float charging lifepo4

bike4life · Jul 16, 2021

i have a trailer with a generator attached to the ebike. the trailer is attached to bike seatpost
the 2000w generator powers a 1000w switching supply and 1500w boost converter which can be adjusted to make any arbitrary DC voltage.

i plan on having an infinitr range ebike / gas hybrid ebike. in this way the bike can be charged as fast as its discharged allowing for unlimited range.

the question is i am using a123 cell lifepo4 batteries - 12s / 8p, and i am wondering what the best float voltage for my trailer contraption. I do not want excessive wear on the cells, as on every bike trip the generator will be running which means i will accumulate lots of charging cycles. I heard it is better to then since i am using these batteries kind of like a giant capacitor bank to float a lower voltage like 40v or something like that for longetivity. Thanks

dogman dan · Jul 17, 2021

Use a regular charger and bms to balance charge the batteries once back home, periodically. They need this, but if your pattern of use is gentle enough, they may only need it a few times a year. To keep the lifespan, simply discharge back to your voltage choice asap after you balance the batteries. THEY DO need top balancing anytime they get used harshly, like high rate discharges, or 100% discharged.

But you can set your voltage on the generator rig to a lower voltage, say 80% charged. That way you don't overcharge while riding, spending time on the road with the cells 100% charged, or more if they are not perfect balanced.

It would still be best to keep a bms on them out on the road, just in case a cell group decides to get overcharged. Or perhaps some kind of device that will warn you about overcharge or overdischarge of any cell group. 12 voltmeters would be a pain to watch all day, but you could have that on the trailer, just to keep an eye on things.

Why the boost converter? Can't you just get a power supply that can adjust to your desired voltage?

Even better, perhaps later on,, get a satiator charger from Grin. Waterproof, with full adjustability for voltage. This can do your charging on the road, or at home. Your generator will run all day sitting in the rain, but your PS and stuff will need a dry box. The satiator can mount right on the trailer, in the rain.

MadRhino · Jul 17, 2021

That is a fail redundancy. Your ‘infinite range’ is an utopia and does rely on two systems with each their own vulnerabilities. Twice as many chances to fail, with a considerable efficiency loss and performance limitation.

If you are going to burn gas to travel, why would you want to handicap the efficiency and reliability by transforming the energy twice before producing motion? It would be much better and simpler to ride a gasser.

donn · Jul 17, 2021

MadRhino said:
If you are going to burn gas to travel, why would you want to handicap the efficiency and reliability by transforming the energy twice before producing motion? It would be much better and simpler to ride a gasser.

Maybe he's got something like a steam turbine that can operate much more efficiently, but needs to be used with a storage device because it operates at constant output.

AHicks · Jul 17, 2021

"float voltage" - There is no such thing available for LiFe or LiPo batteries to my knowledge. Any attempts to try will over charge them, and potentially lead to an overheated scenario they will not recover from.

The charge needs to shut down once the target voltage has been achieved.

bike4life · Jul 17, 2021

dogman dan said:
Use a regular charger and bms to balance charge the batteries once back home, periodically. They need this, but if your pattern of use is gentle enough, they may only need it a few times a year. To keep the lifespan, simply discharge back to your voltage choice asap after you balance the batteries. THEY DO need top balancing anytime they get used harshly, like high rate discharges, or 100% discharged.

But you can set your voltage on the generator rig to a lower voltage, say 80% charged. That way you don't overcharge while riding, spending time on the road with the cells 100% charged, or more if they are not perfect balanced.

It would still be best to keep a bms on them out on the road, just in case a cell group decides to get overcharged. Or perhaps some kind of device that will warn you about overcharge or overdischarge of any cell group. 12 voltmeters would be a pain to watch all day, but you could have that on the trailer, just to keep an eye on things.

Why the boost converter? Can't you just get a power supply that can adjust to your desired voltage?

Even better, perhaps later on,, get a satiator charger from Grin. Waterproof, with full adjustability for voltage. This can do your charging on the road, or at home. Your generator will run all day sitting in the rain, but your PS and stuff will need a dry box. The satiator can mount right on the trailer, in the rain.

yes i run a bms on them 100% of the time riding and charging. I forgot to mention that cause i thought everyone bms's their stuff.

bike4life · Jul 17, 2021

dogman dan said:
Use a regular charger and bms to balance charge the batteries once back home, periodically. They need this, but if your pattern of use is gentle enough, they may only need it a few times a year. To keep the lifespan, simply discharge back to your voltage choice asap after you balance the batteries. THEY DO need top balancing anytime they get used harshly, like high rate discharges, or 100% discharged.

But you can set your voltage on the generator rig to a lower voltage, say 80% charged. That way you don't overcharge while riding, spending time on the road with the cells 100% charged, or more if they are not perfect balanced.

It would still be best to keep a bms on them out on the road, just in case a cell group decides to get overcharged. Or perhaps some kind of device that will warn you about overcharge or overdischarge of any cell group. 12 voltmeters would be a pain to watch all day, but you could have that on the trailer, just to keep an eye on things.

Why the boost converter? Can't you just get a power supply that can adjust to your desired voltage?

Even better, perhaps later on,, get a satiator charger from Grin. Waterproof, with full adjustability for voltage. This can do your charging on the road, or at home. Your generator will run all day sitting in the rain, but your PS and stuff will need a dry box. The satiator can mount right on the trailer, in the rain.

yeah so my 36v powersupply if i turn the adjustment knob to 40v it actually doesnt like that and craps out on me. So i use a boost converter to go from 36v on the switchmode to 42 or what not. I googled the efficiency of a boost converter for a smaller step up and its roughly 90%. They are very bad for like 12v --> 48v in efficiency, but ok for small 15% upgrades in voltage.

bike4life · Jul 17, 2021

donn said:
MadRhino said:

If you are going to burn gas to travel, why would you want to handicap the efficiency and reliability by transforming the energy twice before producing motion? It would be much better and simpler to ride a gasser.

Click to expand...

Maybe he's got something like a steam turbine that can operate much more efficiently, but needs to be used with a storage device because it operates at constant output.

right so i am limited to 10 miles per a123 pack. I want to go more than 10 miles like around 200 miles on a charge. OK no battery system can handle that. So i have a generator. You are correct in using a gasser, however, small 66cc / 49cc gassers are technically illegal in my state in the USA but hybrid ebikes are not.

bike4life · Jul 17, 2021

AHicks said:
"float voltage" - There is no such thing available for LiFe or LiPo batteries to my knowledge. Any attempts to try will over charge them, and potentially lead to an overheated scenario they will not recover from.

The charge needs to shut down once the target voltage has been achieved.

I have a bms that will kill power past X voltage when they are charged. I am floating them at a low voltage like at 80% SOC so its impossible for them to ever go fully charged.

bike4life · Jul 17, 2021

MadRhino said:
That is a fail redundancy. Your ‘infinite range’ is an utopia and does rely on two systems with each their own vulnerabilities. Twice as many chances to fail, with a considerable efficiency loss and performance limitation.

If you are going to burn gas to travel, why would you want to handicap the efficiency and reliability by transforming the energy twice before producing motion? It would be much better and simpler to ride a gasser.

some quick math shows it will cost 50 cents per hour to run my high efficiency generator. 6 gallons per hour. 3.00 gas / 6 = 50 cents.
I am okay with paying 50 cents an hour to go 27mph, to go infinite range. Mind you the first 10 miles would be free until it runs low and i kick on the generator. the biggest problem is i want an ebike that will go any arbitrary distance, say 300 miles on a charge. Well, the only way to do that is a gas hybrid ebike which i built. Gassers are out of the question as 49cc / 66cc bicycles are illegal in my state.

john61ct · Jul 17, 2021

I agree the big picture is foolish, but setting that aside, thought experiment assuming everything is reliable.

3.32V to 3.35Vpc is your 100% Full target for sitting isolated at rest

3.0V is your 0% for minimum security

3.1V for decent longevity, same conditions.

So, a 3.3V charge input, at an Amps level slightly higher than your average Load consumption

will work just fine.

Sitting at lower voltage than that all the time is wasting capacity.

Sitting at Full with charge input continuing is not good for longevity.

If you see the pack is actually reaching that 3.3Vpc, staying there consistently for a few minutes on the flat, means you're very close to Full

it would be better for longevity to kill the gennie, let the pack discharge for a while

Watch your coulomb counter, and when you've discharged down to 30-40% SoC, start the gennie back up again

A bigger pack just lets that off cycle last longer.

john61ct · Jul 17, 2021

>a 3.3V charge input, at an Amps level slightly higher than your average Load consumption will work just fine.

Note, if the amps output of the genset is even slightly below the average discharge rate

you will inevitably run down your SoC to hit your LVC.

So factor in a heavier load, higher headwind and hillier than usual terrain

and/or size the pack bigger to help ride through such changes for a bit longer.

999zip999 · Jul 17, 2021

Why ?

bike4life · Jul 17, 2021

999zip999 said:
Why ?

why what

bike4life · Jul 17, 2021

john61ct said:
I agree the big picture is foolish, but setting that aside, thought experiment assuming everything is reliable.

3.32V to 3.35Vpc is your 100% Full target for sitting isolated at rest

3.0V is your 0% for minimum security

3.1V for decent longevity, same conditions.

So, a 3.3V charge input, at an Amps level slightly higher than your average Load consumption

will work just fine.

Sitting at lower voltage than that all the time is wasting capacity.

Sitting at Full with charge input continuing is not good for longevity.

If you see the pack is actually reaching that 3.3Vpc, staying there consistently for a few minutes on the flat, means you're very close to Full

it would be better for longevity to kill the gennie, let the pack discharge for a while

Watch your coulomb counter, and when you've discharged down to 30-40% SoC, start the gennie back up again

A bigger pack just lets that off cycle last longer.

currently i have 1 12s lifepo4 pack on the trailer and a 2300w start / 1800w run generator and a 1500w boost converter and a 1000w switchmode supply. I am currently limited by the 1000w switchmode so i cant dump more than 1000w of power. I currently did a brief 1/2 mile test before the generator got loose on the rachet strap ties to the trailer thankfully it didnt fall off, so i had to turn around and take it slow but with the additonal 50 pounds of the generator the top speed goes to 23-24mph at 40v. I am thinking of adding in my second lifepo4 pack for 80 volts, running a 1000w swicher in series with my 36v one to make 72, and boost convert to 80v so i can get maybe 35mph... I will buy a new boost converter rated for 1800w, so basically i can charge the batteries at 1800w consistently which should be good for 35mph? what do you think folks.

john61ct · Jul 17, 2021

I think overall, ridiculous.

But to be constructive, expand one LFP pack at the one desired system voltage.

Nothing but downside using voltage converters or keeping packs separate.

bike4life · Jul 17, 2021

doesnt matter if you think its ridicouous although my boost converter appears to be 95% efficient since i am stepping up only 15% voltage. you drop efficiency with a larger stepup. I do want to go faster so i need another pack in series.

JackFlorey · Jul 17, 2021

john61ct said:
I think overall, ridiculous.

Agreed. But there could be worse things he could be doing. Heck, if it distracts him, and he stops (say) smoking because he's distracted, it may even do him some good.

My suggestion is to drive the trailer wheel directly with the gas motor. Pretty much every DD hub out there is a motor and a generator; no need for a separate generator. The official term for this is "road linked hybrid." (And then you can remove the trailer and it's just an ebike.) And no DC/DC converter inefficiencies!

Heck, you could even cannibalize a gas scooter - remove the front of it and attach the rest of it as a trailer.

There were quite a few designs for gas powered pusher trailers for EV's back when battery capacity was a huge stumbling point.

JackFlorey · Jul 17, 2021

Duplicate

dogman dan · Jul 18, 2021

Interesting that 49cc gassers are illegal where he is.

Only reason I did not type "get a motorcycle or scooter" is that he did not want to go very fast.

But yeah, you want to have long range a lot, to carry that heavy generator around. I tried the same thing, but found that just buying two ping battery lifepo4 batteries gave me enough range for my desires at the time. I had 1500wh, and about 70 miles of range at 15mph. Around here, 70 miles gets you across the desert to another plug.

The two pings weighed about 30 pounds, my generator 50.

float charging lifepo4

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