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LiFePO4 conversion

Feb 26, 2004
21,564
Catalina 34 224 Maple Bay, BC, Canada
I like your approach of separating the LIFEPO4 batteries from the alternator.
It's not something to like, it is a necessity. Why? Because when the BMS says the LP bank is full, it cuts it off immediately from charging sources. If you do that with an alternator, you blow the diodes.
 

Tim22

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Jun 16, 2014
237
Hunter 310 Ottawa
Is 200 W a good match for the 200AH of battery capacity ?
For the sailing we do the 200W Solar with the 200ah is ok. Mostly we are in a slip with shore power so can charge with that. When we are away from the slip the solar won’t keep up but it will be enough to stay out for 4 or five days which is also about the limit for our holding tank! Our sailing area is the Ottawa river so it’s impossible to get more than 25 miles from home base.

I have been experimenting this winter with an induction cooktop which has worked well in the shop running off the LiFePO4 and inverter. Sucks up a lot of power though. Mostly we use the barbecue for cooking and rarely use the propane stove. if I can find a place for another 100ah battery I will be tempted to try going without the propane stove.

Tim
 
Oct 30, 2013
18
Wauquiez Gladiateur Anacortes
It's not something to like, it is a necessity. Why? Because when the BMS says the LP bank is full, it cuts it off immediately from charging sources. If you do that with an alternator, you blow the diodes.
I meant as opposed to isolating it with a battery to battery charger.
 
Apr 5, 2009
1,433
Catalina '88 C30 tr/bs Oak Harbor, WA
It's not something to like, it is a necessity. Why? Because when the BMS says the LP bank is full, it cuts it off immediately from charging sources. If you do that with an alternator, you blow the diodes.
I would agree with this statement if it was restricted to systems that are only connected to LFP. If the charge is going through a combiner that is connected to AGM start and LFP house, if the LFP shuts down, the AGM is still taking the charge so no harm, no foul.
 
Feb 6, 1998
11,361
Canadian Sailcraft 36T Casco Bay, ME
Most combiner / ACR's are the wrong voltage for LFP. For a stock alternator a DC to DC charger, at about half the rating of the stock alternator, is typically easiest. The B2B is sized at roughly half so you don't burn out the alternator..

For an alternator with external regulation a simple option is this:

 
Feb 26, 2004
21,564
Catalina 34 224 Maple Bay, BC, Canada
I would agree with this statement if it was restricted to systems that are only connected to LFP. If the charge is going through a combiner that is connected to AGM start and LFP house, if the LFP shuts down, the AGM is still taking the charge so no harm, no foul.
That's true.
Consider, however, Yandina's installation manual for their combiners:
"A better solution, in our opinion, is to connect the alternator
output to the house battery bank by connecting it to the load side
of the house battery switch. When the house bank rises to 13.1 V DC,
the Battery Combiner will close and allow the engine starting battery
to charge in parallel. "


Start banks are almost always full because it only takes a few ah to start an engine, even with glow plugs. Most of us, except the neanderthals in the UK, route the AO to the house bank, so the combiner is only moving current to the start bank AFTER the house bank's voltage rises enough to close the relay, meaning the house bank has had an opportunity to get some charge and is not depleted as much as when charging just begins.

Now consider an LP house bank with a relatively much smaller AGM or wet cell start bank. While the start bank's chemistry will absorb an LP shutoff of the AO, the combiner is now being tasked with carrying far higher currents, and, as such, the wiring between the combiner and the banks must be carefully sized to so accommodate this increased amperage. Yandina's manual suggests wire sizing that would lead me to believe they consider only AO>>house bank>>combiner>>start bank. The amperage going the other way, especially with LP that can absorb a lot higher charging currents than wet cells, should be considered when sizing this wire compared to Yandina's "Use 3’ (minimum) of 6 AWG wire to connect the contactor on the Battery Combiner to the positive connection point of the electrical system.
Use 4 AWG wire for the 200 amp model. Do not use shorter lengths of
wire; the tiny amount of resistance is helpful to reduce the maximum
current."


Just something for installers to know about.

EDIT: written before I saw Maine Sail's excellent solution.
 
Last edited:
Apr 5, 2009
1,433
Catalina '88 C30 tr/bs Oak Harbor, WA
On my system, I have an external regulated alternator with alt temp control. It is connected to a diode based battery combiner. The sense voltage is pulled from the AGM start battery and the voltage is regulated to what ever voltage I set. I set it to 13.6v to keep the LFP happy which undercharges the AGM by a bit but I can make up for that with a very small plugin charger set to the proper AGM voltages. The AGM and LFP are fully isolated except for getting the same charging voltage.

What am I missing?
 
Apr 22, 2011
685
Hunter 27 Pecan Grove, Oriental, NC
My original alternator charging setup was a dumb alternator output going to a 20 amp dc to dc charger inline with an agm start battery. The charger would send 20 amps to the lifepo4 batteries when the ignition key was on.

I now have a Balmar 100 amp alternator with external regulator. This allows quick charging of the lifepo4 batteries. Because I already had a dc to dc charger, I simply reversed the input and output cables and changed the charging profile to agm. So now the start battery receives the charge from the alternator/house bank whenever the ignition key is on. If I had not already had a dc to dc charger I would have opted for Main Sail's solenoid depicted above.
 

CarlN

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Jan 4, 2009
561
Ketch 55 Bristol, RI
MainSail - with the CMI Solenoid Load Dump you mention above - are you assuming that the charging profile for the drop-in lithium bank are "good enough" for the start battery? Or is there a 2nd charging system for the start battery that's not shown?