To charge or not to charge

[SEMPERAVANTI41]

I have converted my house batteries to 600 ah of Lithium, and they are working well. The Li batteries are either charged from the AC (Cristec) charger or from a Renergy 60 amp 12 v to 12 v charger connected to my start battery. The Renology charger is set to Lithium charging at 14.6 v (recommended charging v), while the Cristec charger is set to a maximum voltage of 14.4 v.. The Renergy charger is wired to only operate when the engine driven alternator is producing voltage. I could also wire the Renergy charger to operate when the Cristec charger is producing voltage. Would this be a good idea?

 

[Davidasailor26]

I wouldn’t set up the DC-DC to charge the house bank when the shore charger is on. I don’t know your Cristec output and whether it’s one bank or two, but either way I don’t think any good can come from having the DC-DC come on when the shore charger is.

If the shore charger is one bank then the DC-DC will be trying to charge the house bank from a start battery that itself isn’t being charged. That will quickly deplete the start bank.

If the Cristec is wired to both banks then when the DC-DC comes on it will present an extra load on the start bank side of the Cristec, so it will output more on that side, reducing the amount available to the house side. The DC-DC will have some amount of inefficiency, so some percentage of the current that the Cristec puts into the start bank be wasted rather than put into the house bank.

 

[mermike]

Where did the recommended charging voltage of 14.6V come from? That's pretty high for most LFP batteries. Most look for 14.1v or thereabouts. Battleborn is the only one that's in that range, at 14.5V.

 

[Maine Sail]

Where did the recommended charging voltage of 14.6V come from? That's pretty high for most LFP batteries. Most look for 14.1v or thereabouts. Battleborn is the only one that's in that range, at 14.5V.

14.6V/3.65V per cell is the max charge voltage for the LFP chemistry. Charging at 14.6V leaves you zero leeway if a cell gets out of balance. Charge at the lowest voltage, just a tad over were balancing begins..

 

[dlochner]

Keep it simple.

Alternator to Start Battery.

AC Charger to LFP battery

DC-DC charger from Start to LFP.

The start battery should always be fully charged and the DC to DC charger should only charge the LFP batteries when the voltage at the start battery is high enough to indicate charging. This will prevent the DC-DC charger from draining the start battery into the LFP battery. When ever the engine is running the alternator will be providing current to the start battery at a voltage higher than resting which will allow the DC-DC charger to charge the LFP batteries while the engine is running.

 

[SEMPERAVANTI41]

Thanks for all of your responses. Couple of answers:
The Cristec charger has 3 independent outputs.
The DC to DC charger (Renergy) will only charge if the start battery voltage is sufficient.
The manufacturer of the lithium batteries (Kepworth) stated the 14.6 v. I will heed Maine Sail's advice and reduce the charging voltage.
This also means that there is no reason to use the DC-DC charger when the 110 v charger is operating.

 

[dlochner]

The Cristec charger has 3 independent outputs.

Check your manual for the fine print. Most (all?) multi-output chargers divide the available current between the outputs. Thus a 3 outlet 60amp charger will only put out 20 a per outlet when all three are connected or 60a to one outlet when only one outlet is connected.

If your batteries are in parallel, then only one outlet need be used to charge all the batteries in the bank.

 

[mermike]

The 14.6v in the manual is the maximum voltage the battery will take before it disconnects.

 

[artboas]

I have found that Cristec chargers were installed by boat builders owing to low cost. Once you start upgrading your battery system, you really should think of a long term charger / inverter solution.
The 3 outputs share the max output current of the unit.

 

[SEMPERAVANTI41]

When I stated 3 independent outputs of the Cristec charger, I meant that the 3 outputs were isolated. So one battery could not discharge another battery.