14.8v car battery to 12.6 3s Li-ion charger

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valueseek

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Hello everyone, this is my first post here and firstattempt at building a powerbank/powerwall. I've built a couple e-bike batteries before.Unfortunately my introduction also comes with a question, i have everything planned out for my setup except my question is;where can i finda charger??


I want to charge a 3s li-ion pack from the high ampalternator in my truck. I'd like for it to turn on automatically, so ido have a 12v switched power wire from the fuel pump that only turns on when the truck is running. I've used it to turn on an amplifier.

What can i use to do this? I will have 30 cells in parallel so 30a-45a would be ideal.An imax b6 can take 11v-18v but it goes to 5a max andwont start chargingautomatically. Are there anysolar charge controllersthat would work? What about a dc-dc converter, i knowthey arent made for li-ion though.

I know its not a common question because I've had a really hard time searching for a solution.I'm crossing my fingers and hopingsomeone here knows

https://www.aliexpress.com/item/Yan...53-4aca-bc18-7b6758099e9f&transAbTest=ae803_4

Maybe i should just use this and my 750w inverter?
 
First off, why 3s?
Secondly, did you read the FAQ? It's located on the main page.
Thirdly, what will you be running off this "12V" pack? you certainly won't be starting the engine, that's for sure
Quarterly, it has been asked before. Altho, I don't remember those who asked about it. Hmm, but searching for "charger 12V" only shows 1 result. Odd.
 
Yes i did read the FAQs, they do have a lot of good info. I didn't find anything about charging off of an alternator though.

I know its recommended to run 7s at the minimum due to voltages. My thinking is alot of 12v appliances will work ok at 10.6v-12.6v. The price of 24v to 12v converters put me off 7s but i just searched a little moreand found an 80 amp for $88 so maybe ill have to reconsider.
I want to run cheap 12v stuff, small inverters and cigarette lighter appliances. Heating blanket, fans, laptop and phone charger, maybe a piezoelectric cooler. No at the same time though. The 3s bms i was looking at is rated 80a so 850w max.

3s would probably work but if i can do it right for only $90 more maybe i will go with 7s. Ill bechecking how much the smartbms and high ampcharger will cost.
 
The alternator will typically try to charge the truck battery to around 14.1V before settling back to a float at 13.2V and this is the normal range you have to deal with.

The alternator will also try to deliver the maximum amps possible, so a discharged 3s pack connected directly to an alternator would have slight issues.

If it is a permanently connected charger/boost then yes a switch wire from something like the fuel pump would help prevent the lead-acid starter battery from discharging.

Search for "1500W boost" or "1200W boost" on ebay or aliexpress, they are these units.. if going 4s or 7s..
https://secondlifestorage.com/t-How-to-get-a-cheap-charger-with-over-100A-at-12V?pid=31192#pid31192
They would provide the CC CV charge source from the truck and you still need a BMS...
 
I guess this might work, and my 750w inverter should be able to handle it. Is using an inverter the best way to charge off of 12v?

https://www.aliexpress.com/item/29-...b5-4f3e-bfc5-3678bd235b49&transAbTest=ae803_4

EDIT: Ok thank you ill check them out. Connecting the lithium pack directly would have issues i agree.

EDIT2: I read your thread, some parts are over my head but its extremely interesting and definitely something ill read a few more times and refer back to in the future. Seems like with my limited knowledge, an inverter powered charger might be my best option.
 
You would be better off going with either 4s, or going 4s LiFePO4's. LiFePO4 cells are perfect for 12V systems and there's no need to worry about the over/under voltage issues like you do with LiCo cells. They are a little more pricey for the cell, but that would be negated by the lack of extra equipment you'd need to have to run the LiCo's properly.

As completelycharged stated, 14.1 is pretty much the top end voltage. However, I've seen them up to 14.4V, and some alts will even go to 15V (depends on your year/make/model).

LiCo:
3.0V * 3 = 9V | 4.2V * 3 = 12.4V
3.0V * 4 = 12V | 4.2V * 4 = 16.8V

LiFePO4:
2.8V * 4 = 11.2V | 3.6V * 4 = 14.4V

LiFePO4's can also handle being overcharged better than LiCo's can, as well. So if they get charged to 15V, they won't over heat and potentially explode like LiCo's can possibly do. So this also makes them safer in a vehicle.
 
https://www.ebay.com/sch/i.html?_from=R40&_nkw=1500w+step+up+converter&_sacat=0&_sop=15

The 1500w boost converter that completlycharged posted might actually work for me if it gives a stable voltage and i can charge the pack off it directly. I would consider going LiFePo4 more if i didn't already have 100 lg hg2 li-ion batteries.

I heard that some 12v inverters wont work on more than 15v. I suggested 3s originally because i i read 3.6v-4.2v is ideal for long battery life of 18650 li-ion cells. So if i did that i would stop discharging around 10.8. I'm not against 4s at all, and you all know more than me, im just confused as to how that would work.

Edit: I'm still lost, if the buck/boost converters dont have an adjustable current limit, then when its connected to the battery will it just trip short circuit protection or overcurrent protection and turn off?
 
It's not 3.6-4.2 for cell longevity. It's 3.2-4.1 range. Between 3.2 and 3.6V, there's still a lot of capacity available to you, and you'd be loosing out on it with a 3s configuration and your proposed cutoff voltage.


The buck/boost converters limit inrush current, so they won't trigger any protection. The current limiting factor is on the output and is for setting from "Max" output (which is usually 3A max, but there are some 5A units) down to <500mA. But not all units have the output current limiting pot.
 
The buck/boost units have 3 blue adjustable resistors on them - check the image in my post.
The first one nearest the input is the input voltage level cut-off - this would be useful for you to set at 13V as this would then prevent the truck battery from being discharged.
The second one in the middle is the current setting.
The last one near the output is the voltage level.
Try it hooked up to an adjustable power supply first off as this helps to set the input cut-off and adjusting the output.

Forgot to add and mention as a reminder for other people as well. The boost units will be fine on 12V and probably 24V but when hooking up to 48V if the otuput side is not pre-charged the inrush when connecting them to 48V blows the FET. Basically, hook up the output to the battery first and then connect to a supply if dealing with 48V packs that can deliver a lot of current. This is what I discovered charging 48V and 72V packs from a 50V power supply...

They seem to have a fault with the design (hence the price) where connecting to a large input voltage the unit tries to charge the output capacitors (which appear as a short circuit initially) drawing more current than the FET can handle but not enough time to blow the input fuses. There is an old saying in that the transistors/FET's blow to protect the fuses...
 
Ok makes sense, thanks.

I found this video about the same problem.
To summarize, his inverter works from 10v-16v. He can either use 4s and undercharge to 4v,or 3s and under-discharge to 3.3v. He calculated that 4s looses less with his equipment, but also mentioned most inverters do not work up to 16v.

Maybe i should just go with 7s. With 3s i wouldneedto buy way more batteries and with 4s i would needto buy new 16v inverters and buck converters for 12v stuff.

A new 750w inverter would be $25 or a little more if i went bigger/pure sine wave. A 24v-12v 40aconverter would also be $25. The same or less money than making 3s-4s work.

https://www.aliexpress.com/item/100...17-4948-bb5e-63ae038e2fe5&transAbTest=ae803_4

https://www.aliexpress.com/item/24V...64-47fc-876a-1596c1f40822&transAbTest=ae803_4
 
valueseek said:
Hello everyone, this is my first post here and firstattempt at building a powerbank/powerwall. I've built a couple e-bike batteries before.Unfortunately my introduction also comes with a question, i have everything planned out for my setup except my question is;where can i finda charger??
Click to expand...

welcome! questions are good here, especially ones with as much detail as you have included.


I want to charge a 3s li-ion pack from the high ampalternator in my truck. I'd like for it to turn on automatically, so ido have a 12v switched power wire from the fuel pump that only turns on when the truck is running. I've used it to turn on an amplifier.
Click to expand...


most of us avoid 3s as it cant (easily/normally) be used for running AC inverters. however, you do not specify any such requirement, so I think 3s sound ok to me.

I would very much recommend that you use a relay to switch your charger on and off though. it seems unlikely that any fuel pump power feed is going to be happy carrying the current you want. a horn relay/kit should be a good fit.


What can i use to do this? I will have 30 cells in parallel so 30a-45a would be ideal.
Click to expand...

that is a serious amount of power from the alternator etc ... (!) 20A might be an easier target ...


An imax b6 can take 11v-18v but it goes to 5a max andwont start chargingautomatically. Are there anysolar charge controllersthat would work? What about a dc-dc converter, i knowthey arent made for li-ion though.
Click to expand...

you may want to consider a Ruideng DPS5015 DC-DC buck converter. it only shifts power down in voltage, so you would always need 10% higher voltage on the input side ... thats 12.0V *1.1 = 13.2V minimum required to charge 12V ... the current is limited to 15A ... which I find never to be a limiting factor for my uses ... and it can be set to turn on on powerup! It is a CC-CV PSU, so the output current can be set/reduced, if you wanted to. Use an affiliate link from the forum here to share a kickback, if you buy.


Maybe i should just use this and my 750w inverter
Click to expand...


I used to invert up to AC and then back down to DC myself, when running a 48V POE switch in my car, as it seemed the easiest just to use existing AC PSU, as you suggest here. it was a pain in the neck, and always 'felt very wrong' to me. for complexity, reliability, efficiency, and high power throughput reasons, I would avoid this route. stick with your plan of DC to DC charging.
 
valueseek said:
Ok makes sense, thanks.

I found this video about the same problem.
To summarize, his inverter works from 10v-16v. He can either use 4s and undercharge to 4v,or 3s and under-discharge to 3.3v. He calculated that 4s looses less with his equipment, but also mentioned most inverters do not work up to 16v.

Maybe i should just go with 7s. With 3s i wouldneedto buy way more batteries and with 4s i would needto buy new 16v inverters and buck converters for 12v stuff.

A new 750w inverter would be $25 or a little more if i went bigger/pure sine wave. A 24v-12v 40aconverter would also be $25. The same or less money than making 3s-4s work.

https://www.aliexpress.com/item/100...17-4948-bb5e-63ae038e2fe5&transAbTest=ae803_4

https://www.aliexpress.com/item/24V...64-47fc-876a-1596c1f40822&transAbTest=ae803_4
Click to expand...

I'm pretty sure if you go with either of those inverters, you'll be replacing them in less than 6 months. The first one looks like a Reliable rebranded inverter.
A lot of those cheap 12/24V inverters aren't really all that great. The 48V models are usually better built.

If you plan on running "any" inductive loads, you "need" to go pure sine way. Otherwise you'll be shortening the life of that device. So any motors running on AC need to use a pure sine inverter.
 
Id rather not leave a wall of text, so ill make a short list.
-Thanks, i like this forum a lot. I've always wanted to build a powerbank but never had a reason to spend the money until now.
-I just need to run a heating blanket at night. Ideally yes i'd like to have a small amount of AC power. ~350w to run a laptop charger, tv, and similar.
-I won't run any nice motors on modified sine-wave. Maybe a $2 usb fan. No drills, a/c, blenders, i also read coffee machines are a no-go sadly.
-I was hoping the inverters could last more than 6 months. I've had the same everstart 70003M 12v inverter from walmart for many years.
-I have a 2001 4x4 Suburban 1500 with a 5.3l, the alternator is 253a. If the amps is low it will take a really long time to charge.

Thanks for linking that buck converter, it seems really versatile. I think it should work for lithium, with the BMS doing the balancing. If i don't use it now, i might in the future for another project.
 
*Heating blanket will definitely need to run at 12V. If you dump 24V through it, it might catch fire. Better safe on that one all around.
*The laptop you could probably charge directly from DC. You would still use a buck converter to set the output voltage to the same as the laptop bricks output. Just make sure to get a buck that can handle at least the same amp output as the brick. You may need to parallel two units to achieve this.
*There are DC powered coffee makers out there (not sure of pricing, though). And, if there is too much smarts in it, it might not work on modified wave. I've seen a video where they had to turn on the blender first before turning on the coffee maker to create an inductive load which also smoothed out the wave somewhat. Then the coffee maker turned on. Odd. Too smart for it's own good, I suppose.
*The inverter from Wally is probably better quality than the ones you linked to earlier, too ;)
*As long as the alt can output 20A or more, you should be ok with charging from it
 
Haha if the heating blanket caught fire at least it would keep me pretty warm. Kidding yeah they make 12v blankets and i have a 50w ac mat so if i go with 24v i would need use either a inverter or buck converter. I know the ac powered blankets draw from 50a-200a+ but im not sure about the 12v blankets.

That smart coffee machine solution is pretty genius, i would've probably gave up found another coffee machine or used a french press if i had to. I guess i need to give walmart more credit for the inverter, it was only $50 too. Ill have to keep searching, not sure if a cheap pure sine wave would be any better.

As for the battery, im still looking at 24v, or maybe 13s 48v. 4s would work well with LiFePO4, but not Li-ion at 15v max, 3.75v per cell.

https://www.aliexpress.com/item/Pea...d3-41b6-8f28-49359d9ee6af&transAbTest=ae803_4
 
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