DC/DC or ArgoFet

[s/v Jedi]

Originally Posted by Philtao

Sorry I am late in the discussion, but to go back to the original question I would like to share a simple way it can be done using the TAO BMS.
This is for an installation with a FLA starter battery and a LiFePo4 house battery, using an alternator with external regulator set to charge the lithium battery (13.8 v for me). I like to keep it simple with minimum cables, connections and equipment between the chargers and the battery - so no DC/DC charger and no battery isolator (maybe that can help compensate for the price difference ).

My original assumption (which I have now validated over the last 3 years) is that trickle charging the starter FLA battery between 13.2 and 13.8 volt most of the time keeps it full and healthy... my starter battery is 5 years old now and when it is disconnected from the lithium battery, its rest voltage is 12.8 v. that keeps me happy and even if I have to replace it in a year or two it is a decent service life for less than USD150.

As suggested earlier in this thread the basic principle is to have the lithium and FLA batteries in parallel BUT:

• avoid draining the FLA battery when the lithium battery is low
• and use the FLA battery as a safety backup in case the BMS shuts down the lithium battery (quite important on a boat)

In summary:
The FLA battery is connected in parallel with the lithium battery when:

• the ignition is turned on (and no high voltage situation requiring to stop the charge)
• or the cell voltage or SOC are above set thresholds (example: 3.25 v / 50% SOC)
• or just before the lithium battery is disconnected by the BMS

The FLA battery is disconnected from the lithium battery when:

• the BMS detects a high voltage situation that requires to stop the charge
• or the cell voltage or SOC are below set thresholds

If you would like me to explain in details how it is done with the BMS, it might be better to open a new thread so that this one does not get side tracked.

Instead of using the ignition signal to parallel the batteries, use the oil pressure switch or alternator output detection, so that the surge from starting the engine is isolated to the starting battery and kept away from electronics.

[Philtao]

Originally Posted by s/v Jedi

Instead of using the ignition signal to parallel the batteries, use the oil pressure switch or alternator output detection, so that the surge from starting the engine is isolated to the starting battery and kept away from electronics.

Great suggestion - thanks.

[CaptainRivet]

Originally Posted by Philtao

Great suggestion - thanks.

Or just ditch that starter FLA completely and simplify even more.
if you have an external regulator and can charge the LifePo4 plus your BMS does not carry current works perfect.
If its a small bank, its a small boat aed a small engine and vice versa so the lifepo4 can handle the surge. Check that.
Backup 6 LTO cells in series, no BMS, charged by a flexible 50W solar panel and MPPT and a battery switch. The AH a start takes is mnimal and that 50W panel fits on every boat, that LTO cost 300 and does 30000cycles =54years if cycled daily. It will always start your engine. Lifepo4 down, flip the switch, start the engine and flip it back and your LifePo4 gets charged.
LTO can be charged with LifePo4 profil to do the major charge, the rest the slar can do and keep it maintained

[s/v Jedi]

Originally Posted by CaptainRivet

Or just ditch that starter FLA completely and simplify even more.
if you have an external regulator and can charge the LifePo4 plus your BMS does not carry current works perfect.
If its a small bank, its a small boat aed a small engine and vice versa so the lifepo4 can handle the surge. Check that.
Backup 6 LTO cells in series, no BMS, charged by a flexible 50W solar panel and MPPT and a battery switch. The AH a start takes is mnimal and that 50W panel fits on every boat, that LTO cost 300 and does 30000cycles =54years if cycled daily. It will always start your engine. Lifepo4 down, flip the switch, start the engine and flip it back and your LifePo4 gets charged.
LTO can be charged with LifePo4 profil to do the major charge, the rest the slar can do and keep it maintained

I would much rather dedicate a small dc-dc charger to charging the starter battery bank than a solar panel!

[Statistical]

Originally Posted by s/v Jedi

I would much rather dedicate a small dc-dc charger to charging the starter battery bank than a solar panel!

Exactly. I don't think some people realize just how little energy is used to start a motor. It is in the ballpark of 1Ah (10Wh)*. Even if you start your motor three times in a day that is still a trivial amount of energy.

Even a small solar panel will produce a lot more than that. All (as in all) energy sources into larger house bank. Small DC to DC charger to charge the start battery.


* Example: 200A starter running for 15 seconds = 200A * 13V * 15s /60 /60 = ~10Wh

[CaptainRivet]

Originally Posted by s/v Jedi

I would much rather dedicate a small dc-dc charger to charging the starter battery bank than a solar panel!

And how do you charge your emergency backup LTO if your LifePo4 is shut down? An LTO even down to 8V starts an 7lV8 engine or a 100hp diesel. I tried myself.
So if all is down, mean really all down to 0V. Just 2h of sunshine and your LTO starts your diesel and you are back on power. Try this with FLA....
You actually don't need solar or dc to dc. Just a 1 or 2 switch.
You can boost charge the LTO directly from the alternator if your engine runs, it takes 10C charge and discharge also in LifePo4 profil. Yes its only 80% full but doesn't care. No need for additional equipment. solar is just last resort backup that needs no maintenance at all, it just works.
That's why simple.
Your reliable and long-lasting lifepo4 does all well supervised by BMS, in emergency case flip a switch and you have a backup LTO that always starts your engine, has no self discharge and takes all the charge that you throw at it, small or huge from any source you have on board.

[CaptainRivet]

Originally Posted by Statistical

Exactly. I don't think some people realize just how little energy is used to start a motor. It is in the ballpark of 1Ah (10Wh)*. Even if you start your motor three times in a day that is still a trivial amount of energy.

Even a small solar panel will produce a lot more than that. All (as in all) energy sources into larger house bank. Small DC to DC charger to charge the start battery.


* Example: 200A starter running for 15 seconds = 200A * 13V * 15s /60 /60 = ~10Wh

Exactly. And now when it runs throw the 150A of your big alternator at the 40AH LTO for 10min and the LTO is full and ready to emergency start your engine for the next 18 month without any recharge or other maintenance stuff, its just there
always ready to get you out of trouble.
You don't need a dc to dc charger,waste of money. Flip the switch during a year for 3min whenever you feel or think about it... If you forget alos not a problem.
Have a 50W solar panel and if its open circuit voltage is below 17V you don't even need a charger, LTO regulates what it needs and is always full without any maintenance at all. Fantastic last emergency resort...

[Philtao]

Originally Posted by CaptainRivet

Or just ditch that starter FLA completely and simplify even more.
if you have an external regulator and can charge the LifePo4 plus your BMS does not carry current works perfect.
If its a small bank, its a small boat aed a small engine and vice versa so the lifepo4 can handle the surge. Check that.
Backup 6 LTO cells in series, no BMS, charged by a flexible 50W solar panel and MPPT and a battery switch. The AH a start takes is mnimal and that 50W panel fits on every boat, that LTO cost 300 and does 30000cycles =54years if cycled daily. It will always start your engine. Lifepo4 down, flip the switch, start the engine and flip it back and your LifePo4 gets charged.
LTO can be charged with LifePo4 profil to do the major charge, the rest the slar can do and keep it maintained

Yes, I told myself a while ago that I need to get one of those LTO packs... just in case! Thanks for getting me back on track.
Do you have any recommendations / or experience with specific ones (or those to avoid)

[CaptainRivet]

Originally Posted by Philtao

Yes, I told myself a while ago that I need to get one of those LTO packs... just in case! Thanks for getting me back on track.
Do you have any recommendations / or experience with specific ones (or those to avoid)

40AH Yinglong cells, the 40AH are the best production quality. They also produce 30AH in the same size, worth get the 40. They also produce larger 55AH,avoid them quality problems. All other AH sizes are derated 40AH or 55AH...
If you get 35AH grade B from a good reliable source that state 36-38AH and guarantee they are new for a good price go for them. These are 40AH didn't meet specs....
Be careful most derated are heavyly used in public korean buses or energy storage and newly wrapped mostly 40AH,avoid.

You can put 6 in series with long 10mm nuts connecting studs together and put them in a pvc pipe and hang them on the ceiling or corner.
Cheap, Space saving and mechanically sound way

[CaptainRivet]

Important on LTO is a 100% proper top balance before assembly. Recommend running the process twice and let them sit for 48h in parallel.
For 5 or 6 cells in series in a 1 or 2p6S never 100% need a BMS and up to 4p6S you don't need a BMS on the Yinglong, yes the maybe loose 5000 of there 30000 cycles but used as starter they hardly cycle anyhow. Suggest to Charge them to 16V max so with cable loses no gear on your boat sees effectively more then 15,5V,yes they are only 90% full and capacity like this. they don't care. You will still see 50years+
BUT if you are running 24V means 11 or 12 cells series or above you MUST use a BMS with a good(!) active balancer, the cells start to drift apart quite soon and balancer need to fix it.
Friends have a NPO producing a huge 48V 800AH bank called Titan for offgrid with these 40AH Yinglong cells since 10 years and have a vast experience with them.
Can be charged till - 30 degrees celcius
Had 6 LTO 40AH Yinglong in 1p6S no BMS in my AudiR8 replacing 110AH AGM for 4 years starting it daily with a big 2200W stereo. No problem and never needed grid charge in this 4 years and new owner last 2 years either...Audi R8 has quite a high power demand. AGM died all 2 years, couldn't handle it.

[Philtao]

Originally Posted by CaptainRivet

Important on LTO is a 100% proper top balance before assembly. Recommend running the process twice and let them sit for 48h in parallel.
For 5 or 6 cells in series in a 1 or 2p6S never 100% need a BMS and up to 4p6S you don't need a BMS on the Yinglong, yes the maybe loose 5000 of there 30000 cycles but used as starter they hardly cycle anyhow. Suggest to Charge them to 16V max so with cable loses no gear on your boat sees effectively more then 15,5V,yes they are only 90% full and capacity like this. they don't care. You will still see 50years+
BUT if you are running 24V means 11 or 12 cells series or above you MUST use a BMS with a good(!) active balancer, the cells start to drift apart quite soon and balancer need to fix it.
Friends have a NPO producing a huge 48V 800AH bank called Titan for offgrid with these 40AH Yinglong cells since 10 years and have a vast experience with them.
Can be charged till - 30 degrees celcius
Had 6 LTO 40AH Yinglong in 1p6S no BMS in my AudiR8 replacing 110AH AGM for 4 years starting it daily with a big 2200W stereo. No problem and never needed grid charge in this 4 years and new owner last 2 years either...Audi R8 has quite a high power demand. AGM died all 2 years, couldn't handle it.

Thank you CaptainRivet for all these precious information. It looks like I need to do some reading and, once I understand the possibilities, define my exact requirements before I embark on that route.
It is not a plug and play, so it will have to wait a bit as for the moment I am too busy dealing with semiconductor shortage and building BMS's

[rocks]

Hi I have been using LTO's as a starting battery for over four years. The LTO's replaced a 850 cca battery and the engine starts a lot faster with the LTO's. The battery set is made up with 6 X 40 amp cells in series.
Charging system consists of a 10 watt Amorphis solar panel and the motor’s 80 amp alternator. I do not use a balancer for the LTO's battery.
The only problem I have had is that the battery will not keep up with the glow plugs on a six cylinder Yanmar. This is not really a problem as we are in the tropics.
As a backup for starting if the LTO fails I have a super capacitor which I have never used other than starting other people's cars at the marina.

[Britishsea]

Originally Posted by rocks

Hi I have been using LTO's as a starting battery for over four years. The LTO's replaced a 850 cca battery and the engine starts a lot faster with the LTO's. The battery set is made up with 6 X 40 amp cells in series.
Charging system consists of a 10 watt Amorphis solar panel and the motor’s 80 amp alternator. I do not use a balancer for the LTO's battery.
The only problem I have had is that the battery will not keep up with the glow plugs on a six cylinder Yanmar. This is not really a problem as we are in the tropics.
As a backup for starting if the LTO fails I have a super capacitor which I have never used other than starting other people's cars at the marina.

Great to have real world user feedback on a 40ah LTO starter battery. My current AGM starter is almost dead, and at the replacement cost I'm tempted to go 40ah LTO yinlong.

Surprised the LTO could not manage your 6 glow plugs. Too much current draw I assume?

I typically run my electric winch off my start battery. The engine is running when we put up the main sail. Typically after that it's only used in short bursts when the engine goes off. Unclear to me if it's unrealistic to expect that a 40ah LTO could manage this....

BritSea

[CaptainRivet]

Originally Posted by rocks

Hi I have been using LTO's as a starting battery for over four years. The LTO's replaced a 850 cca battery and the engine starts a lot faster with the LTO's. The battery set is made up with 6 X 40 amp cells in series.
Charging system consists of a 10 watt Amorphis solar panel and the motor’s 80 amp alternator. I do not use a balancer for the LTO's battery.
The only problem I have had is that the battery will not keep up with the glow plugs on a six cylinder Yanmar. This is not really a problem as we are in the tropics.
As a backup for starting if the LTO fails I have a super capacitor which I have never used other than starting other people's cars at the marina.

Well 6 glowplugs on a 40AH with 10C=400A constant is really a bit undersized, i bet the 850ccca was on the limits too in this case. Solution just add another 6 pack LTO 40AH in parallell and job done.

[CaptainRivet]

Originally Posted by Britishsea

Great to have real world user feedback on a 40ah LTO starter battery. My current AGM starter is almost dead, and at the replacement cost I'm tempted to go 40ah LTO yinlong.

Surprised the LTO could not manage your 6 glow plugs. Too much current draw I assume?

I typically run my electric winch off my start battery. The engine is running when we put up the main sail. Typically after that it's only used in short bursts when the engine goes off. Unclear to me if it's unrealistic to expect that a 40ah LTO could manage this....

BritSea

The 40AH LTO will manage your windlass easily, assume its a 1000 or 1400W one. It may have around 100-160a continuous and 400A surge, LTO can do 400A cont and 800A peak.
6 glow plugs are 600A for 2 sec minimum plus cranking amps and that's just too much,assume his 850ccca was also on the limits before. 1 glow plug is not a problem but if you have common rail
with 3-6plugs then you need min 60AH LTO, better 80AH.
Be careful LTO has a low resistance like lithium so you loose your high resistant protection in your LI system if via an argofet.