noelex
Well-known member
Blue Sea list the IC of ANL fuses as slightly higher than MRBF fuses.
ANL: 6000A @ 32V DC
MRBF: 5000A @ 32V DC
Mega: 2000A @ 32V DC
T Class fuses have a much higher IC rating of 20000A @ 125V DC.
Drop in Lithium Batteries - the basics?
- Thread starter dgadee
- Start date
ANL: 6000A @ 32V DC
MRBF: 5000A @ 32V DC
Mega: 2000A @ 32V DC
T Class fuses have a much higher IC rating of 20000A @ 125V DC.
NickRobinson
Well-known member
Reading the thread and Kelpie's thoughts-
"Another option, which I've not tried, is to fit lithium in parallel with a lead acid battery. I'm not aware that anybody in the forum has tried this but it is quite a tempting idea.:
I'm experimenting doing just that, but camper based. I've 200w solar feeding the existing two elderly FLA batts and the new 100Ah Lifepo drop in all in parallel. I've fitted a very small blade fuse (15A) to the lithium as a safety net and they are working well together, The lithium is getting less than 14.6v, but that's supposed to be good for its life.
No engine connection yet but I have a bi-directional VSR to fit. Again I'll monitor current using a clamp meter and alternator temp and fit a conservative fuse too.
At least one Youtuber goes on the record to say that a B2B is 'probably not needed' for a small capacity, non-marine set up like mine.
BTW, the power profile is great. I'll never buy another lead acid 'leisure battery'
"Another option, which I've not tried, is to fit lithium in parallel with a lead acid battery. I'm not aware that anybody in the forum has tried this but it is quite a tempting idea.:
I'm experimenting doing just that, but camper based. I've 200w solar feeding the existing two elderly FLA batts and the new 100Ah Lifepo drop in all in parallel. I've fitted a very small blade fuse (15A) to the lithium as a safety net and they are working well together, The lithium is getting less than 14.6v, but that's supposed to be good for its life.
No engine connection yet but I have a bi-directional VSR to fit. Again I'll monitor current using a clamp meter and alternator temp and fit a conservative fuse too.
At least one Youtuber goes on the record to say that a B2B is 'probably not needed' for a small capacity, non-marine set up like mine.
BTW, the power profile is great. I'll never buy another lead acid 'leisure battery'
Poey50
Well-known member
Thanks. I stand corrected. The latest reminder not to rely on memory.
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Kelpie
Well-known member
From memory (uh oh!) different manufacturers seem to give different figures for the AIC of fuses even if they are supposedly made to the same standard.
They aren't always expressed for the same voltage either.
The other thing I've struggled to get a figure on is the real world maximum discharge current from LFP cells. The numbers you see are all over the place.
They aren't always expressed for the same voltage either.
The other thing I've struggled to get a figure on is the real world maximum discharge current from LFP cells. The numbers you see are all over the place.
Poey50
Well-known member
Yes, agreed!
dgadee
Well-known member
What make of batteries would you recommend?
B27
Well-known member
What's it actually worth when a youtuber goes on the record saying 'probably'?
I can't find any respectable battery vendors saying it's OK to connect a Lifepo4 to an alternator via something like a VSR. Can you?
How will you know when your elderly FLA batteries are no longer bringing anything to the party?
lustyd
Well-known member
It's not not OK, you just have to control the output and cut it off when the batteries are charged. That can be done but it's better done automatically by a relatively cheap box that can be configured to look after the battery with a charge profile.
The elderly FLA batteries only need bring resistance to the party, and they'll do that forever
Poey50
Well-known member
You might come to know about it if the elderly FLA battery developed an internal short and turned into a 10 volt battery. A nice full LFP in parallel will pump a lot of juice into the dying FLA to attempt to equalise and all that heat has to go somewhere. Stand well back!
B27
Well-known member
Actual measurement of the short circuit current of a 160Ah LiFePO4 cell topped out at 1060 A.
https://www.researchgate.net/figure...ithium-based-batteries-LiFePO_fig15_316171277
Quite small cells of other Lithium families have more 'interesting' short circuit behaviour.
NickRobinson
Well-known member
"You might come to know about it if the elderly FLA battery developed an internal short and turned into a 10 volt battery. A nice full LFP will pump a lot of juice into the dying FLA and all that heat has to go somewhere. Stand well back!"
Hence the conservative 15A fuse.
Hence the conservative 15A fuse.
B27
Well-known member
I believe this is known to happen with banks of LA batteries, one battery dies, the others dump energy into it.
PaulRainbow
Well-known member
The fuse will limit current, but not voltage. If the good cells are charged they might not draw a lot of current, but will still be held at 14.x volts. That's a lot of gassing and a loud bang.
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PaulRainbow
Well-known member
The good batteries will hold the dead on at 14.x volts, or thereabouts. This results in a lot of heat and a lot of gassing. A very dangerous scenario, if there is a spark, there is likely to be a load bang and chunks of battery/acid everywhere.
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B27
Well-known member
I've seen the aftermath of a little lead acid battery from a moped exploding.
Nasty!
noelex
Well-known member
Thanks for the link. Surprisingly that is not much different to a deep cycle lead acid battery.
For example, a Mastervolt 200 Ahr lead acid gel battery will deliver at least 1100 A for 30 seconds at minus 18° C (the SAE test).
I would have expected higher current from the lithium cell, especially as it looks like a quality Winston product.
B27
Well-known member
A lot of confusion comes from 'internal resistance' often being quoted as dV/dI not V/I.
The slope of the volts/amps graph at the point of interest.
The internal resistance is valid for small changes of volts and amps.
It's wrong to extrapolate it outside of the working range.
For some devices, dV/dI can be negative. But only over a certain range.
The cold-cranking tests are not short circuit, they are the current to bring the volts down to something like 1.2V per cell. If you actually short circuit a battery fully, you may have bits of it in the ceiling before 30 seconds is up. Luckily it's pretty difficult to make a ten thousand amp short circuit.
Pete7
Well-known member
We have 220Ah LFP and 85Ah FLA in parallel as a house bank. charged from the SLA engine start battery via a Victron DC>DC 30A charger.
However, for Dgadee with a 140A alternator a 60A Sterling DC>DC might be better.
Kelpie
Well-known member
Not in any way my area of expertise, but wouldn't it be better to fit a regulator to protect the alternator, rather than a DC-DC charger? My little 18A Orion gets incredibly hot, surely that means a loss of be efficiency?
PaulRainbow
Well-known member
Better ? Most likely, but it's a more expensive option. You need a decent alternator for a start, something like a Balmar, then you need a good regulator, neither comes cheap. If you have a standard V belt driving the alternator it's not going to be up to the job of churning out lots of amps, you'll likely need to upgrade the pulley system and belts to a multi-vee arrangement.
That can add up to a sizeable amount. But, rather then being limited to the max current of a B2B you could have 100a plus from the alternator. That assumes one needs to get lots of charging from the alternator, a large solar array often negates the need.
