Lithium again...

Just done similar, knackered old lead acid start and 5 year old 2 x t105 out. One Ecoworthy 300Ah with blue tooth and new lead acid start. Alternator too lead acid , 30amp dc/dc victron ,20 amp mains charger on lithium , solar controller to lithium. Fuses fitted where req. Bukh 24 with starting handle in case lol. Not sure if a shunt will give any more useful information the the BMS on battery , however can add later.
Will disconnect any charging system when leaving for insurance purposes
Edit
Big weight saving a plus
 
wingcommander said:
Just done similar, knackered old lead acid start and 5 year old 2 x t105 out. One Ecoworthy 300Ah with blue tooth and new lead acid start. Alternator too lead acid , 30amp dc/dc victron ,20 amp mains charger on lithium , solar controller to lithium. Fuses fitted where req. Bukh 24 with starting handle in case lol. Not sure if a shunt will give any more useful information the the BMS on battery , however can add later.
Will disconnect any charging system when leaving for insurance purposes
Edit
Big weight saving a plus
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Sounds good.
The shunt will give you accurate SOC. You can't establish anything from voltage.
 
PaulRainbow said:
Out of interest, why ?
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It doesn't seem a good idea to me to put two different chemistries, at different voltages, in parallel, as the lithium will try to charge the lead.
Perhaps it would be ok, I just worry about what sort of current would flow between them and whether the system was able to work with that without blowing any fuses etc.
I know that a hybrid system is in permanent parallel. It's entirely possible that I'm being over cautious.
 
Sea Change said:
It doesn't seem a good idea to me to put two different chemistries, at different voltages, in parallel, as the lithium will try to charge the lead.
Perhaps it would be ok, I just worry about what sort of current would flow between them and whether the system was able to work with that without blowing any fuses etc.
I know that a hybrid system is in permanent parallel. It's entirely possible that I'm being over cautious.
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A lot has been said online about different chemistries and voltages etc, but the bulk and float voltages of Lithium are well within the acceptable range for LA batteries. For instance, at 90% SOC LFP is 13.4V, which is exactly where i would set the float voltage for LA. All the way down to 30-40% they get down to about 13V, below the float voltage of LA, so it doesn't matter if they are held at anything between 90% and 30%, they won't be too high, perhaps a touch lower than ideal at lower SOC.

I ran mine with LA and LFP in parallel for a year to test what happened, nothing untoward did. But, with the alternators connected to the LA little charge went to the LFP, it works far better with a DC-DC charger from the actual engine batteries to the LFP. I also had concerns of how things would go in the event of failures, for instance, what would happen if the LA battery had a shorted cell ?

I concluded that whilst it didn't signal the end of life as we know it, a better system would be to use a DC-DC charger between the engine and LFP batteries (better charging) and leave the LA for the engine batteries (probably safer in failure modes. For emergency situations the parallel switch/solenoid and, if needed, a BMS bypass switch/solenoid was safe enough, as long as it was done in such a way as to minimise the chances of either/both being left on accidentally.

My own system has key switch operated solenoids (as does the original battery isolators), with bright red LED warning lights to indicate they are on. The keys can be left out to stop accidental activation as an extra safeguard.
 
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Our Fogstar BMS shunt matches the Victron exactly and always has. So much so I almost never use the Bluetooth any more. If money was an issue I wouldn’t fit an external shunt.
 
PaulRainbow said:
That would be unusual, it's normally read from the BMS, which isn't a shunt, it's just a coulomb counter.
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I find that if you regularly get the battery to float, like every day or two, the inbuilt bms SOC reading is OK. If you go for a week without getting the battery fully charged and you have had some big loads applied, the BMS SOC can be a long way out compared to a proper shunt.
 
geem said:
I find that if you regularly get the battery to float, like every day or two, the inbuilt bms SOC reading is OK. If you go for a week without getting the battery fully charged and you have had some big loads applied, the BMS SOC can be a long way out compared to a proper shunt.
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Exactly that for me too, i've even seen the BMS SOC reading zero.
 
PaulRainbow said:
That would be unusual, it's normally read from the BMS, which isn't a shunt, it's just a coulomb counter.
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Fogstar (the manufacturer) call it a shunt.

Edit: bit of reading later, yes there is a shunt in there, as is there in the Victron. Both use their shunt to measure current then the coulomb counter is the bit that monitors usage over time. Effectively identical systems.
 
lustyd said:
Fogstar (the manufacturer) call it a shunt.

Edit: bit of reading later, yes there is a shunt in there, as is there in the Victron. Both use their shunt to measure current then the coulomb counter is the bit that monitors usage over time. Effectively identical systems.
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I'll stand corrected then. If the battery has a genuine shunt that all of the current passes through, then it should give an accurate reading.
 
Sea Change said:
I'll stand corrected then. If the battery has a genuine shunt that all of the current passes through, then it should give an accurate reading.
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The blurb from Fogstar explains that its not a true shunt. It explains how to reset to 100% by fully charging. Its just the same as our JK BMS. This is why thr Victron Smart shunt is a good addition.
The smart shunt should also be connected to the Victron MPPT vis Bluetooth such that it gets an accurate voltage reading direct from the battery terminals. This ensures that the MPPT knows the true battery voltage, not the voltage is measures at its own battery wire terminal. Especially useful if your MPPT is some distance away from the battery
 
The main difference seems to be that it can't measure very low currents, but it is still a shunt and works in the same way. Our boat rarely has such low current flow, and I'm not sure many boats would drop that low for long enough to be an issue these days. The internal shunt is certainly good enough, but obviously doesn't integrate with anything so I think a Victron is a reasonable investment
 
lustyd said:
The main difference seems to be that it can't measure very low currents, but it is still a shunt and works in the same way. Our boat rarely has such low current flow, and I'm not sure many boats would drop that low for long enough to be an issue these days. The internal shunt is certainly good enough, but obviously doesn't integrate with anything so I think a Victron is a reasonable investment
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They also don't measure high currents accurately. If we do plenty of electric cooking, the JK inbuilt SOC will under read. The Victron Smart shunt will tell us we have actually discharged to a lower SOC
 
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