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BMS for 4x4 cranking & winchinh

Werdna

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Joined
Dec 19, 2021
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15
Hi guys I have been researching a lifepo4 setup for my 4x4 and all roads seem to lead to this forum so I'm here asking for some help as I am a little out of my depth.

My old 4x4 has a single 250ah deep cycle AGM which runs a fridge, camp lights and the radio for a few days at a time with plenty of reserve for starting the engine.

New 4x4 has no room for dual batteries, or such a big single unit. It comes factory with a H9 AGM under the driver's seat. 190a (smart?) alternator, gasoline V8 turbo, 1.7kw starter motor.

I am from Australia. The coldest we see is around 0°C in winter. So no drastically high or lows temps for the battery to deal with.

I would like to replace the under seat battery with 4 x 200-280ah lishen or eve lifepo4 cells but choosing a BMS has me going around in circles.

Starter should draw 1700/12 =140 amps for let's say 5 seconds on average, or 30 seconds at a time during a no-start scenario.

Winch (not yet fitted) will anecdotally draw 200-400 amps when loaded up. Only used for 30 seconds, then allowed to cool.

Inrush current for both should be 2-3 times the above for <1 second?

Most prismatic cells seem to be good for 1C continuous or 2C for upto 30 seconds. Seems like 200ah cells would be on the limit but the 280ah would give me some headroom while stretching the budget.


1) do I just slap a 250a Daly on it and not worry? Best option looks like a 600a Chargery setup, but spendy. Or the 300a Chargery, maybe borderline. Any other options I've missed?

2) how come none of the 200-300a 12v pre-built lifepo4 batteries for sale are rated for cranking? Seems like they would have enough C rating and borderline enough BMS.

3) convince me I need a BMS at all. Why not spend the money on the bigger cells instead. At 190amp and Max 14.6v output from the alternator, I can never overcharge 280ah cells, right? And as long as I never run the winch or starter motor for 10 mins straight I can't see over discharge being a problem. No sub zero or +50°c temps to deal with. If we take care of cell balancing some other way, what else is the BMS doing for me? I will probably have a separate volts/current/temp display somewhere, and a manual isolator switch in easy reach in case things go pear shaped.
3.1) I also can't see how the BMS cutting the battery in/out with the engine running and potentially high current loads would be doing any good for to electrical system. This car has a million computers all talking to each other and are quite complicated to work on. Maybe this isn't relevant. Clearly I'm no electronics engineer.

Thanks for reading
 
I’m not sure a single LiFePo battery and any bms is up to the task of a likely 300A+ load of a winch.
 
A single 4s LiFePO4 battery with the usual 120 amp BMS is not a good fit for this situation.

I have a two cylinder on-board generator in my RV trailer. Other forum members have measured the starter surge to be over 200 amps. A V8 could be higher.

The winch would likely send the BMS into overload.

A set of four 4s batteries might work, but then you're talking about a stupid amount of money.
 
G'day mate, I'm in a similar situation for a crank and winch setup but under bonnet.
It's a tall ask for a single unit, that's why the one's we are used to at home come in pairs for this reason.
The 380a heltec seems a good fit for fet based, its got a decent overcurrent capacity. I think I'm going with this one.
 
First of all, I think you should be looking at Headway style cylindrical cells. The have between 5C and 10C discharge rates. Some of them have a small capacity (8-10Ah).

Take a look at these:

Yes their capacity is low, but depending on how much space you have, you could run them in parallel.

Second, for your use case, I would look at the beefier Contactor based BMSs, not FET based.
These can handle a few hundred amps. I think that QUCC makes some.
 
G'day mate, I'm in a similar situation for a crank and winch setup but under bonnet.
It's a tall ask for a single unit, that's why the one's we are used to at home come in pairs for this reason.
The 380a heltec seems a good fit for fet based, its got a decent overcurrent capacity. I think I'm going with this one.
It seems to fit the bill, I noticed that they can adjust the voltage to 3.75v, I’ve got a smart alternator that hits 15 volt on brake regeneration, so 3.65v doesn’t work for me

not good for the cells, but it’ll just have a shorter life.
 
1) Forget a FET Based BMS, you WILL require Relay Controlled BMS, you do not want to hammer a FET based BMS with such loading.
The Relay Controlling BMS still does everything as usual BUT the actual current never goes through the BMS it runs through teh Heavy Duty Relays which can take a lot more Abuses & High Amperages.

A SEPARATE PORT installation is preferred in such a scenario as well. This means the BMS controls a relay JUST FOR LOAD and have one line for that, Then it has a separate line controlled by another relay to control the charging input, this can operate concurrently or individually.

Charging a Lithium Based battery from a Vehicle Alternator is TRICKY at best as they are not designed for it. There are several solutions than to the Mariine Crowd but that is outside of my area of gemeral knowledge. A Regular Alternator will not only damage the LFP Batteries but could very likely also self-destruct as well (many do when folks don't know what they are into).
 
That’s good information Steve,

we have quite a few lithium cranking options available here in Australia, I believe they all use mosfets, but they are around 50ah-100ah.

marine system and vehicle non can bus connected 2nd alternator’s require a regulation device to control the alternator

I know on the VW from 2017, you can select lithium as the battery chem and capacity, but every vehicle is different

this 500ah relay bms with seperate ports, could do the job for winching

https://www.aliexpress.com/item/1005003274810002.html?spm=a2g0o.cart.0.0.51553c00IXONOy&mp=1

although the 3/4s is out of stock at the moment.
 
3) convince me I need a BMS at all. Why not spend the money on the bigger cells instead. At 190amp and Max 14.6v output from the alternator, I can never overcharge 280ah cells, right?
If you reach full charge on a LiFePo4 280 AH battery, continuing at 14.6 volts could severely overcharge it.

If you dialed the alternator's voltage regulator back to about 13.6 volts, or whatever the battery manufacturer lists as a recommended float voltage, you might be OK. You might often leave the battery at less than 100% charge, but that's OK. But asking the BMS to serve as a charge controller is not good practice.

I like the suggestion to use a relay-based BMS in your application.
 
Sorry for the late reply guys, crazy time of year!
Thanks for all the replies, it's given me lots to think about.

The heltec unit certainly looks good from a spec and price point but I agree a FET based solution doesn't seem ideal.

I have seen the lithium starting batteries but can't figure out how they've done it nor too many reviews on how they actually perform. They all seem to be 100ah max so I'd need 2 which is out of the budget at this time.

Given my constraints are more about space than weight I am thinking that my best bet might be to downgrade the current AGM H9 starting battery to something slightly smaller (N70ZZ or thereabouts) and pack the remaining space in the battery box with 4 x ~100ah prismatics and a simple 50a BMS for camping.
Keep the AGM for high current duties and use lifepo4's energy density to pack in extra AH for low current stuff. Seems like BMS technology needs a couple more years to mature.

I have to remove the seat to measure exactly how much room I have but this is a pic from Google. Maybe I can even fit 100ah of cylindrical cells and keep the H9.
images
 
Seems like BMS technology needs a couple more years to mature
I think the technology is fairly mature. The market, applications, and supply just need to mature. Beyond that it’s entirely possible LiFePo may be curling down to obsolete in five years. There’s a few new tech batteries ‘they’ are working on.
 
I'd drop two (or three) of these in parallel, they are specifically designed for jump starting. I don't have one of those models specifically, but I have multiple units from the same brand and company. They all work flawlessly.


Or go with a contactor (relay) based BMS as @Steve_S said. Either way, I don't think you're going to be able to use a regular BMS for your project.

As far as being worried if your battery pack can take it, I wouldn't worry. I made a jump box that can crank my ice-cold V8 4Runner out of four 25ah LiFePO4 cells. The 280's you are talking about shouldn't have any issue starting a car at 400+ amps briefly. Most cells I've delt with are 2-3c continuous discharge, and 5-10c pulse.

However, if the cells are looking at are only 2C pulse rated, check out some other cells.

I'll second @meetyg 's suggestion too. Those Headway cells from Battery Hookup are probably exactly what you are looking for. I would recommend their 25ah blue cells as well, they are rated to 5c continuous (some spec sheets recommend 3c, others state that the cells have been tested at 5c), and will push well over 10c. A 4s4p pack of those would be 100ah, with a 500 amp discharge, and ~1000a pulse. They are also small(ish) cells and can be configured into odd, and tightly fitting spaces.
 
I'd drop two (or three) of these in parallel, they are specifically designed for jump starting. I don't have one of those models specifically, but I have multiple units from the same brand and company. They all work flawlessly.


Or go with a contactor (relay) based BMS as @Steve_S said. Either way, I don't think you're going to be able to use a regular BMS for your project.

As far as being worried if your battery pack can take it, I wouldn't worry. I made a jump box that can crank my ice-cold V8 4Runner out of four 25ah LiFePO4 cells. The 280's you are talking about shouldn't have any issue starting a car at 400+ amps briefly. Most cells I've delt with are 2-3c continuous discharge, and 5-10c pulse.

However, if the cells are looking at are only 2C pulse rated, check out some other cells.

I'll second @meetyg 's suggestion too. Those Headway cells from Battery Hookup are probably exactly what you are looking for. I would recommend their 25ah blue cells as well, they are rated to 5c continuous (some spec sheets recommend 3c, others state that the cells have been tested at 5c), and will push well over 10c. A 4s4p pack of those would be 100ah, with a 500 amp discharge, and ~1000a pulse. They are also small(ish) cells and can be configured into odd, and tightly fitting spaces.
Looking closely, that's actually a JBD BMS!
Nice...
 
Hi guys I have been researching a lifepo4 setup for my 4x4 and all roads seem to lead to this forum so I'm here asking for some help as I am a little out of my depth.

My old 4x4 has a single 250ah deep cycle AGM which runs a fridge, camp lights and the radio for a few days at a time with plenty of reserve for starting the engine.

New 4x4 has no room for dual batteries, or such a big single unit. It comes factory with a H9 AGM under the driver's seat. 190a (smart?) alternator, gasoline V8 turbo, 1.7kw starter motor.

I am from Australia. The coldest we see is around 0°C in winter. So no drastically high or lows temps for the battery to deal with.

I would like to replace the under seat battery with 4 x 200-280ah lishen or eve lifepo4 cells but choosing a BMS has me going around in circles.

Starter should draw 1700/12 =140 amps for let's say 5 seconds on average, or 30 seconds at a time during a no-start scenario.

Winch (not yet fitted) will anecdotally draw 200-400 amps when loaded up. Only used for 30 seconds, then allowed to cool.

Inrush current for both should be 2-3 times the above for <1 second?

Most prismatic cells seem to be good for 1C continuous or 2C for upto 30 seconds. Seems like 200ah cells would be on the limit but the 280ah would give me some headroom while stretching the budget.


1) do I just slap a 250a Daly on it and not worry? Best option looks like a 600a Chargery setup, but spendy. Or the 300a Chargery, maybe borderline. Any other options I've missed?

2) how come none of the 200-300a 12v pre-built lifepo4 batteries for sale are rated for cranking? Seems like they would have enough C rating and borderline enough BMS.

3) convince me I need a BMS at all. Why not spend the money on the bigger cells instead. At 190amp and Max 14.6v output from the alternator, I can never overcharge 280ah cells, right? And as long as I never run the winch or starter motor for 10 mins straight I can't see over discharge being a problem. No sub zero or +50°c temps to deal with. If we take care of cell balancing some other way, what else is the BMS doing for me? I will probably have a separate volts/current/temp display somewhere, and a manual isolator switch in easy reach in case things go pear shaped.
3.1) I also can't see how the BMS cutting the battery in/out with the engine running and potentially high current loads would be doing any good for to electrical system. This car has a million computers all talking to each other and are quite complicated to work on. Maybe this isn't relevant. Clearly I'm no electronics engineer.

Thanks for reading
not sure if it has been mentioned but a few people are putting in supercapacitors for starting or assisting starting with a lithium battery 'behind' it. have a look on FB - one particular site is FPV-Power
 
Thanks for the input guys, really appreciate it. I have abandoned the idea of LIFEPO4 for cranking/winching for now. Maybe on another vehicle down the line. In this car i am going to try a hybrid AGM/LIFEPO4 setup:
 

The video shows winching currents typically seen are only 250a and seem to max out at 400a. He is using 2 75ah DCS lithium batteries in parallel and had no issues winching. Surely a 280ah battery could manage.
 
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