LiFePo battery upgrade question

Some folks say it is best to add a dc to DC converter to prevent the alternator from overloading.

Depending on the alternator output, the answer is yes. For high output alternators you need a DC - DC convertor or a Victron Cyrix-li-ct.

pianotuna wrote:
Some folks say it is best to add a dc to DC converter to prevent the alternator from overloading.

I wasnt in this camp at forst but them more I read and think about it it makes sence. a altanator is optimized for a starting battery where most of us have some sorty of deep cycle batteries in our rv's the DC to DC charger will let you optomize the carge profiles for your house batteries while letting the altanator take care of your truck starting battery. this is my thought anyways, am I missing anything?

Steve

StirCrazy wrote:

pianotuna wrote:
Some folks say it is best to add a dc to DC converter to prevent the alternator from overloading.

I wasnt in this camp at forst but them more I read and think about it it makes sence. a altanator is optimized for a starting battery where most of us have some sorty of deep cycle batteries in our rv's the DC to DC charger will let you optomize the carge profiles for your house batteries while letting the altanator take care of your truck starting battery. this is my thought anyways, am I missing anything?

Steve

I have a 30' Airstream Land Yacht with the 7.4 Vortec motor. Any idea what size alternator it has and if it needs a DC to DC converter?

Teleman wrote:
I have a 30' Airstream Land Yacht with the 7.4 Vortec motor. Any idea what size alternator it has and if it needs a DC to DC converter?

Since you have a trailer the alternator charging will generally not be an issue. The long charge wire and multiple connections will self regulate the current to be below the 30-40 amp fuse rating.

Teleman wrote:
I ordered a 200AH LifePo battery to replace my two 100AH lead acid batteries and also a compatabile converter which takes care of charging the battery with shore or generator power but what about charging the battery with the alternator? Does the battery's BMS take care of everything and therefore no need to change or upgrade the alternator? Sorry if this is a dumb question!

Since I do not charge from the vehicle, I can only provide you with an estimate…I too have a single 200a/h LFP, but the overwhelming majority of charging is provided by 440w of solar harvest…Having said that, the most shore power amperage I’ve ever witnessed the single battery to take (using an onboard100ainverter-charger) is between 65-70amps with a tapering down trend as voltage slowly begins to rise.

So my best advice is that IF this amperage represents about 25% of your alternator’s capacity (roughly speaking) your probably not going to have an issue, but in the end, the length and AWG size of your alt-to-batt charge wire may in fact be the real limiting factor…If you have a ‘smart batt’ (with bluetooth) or a decent shunt based SOC battery meter to monitor current, the best way to know may be to first try out what you have to determine the results…

3 tons

time2roll wrote:

Teleman wrote:
I have a 30' Airstream Land Yacht with the 7.4 Vortec motor. Any idea what size alternator it has and if it needs a DC to DC converter?

Since you have a trailer the alternator charging will generally not be an issue. The long charge wire and multiple connections will self regulate the current to be below the 30-40 amp fuse rating.

I'm sorry it's a Class A motorhome. I should have specified, though I did mention the Vortec motor.

3 tons wrote:

Teleman wrote:
I ordered a 200AH LifePo battery to replace my two 100AH lead acid batteries and also a compatabile converter which takes care of charging the battery with shore or generator power but what about charging the battery with the alternator? Does the battery's BMS take care of everything and therefore no need to change or upgrade the alternator? Sorry if this is a dumb question!

Since I do not charge from the vehicle, I can only provide you with an estimate…I too have a single 200a/h LFP, but the overwhelming majority of charging is provided by 440w of solar harvest…Having said that, the most shore power amperage I’ve ever witnessed the single battery to take (using an onboard100ainverter-charger) is between 65-70amps with a tapering down trend as voltage slowly begins to rise.

So my best advice is that IF this amperage represents about 25% of your alternator’s capacity (roughly speaking) your probably not going to have an issue, but in the end, the length and AWG size of your alt-to-batt charge wire may in fact be the real limiting factor…If you have a ‘smart batt’ (with bluetooth) or a decent shunt based SOC battery meter to monitor current, the best way to know may be to first try out what you have to determine the results…

3 tons

I have a Victron Smart Shunt. What should I look for?

Teleman wrote:

time2roll wrote:

Teleman wrote:
I have a 30' Airstream Land Yacht with the 7.4 Vortec motor. Any idea what size alternator it has and if it needs a DC to DC converter?

Since you have a trailer the alternator charging will generally not be an issue. The long charge wire and multiple connections will self regulate the current to be below the 30-40 amp fuse rating.

I'm sorry it's a Class A motorhome. I should have specified, though I did mention the Vortec motor.

Most people who don't own an Airstream are unaware that Airstream makes/made motorhomes.

Current production: https://www.airstream.com/touring-coaches/

Teleman wrote:

time2roll wrote:

Teleman wrote:
I have a 30' Airstream Land Yacht with the 7.4 Vortec motor. Any idea what size alternator it has and if it needs a DC to DC converter?

Since you have a trailer the alternator charging will generally not be an issue. The long charge wire and multiple connections will self regulate the current to be below the 30-40 amp fuse rating.

I'm sorry it's a Class A motorhome. I should have specified, though I did mention the Vortec motor.

LOL. In this case I recommend a clamp-on DC meter to measure the current. Also verify the fuse rating if any. Worst case you can disconnect the charging connection until you get this sorted out.

You may have a BIRD to maintain charge on chassis and house batteries depending on the power source. The DC-DC charger will create a one way circuit and effectively disable half the function of the relay. Some MH have other control and bypass systems that should be reviewed for loss of functionality by adding a DC-DC charger. I would always be inclined to keep the OEM system if possible.