Quote:
Originally Posted by s/v Jedi
No, you don’t charge your lithium bank with the alternator. You charge the lithium bank with the dc-dc converter.
That said, if your alternator can overheat with the added 40A load from the dc-dc charger then yes, it becomes a mickey mouse system. There should never be a manual action required to prevent overheating because it is a recipe for disaster. |
And thats exactly the problem with DC2DC chargers that they don't protect the alternator as nobody on the hottest day of the year actually limits the current on his
installation in different RPMs. and then figure out which limitation on current in his
installation is save means the alternator stays below the temp his/her alternator can withstand. i would assume that 99% don't even know what that temp acctually is on their alternator.
99% incl. professional installers just take 50% of the rating of the alternator as limiting current and they think all is ok but is that really ok??
99% have no glue as they don't mount a temp probe on their alternator and
monitor the temps and thats why i said i would have expected from a victron DC2DC that when newly developed and a whooping
price of 460Euro like the 50A it has a temp probe that goes on alternator so the DC2DC finally knows when eg automatically switch to 50% output to really protect the alternator. But victron failed as they meanwhile turn into another lemon squeezing company and their aim was just to produce the same thing cheaper and less of an
heater but not safer.
And the DC2DC is advertised and recommend from highly regarded installers and even installed by french mass manufacturer now on totally dumb old alternator means they only have a regulator but no temp sensor.
Means a huge part of installations out there is a micky mouse installation due to Jedi. And i agree, thats why i said below 70A alternator a DC2DC makes also no sense financially as modifing the alternator and regulate it externally with temp protection cost the same then a DC2DC but is not protecting it.
Below that 70A threshold using a DC2DC with 50%
rule is fine as thats mainly small
boats with small energy needs plus the alternator is so
cheap then in the rare case when it goes up in smoke you just buy a new or used like newhaul for 30 bucks and if you have a renogy DC2DC you just charge it from now on with 50%.
There are some case with big dumb alternators like Simi with his
power boat that after you observe the alternators temp over a longer periode with temp probes and then get DC2DC like the 60A renogy or sterling to limit the current when you install lithium as this is much simpler and economical to install then installing eg new
cables etc. For external regulation.
Where a DC2DC really make sense is what Jedi is doing in his own installation when your alternators are 12V but your lifepo4 house is 24V or 48V and your alternator is just a backup charge source and should simply be safe operating and not go up in smoke.
But the majority of the cases on newer vessels if the alternator has a proper working internal temp regulation it protects itself and a DC2DC is just a waste of money as not needed at all to protect the alternator as the alternator does that himself. Additionally it limits the output unnecessarily as what the alternator can deliver depends only on the internal temp of it which the DC2DC don't know and limits the current when its absolutely not necessary.
Then you have 2 possible installations:
A) write Nordkyn design if your alternator can be steered by Nordkyn VSR200 modul which without modification turns it into a fully regulated one, chance is very high it does. Its around 300 to 350Euro depending on VAT and
shipping location. You get a surge protector and say goodbye for good to the dread lead chemistry also as starter.
B) you use an splitting diode with your lead or LTO starter. Charging a lifepo4 works with every lead regulator and in 95% of the case the alternator with internal temp protection has an
agm charge profile and goes not above 14.5V. The you take Victron ArgoFET and the
AGM or LTO is always there when BMS or a BMV shuts of the charge with a contactor because Lifepo4 is full ( best at SOC 95-98% and let solar do the rest).
If you have the rare case that the temp protected alternator has a FLA regulator that goes up to 15V then take an Argodiode that with its voltage drop brings the voltage down to 14.6V instead 15V, rest like above.
Then you use a small 5 or 10A DC2DC from Lifepo4 to lead start to keep it in float or who is smart actually uses a small MPPT or even a
cheap PWR does it with a 50W panel which you can mount on any vessel and float the starter like this. Or even more smart and use an LTO as starter which needs no floating at all and no charger at all to keep it charged and in the very rare case you need to recharge it without running the motor simply parallel it to lifepo4 with the selector switch
And that a BMS can switch off a source to optimize charging or discharging a lot can meanwhile do and there is nothing wrong about that, if you are a purist like Jedi use a battery
monitor, which should be on the Lifepo4 anyhow, to shut it off the charge from alternator when lifepo4 house is full.
Linear Mode
Recent Discussions