Change to LifePO4 - Emergency engine starting ?

PaulRainbow said:
To start a pair of 7 litre diesels ?
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Something like this would bring it to life in seconds even with no battery attached at all.

https://hgvdirect.co.uk/heavy-duty-li-polymer-booster-pack-12v-24v-2500-amp-guardian-jp6.html

Your current batteries won’t be putting out 2500A or anything even close to it.

I have started a v8 truck engine at 24V before by simply putting a little tiny NOCO 12V boost pack on one of the (flat) batteries.

The challenge is the 24V ones tend to be much bigger / more expensive than the 12V ones.
 
jakew009 said:
Something like this would bring it to life in seconds even with no battery attached at all.

https://hgvdirect.co.uk/heavy-duty-li-polymer-booster-pack-12v-24v-2500-amp-guardian-jp6.html

Your current batteries won’t be putting out 2500A or anything even close to it.

I have started a v8 truck engine at 24V before by simply putting a little tiny NOCO 12V boost pack on one of the (flat) batteries.

The challenge is the 24V ones tend to be much bigger / more expensive than the 12V ones.
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Yes, in the event of the LFPs not being able to start the engines that would be one possible solution.
 
I have a 6lt diesel and my 710 Ah (19kWh) lithiums start it in an instant. I’m certain a much smaller battery such as yours would murder the job. The trick will be in by-passing the BMS current limit. You may need some dedicated starter wiring for just this job. I can do this as I have a BMS with no current limit function and I rely on fuses.

As another reference, motorcycle lithium batteries are really tiny. A 50Wh battery will start a 1200cc petrol engine reliably.so 6 times that is 300Wh to pro-rate to a 7lt engine. You have nearly ten times that in battery power. Does a diesel take 10X the starting power of a like for like sized petrol engine? I doubt it.
 
Zing said:
I have a 6lt diesel and my 710 Ah (19kWh) lithiums start it in an instant. I’m certain a much smaller battery such as yours would murder the job. The trick will be in by-passing the BMS current limit. You may need some dedicated starter wiring for just this job. I can do this as I have a BMS with no current limit function and I rely on fuses.

As another reference, motorcycle lithium batteries are really tiny. A 50Wh battery will start a 1200cc petrol engine reliably.so 6 times that is 300Wh to pro-rate to a 7lt engine. You have nearly ten times that in battery power. Does a diesel take 10X the starting power of a like for like sized petrol engine? I doubt it.
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You're confusing energy storage with power.
 
Zing said:
Correct!
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I know it's correct, but it has no relevance to post #1. Storage capacity is not the issue, it's getting sufficient amps to the starter motors, particularly during the second the starter button is pressed when the inrush is greatest.
 
PaulRainbow said:
I know it's correct, but it has no relevance to post #1. Storage capacity is not the issue, it's getting sufficient amps to the starter motors, particularly during the second the starter button is pressed when the inrush is greatest.
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He's trying to say that LFP batteries are rated at say 0.5C continuous, 1C max / 2C pulse.

So a 3584Wh 12.8V battery with a 1C rating can discharge at 280A.

Obviously as the battery gets smaller, the max amperage also decreases. It's not quite true because smaller batteries tend to have higher C ratings in the first place up to say 10C.
 
jakew009 said:
He's trying to say that LFP batteries are rated at say 0.5C continuous, 1C max / 2C pulse.

So a 3584Wh 12.8V battery with a 1C rating can discharge at 280A.

Obviously as the battery gets smaller, the max amperage also decreases. It's not quite true because smaller batteries tend to have higher C ratings in the first place up to say 10C.
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Oh, i said the in 10 words in post #6 🤣
 
PaulRainbow said:
I know it's correct, but it has no relevance to post #1. Storage capacity is not the issue, it's getting sufficient amps to the starter motors, particularly during the second the starter button is pressed when the inrush is greatest.
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Storage capacity absolutely is the issue as regards cranking amps. See post #65 and #63. 🤣🤣
 
Zing said:
Storage capacity absolutely is the issue as regards cranking amps. See post #65 and #63. 🤣🤣
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Why do i want to refer back to your previous posts when they are largely irrelevant ?

It's all well and good having plenty of stored energy, but if you can't get it to where it needs to be it is useless.

I have, for instance, 280Ah of LFP @24V, that's 560Ah @12V, more than enough stored energy to start my engines and more than enough for anything else on my boat, but the availability of power is limited by the BMS, wiring, fuses etc.

In your case, with you poorly designed installation, your BMS doesn't protect from excessive load, that's done by fuses, so you overload the system and a fuse blows, now you don't have any power and you have to go and change a fuse. That's an incredibly bad way of doing things with LFP.
 
jakew009 said:
He's trying to say that LFP batteries are rated at say 0.5C continuous, 1C max / 2C pulse.

So a 3584Wh 12.8V battery with a 1C rating can discharge at 280A.
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That's incorrect. The 1C rating is only what the manufacturer quotes as relating to the max cycles of the cells. IE, 8,000 cycles @ x DOD and xC. The battery is capable of discharging many more amps than that if it's not protected by a BMS.
jakew009 said:
Obviously as the battery gets smaller, the max amperage also decreases. It's not quite true because smaller batteries tend to have higher C ratings in the first place up to say 10C.
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PaulRainbow said:
That's incorrect. The 1C rating is only what the manufacturer quotes as relating to the max cycles of the cells. IE, 8,000 cycles @ x DOD and xC. The battery is capable of discharging many more amps than that if it's not protected by a BMS.
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mmmmm

That doesn't agree with general battery info that I know and read about ..

The C rating (discharge) :

C x capacity in AH = Max Amps that battery can theoretically provide.

C rating is also quoted for charge - but that uses a different calculation and often is just stated as 0.5C .. 1C or an Amp figure.

I make this discharge calculation every new model setup (size of packs makes no difference - the formula stands).
 
Refueler said:
mmmmm

That doesn't agree with general battery info that I know and read about ..

The C rating (discharge) :

C x capacity in AH = Max Amps that battery can theoretically provide.

C rating is also quoted for charge - but that uses a different calculation and often is just stated as 0.5C .. 1C or an Amp figure.

I make this discharge calculation every new model setup (size of packs makes no difference - the formula stands).
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What Paul said is correct. They can deliver far more than their C rating amps. I have tested them when building liquid cooled batteries at 10C. These were Winston lifepo4 cells that have a factory rating of 3C discharge anyway. The only limiting factor on whether it reduces their life expectancy is the temperature gradient you create across the cell by running them at such high amps. This is why in cars they cool the cells, often using the cars AC system
 
geem said:
What Paul said is correct. They can deliver far more than their C rating amps. I have tested them when building liquid cooled batteries at 10C. These were Winston lifepo4 cells that have a factory rating of 3C discharge anyway. The only limiting factor on whether it reduces their life expectancy is the temperature gradient you create across the cell by running them at such high amps. This is why in cars they cool the cells, often using the cars AC system
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A bit of research suggests that EVE280Ah cells can sustain 10C for less than 1s without damage with good busbars and cooling. 3C for up to 30s is also no problem
 
geem said:
What Paul said is correct. They can deliver far more than their C rating amps. I have tested them when building liquid cooled batteries at 10C. These were Winston lifepo4 cells that have a factory rating of 3C discharge anyway. The only limiting factor on whether it reduces their life expectancy is the temperature gradient you create across the cell by running them at such high amps. This is why in cars they cool the cells, often using the cars AC system
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The C x Capacity calculation is for sustained demand ... and is fact.

What you and Paul are talking about is limited time BURST demand. All batterys can survive a limited burst demand ... in fact many Lithium will quote both C rate and Burst rates ...
Your post #77 actually confirms what I say .. BURST RATE.
 
Refueler said:
The C x Capacity calculation is for sustained demand ... and is fact.
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You didn't say that in post #75

You said "C x capacity in AH = Max Amps that battery can theoretically provide."

There isn't a set in stone formula for LFP anyway, ie, it isn't 1C discharge and 0.5 for charge for every make of cell, it's what the manufacturer has determined to be the most appropriate for safety, longevity etc
 
PaulRainbow said:
Why do i want to refer back to your previous posts when they are largely irrelevant ?

It's all well and good having plenty of stored energy, but if you can't get it to where it needs to be it is useless.

I have, for instance, 280Ah of LFP @24V, that's 560Ah @12V, more than enough stored energy to start my engines and more than enough for anything else on my boat, but the availability of power is limited by the BMS, wiring, fuses etc.

In your case, with you poorly designed installation, your BMS doesn't protect from excessive load, that's done by fuses, so you overload the system and a fuse blows, now you don't have any power and you have to go and change a fuse. That's an incredibly bad way of doing things with LFP.
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Not irrelevant,but on point. Sorry it eluded you.

A small mod is all you need. I’m sure it’s within your abilities. Do you need help?

Mine only blows a fuse for one consumer. That’s not poorly designed at all. It is well designed. However your system of having a BMS shut you down is worse. Everything gets shut down at once. Now that’s a poor design. Did you do it? 🤣🤣 Poorly designed indeed.
 
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