didn't count it.
It's like those car replacement parts - where they charge you a core. You have to return the old par.

Trojan batteries are rated as 6.4V - they run slightly higher voltages then other lead 6x6.4v x 225ah

I'm not saying it's for everybody and you will not get the same prices across the country.


It's just a interesting idea lead + lithium
 
I find this type of discussion interesting. I have been running a hybrid system for a year. Seems to me that the only ones ( I have heard only one person with issues, but was unsure of what caused it) Try to decide if it would work or not have never tried it. My FLA bank is 6 years old and using more water before I added the LFP bank. The reality (at least in my system) FLA mainly floats all the time. I have had a SCC failure and a BMS error (software error disconnect) and things did not skip a beat. I do not want things to shut down ( I don't know about you guys but when that happens it is usually NOT the best time for it) YMMV
 
EmilyAndClark's Adventure said:
I've developed a circuit that disconnects the lithium batteries when they are charged fully and only reconnects when both banks meet at the same voltage so there is no problem with inrush current.
This circuit diagram will be made available for anyone who is handy with a soldering iron and I might do a production run for resale if there is interest.
Click to expand...
It seems to me the circuit you propose would be the ideal way to make lithium / lead hybrid work, as you’re dispensing with the drain the lithium battery sees from the lead battery‘s self-discharge.

Did you put that circuit online yet and if so, could you point me to it? Thanks
 
Sverige said:
It seems to me the circuit you propose would be the ideal way to make lithium / lead hybrid work, as you’re dispensing with the drain the lithium battery sees from the lead battery‘s self-discharge.

Did you put that circuit online yet and if so, could you point me to it? Thanks
Click to expand...
He has a set survey up on his site. The more that do the survey the better the "chance" he will follow though. https://www.youtube.com/c/EmilyClarksAdventure/community
 
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