works DC-to-DC charging of Lifepo4 with a dead or a nearly dead FLA

[CaptainRivet]

Hi Lithium freaks
did anyone tried

1) if the DC-to-DC charging still works when the FLA starter is dead or nearly dead (won't cranck the engine) but engine runs.

2) if its dead due to eg heavy sulfaltion the cells are accctually shorted so low resitance. So is the dead low resistance FLA still a high enough resistance for the standard alternator to work properly and not fry the alt?


Never thought about these sceanrios and have no dead one to test...

[smac999]

dc to dc is normally going to be voltage triggered. if the engine is running and charging the engine battery and you get the start battery back up to 13v it will turn back on. it may have a delay to let the engine battery charge first.

if the engine battery is dying it may because the dc to dc is not voltage or ignition triggered and it's constantly draining the engine battery into the house. which is really bad

[CaptainRivet]

Originally Posted by smac999

dc to dc is normally going to be voltage triggered. if the engine is running and charging the engine battery and you get the start battery back up to 13v it will turn back on. it may have a delay to let the engine battery charge first.

if the engine battery is dying it may because the dc to dc is not voltage or ignition triggered and it's constantly draining the engine battery into the house. which is really bad

Ignition triggered and engine runs but LFA nearly dead means it won't be up to 13V anymore is the DC to Dc charger working and charging lifepo4 or not.

Why its dead doesn't matter (and
It will die with a LFA all 5-7years, sometimes earlier) question is if its dead can I
1)charge the lifepo4 via DC to DC and alternator
2) while charging can I damage or fry it because LFA has low resistance due to shorted cells

[goboatingnow]

As I’ve repeated endlessly. The best solution , not the most technical convenient, is to put in proper control units to charge the LFP domestics. Then indirectly charge the starter via a relatively low cost low power dc dc converter.

This means you have several advantages. If you loose your alternator you can recharge from the LFP, or even start from the LFP , You can loose your starter battery and still start your engine.

It’s also the most electrically efficient. Varies control strategies can be deployed to determine when the dc dc converter kicks in.

If yiu have a damaged LFP. The nature of these situations , is you’ll be taking the LFP off line. It’s not advisable to struggle on with a seriously damaged LFP.

You can arrange your wiring to allow you to reconfigure so that the alternator could bypass the failed LFP. but how sophisticated this is is a function of your risk management perspective.

[CaptainRivet]

Originally Posted by goboatingnow

As I’ve repeated endlessly. The best solution , not the most technical convenient, is to put in proper control units to charge the LFP domestics. Then indirectly charge the starter via a relatively low cost low power dc dc converter.

This means you have several advantages. If you loose your alternator you can recharge from the LFP, or even start from the LFP , You can loose your starter battery and still start your engine.

It’s also the most electrically efficient. Varies control strategies can be deployed to determine when the dc dc converter kicks in.

If yiu have a damaged LFP. The nature of these situations , is you’ll be taking the LFP off line. It’s not advisable to struggle on with a seriously damaged LFP.

You can arrange your wiring to allow you to reconfigure so that the alternator could bypass the failed LFP. but how sophisticated this is is a function of your risk management perspective.

I am aware of that but it does not answer my questions.
Would need external regulators for both engines, a lot off money again.. And if i have that then i would delete a starter for one engine completely hrving a LifePo4 as starter house and get a LTO starter for the other thats charged via DC to Dc from LFP. Thats what i will do in the long run....

[guyrj33]

Originally Posted by CaptainRivet

Hi Lithium freaks
did anyone tried

1) if the DC-to-DC charging still works when the FLA starter is dead or nearly dead (won't cranck the engine) but engine runs.

2) if its dead due to eg heavy sulfaltion the cells are accctually shorted so low resitance. So is the dead low resistance FLA still a high enough resistance for the standard alternator to work properly and not fry the alt?


Never thought about these sceanrios and have no dead one to test...

Let's all keep in mind this is a hypothetical question.

[CaptainRivet]

Originally Posted by guyrj33

Let's all keep in mind this is a hypothetical question.

That is not hypothetical. I had more then one completely dead or desulfated battery. Ito a question of operational security.
And at the moment 2 DC to DC charger charge my LifePo4 house via LFA starter...
If LFA starter is dead and it doesn't work i cannot charge my LifePo4.
If LFA starter is shorted out due to eg desulfatation (regulator faulty and boiled LFA withou me noticing) and its not the the high resistant load anymore that protects, I fry the new alternator...

[Statistical]

Originally Posted by CaptainRivet

That is not hypothetical. I had more then one completely dead or desulfated battery. Ito a question of operational security.
And at the moment 2 DC to DC charger charge my LifePo4 house via LFA starter...
If LFA starter is dead and it doesn't work i cannot charge my LifePo4.
If LFA starter is shorted out due to eg desulfatation (regulator faulty and boiled LFA withou me noticing) and its not the the high resistant load anymore that protects, I fry the new alternator...

I have never understood the desire to connect alternator the starter battery and then try to use DC to DC to charge the much larger higher energy use house bank.

You don't really need the starter battery to start the engine a decent LFP pack can start the engine too. The starter battery is simply the backup. If it helps call it the backup instead of starter battery.

Alternator to large house bank. Small DC to DC charger to top off the starter battery.

Starter motors tend to use 100A to 300A so 1.2 to 3.6 kW and start in less than 30 seconds. So even at the high end 3,600 W / 60 / 60 * 30 = 30 Wh or at 12V ~ 10Ah. That is what it takes to start up an engine and since engine likely uses less and starts faster in reality it is much less than that. Even the tiniest DC charger can recover that quickly and the LFP pack can take the full output of your alternator.

[guyrj33]

Originally Posted by CaptainRivet

That is not hypothetical. I had more then one completely dead or desulfated battery. Ito a question of operational security.
And at the moment 2 DC to DC charger charge my LifePo4 house via LFA starter...
If LFA starter is dead and it doesn't work i cannot charge my LifePo4.
If LFA starter is shorted out due to eg desulfatation (regulator faulty and boiled LFA withou me noticing) and its not the the high resistant load anymore that protects, I fry the new alternator...

you wrote

Never thought about these sceanrios and have no dead one to test...

So, yes this is hypothetical.

Also I think you mean to ask about a sulfated battery.

The answers to your questions can be best answered by your equipment manufacturer or by the owners manual.

[kmacdonald]

It's potentially less expensive to connect alternator to LA battery. B to B charger for $200
Alternator to LFP: $300 charge controller, $500+ externally regulated alternator, $100 alternator protection device.

[CaptainRivet]

Originally Posted by kmacdonald

It's potentially less expensive to connect alternator to LA battery. B to B charger for $200
Alternator to LFP: $300 charge controller, $500+ externally regulated alternator, $100 alternator protection device.

Not even money, yes a bit....
The key is ease of install. I have a cat, STB hull has already a FLA starter +house and the BB a FLA starter thats paralleled to the STB battery as soon as one of she engines run and alternators run. Both engines are new, so alternator too.
I simply throw 2 of the 4 LFA in STB out and connect 2x 30A Victron Dc to DC charger to it. So doesn't matter which engines run i have 60A charge, max one alternator can do anyhow. Only use some charge current when both engines run, very seldom. No other change to make.
Alternator is backup charge source anyhow, it just has to work when engine runs. Main is 120A solar charge....