How are people charging Li/LA hybrid setups?

[donradcliffe]

I hook the alternator to the AGM battery, and use Smart Shore 200 lithium combiner between the AGM and the Life batteries. It is a voltage sensitive relay, and automatically combines when either battery gets to 13.8v, which is usually after the engine turns on. typically after the alternator turns on. Disconnect voltage is unspecified, but from experience the disconnect comes when the LiFe is nearly full. Solar is connected to the LiFe battery with bulk at 13.8 and float at 13.5. When I am not using the system, I force the VSR closed so that the solar also maintains the AGM. When I am motoring for extended periods, I force the VSR open after the LiFe battery is near fully charged. System and batteries are working well after 4 years.

[Ryban]

How is the VSR disconnecting your batteries Don? I was under the assumption that most VSRs are configured for LA systems, and will always bet in a "closed" state when one terminal is connected to a LFP bank, given the discharge voltage is much higher.

In any case, I've put some more thought into my plans, and am leaning towards a REC BMS for the LFP bank, which would enable the use of 2 contactors (one for charge, and one for loads), as well as CAN bus comms to my VenusOS running on a Pi. I suppose I could use VenusOS with this information to disable my victron compatible charge sources too.

I also drew in the battery switch/contactor (e.g. something like a 7713 or 7700 depending on how I configure it) that will connect the LA banks to the DC load bus in the event the BMS is about to take the LFP bank offline. That way important systems will (hopefully) continue running uninterupted.

Still not sure how I'll decide to handle the DC-DC chargers -- the Orion units can be configured to automatically detect when the engine is on, but if I want to use one in each direction, I would still need the 1/2 switch to prevent the output from one DC-DC charger from fooling the 2nd one into thinking the engine is on, and creating a circlular cycle. Alternatively, I can use a toggle switch wired to the Orion override switch terminals, such that one one unit is enabled, the other disabled, and forego the 1/2 switch -- but that's only modest cost savings.

[donradcliffe]

Originally Posted by Ryban

How is the VSR disconnecting your batteries Don? I was under the assumption that most VSRs are configured for LA systems, and will always bet in a "closed" state when one terminal is connected to a LFP bank, given the discharge voltage is much higher.

.

The "lithium" version of the VSR closes at 13.8 volts, while the LA combiner closes at 13.3 volts. Opening voltages are a bit lower.

[Ryban]

I've decided to split my house bank into two 4S batteries rather than a 2P4S battery, and also go with the more affordable FET base JK BMS. This changes the system layout a bit.

I think I can still get a signal out of the BMSes to engage a remote battery switch (e.g., to connect the LA bank to DC distribution if both LFP bats get taken offline), but I don't know if it can be done with a enough notice to avoid an uninterrupted connection.

The other problem with setup is that it would short the input/output of one of the DC-DC chargers (depending on switch positions). I don't actually know if this is a problem, but seems undesirable.

So I'm leaning towards a simplified setup without the remote battery switch. I can still switch which bank is powering DC distribution manually, and anyway, it seems unlikely that both LFP batts will get taken offline at the same time.

Images in order:
1. Remote battery switch allows for seemless transfer of power to LA bank if LFPs get disconnected
2. Same figure, but shorted in/outs to DC-DC chargers highlighted
3. Simplified, remote battery switch removed.

[Pete7]

Originally Posted by Ryban

I’ve been (over)thinking about this some more, and I’m considering swapping out the manual selection switch for which bank is providing power to the DC distribution bus with a remote battery switch. I could then use the BMS to trigger this switch in the event the LFP bank is about to be cut-off. I think this would be important in situations where the electric autopilot is doing its job, as interrupted power could be very unfortunate.

I think I could do this in a fairly straightforward way, but it’ll depend on which BMS I use and whether I want to do it through the VenusOS system.

"I’ve been (over)thinking" perfect example above.

How about one of these for a simple alternative system.

If you want to sail off grid, you have a choice of reliability and a "keep it simple" approach, or fixing complex systems in remote places when it all goes pear shaped. Which will you choose

[knutmi]

A battery monitor is essential for monitoring charging LFP (house)and AGM (start)togheter. I use Victron Argo Fet to separate both banks. Thats it.
I have VP engine with Mitsubishi 115 Amp alternator with max 14,4 V. When cold alternator I get about 110 amp, but when warm I get about 80 Amp. The voltage drops under charging empty batteries and increase when batteries are nearly full. When both battery banks share Amp from the alternator, I have never had any heat problem on alternator.
105Ah AGM
2P x 100 Ah LFP with 150A BMS
This setup have been running for 4 years now.

[dlj]

I like a self sustaining system that I don't have to think much about. I run all charging into my LiFePo house bank. I run twin alternators externally regulated with a Wake speed 500 controller. Both alternators have a sterling dump circuit in case the LFP batt's get full and cut off current in, but the Wakespeed does a good job without those, but they are there just in case. Solar, wind, Alts all charge the LPO house batteries. The shore power system runs through my charger/ inverter to also keep the house bank charged if I have to run a generator or plug into shore power.
Then I have two separate charging circuits running out one to my AGM start battery, one to my AGM thruster and windlass circuit. I monitor my house bank, it lets me know how everything is working.

No switches to remember, simple and robust. My AGMs are always fully charged so less problem of sulfation on those. All current into and out of the house bank is monitored so good house keeping on state of charge. Charging cycles are all optimized for the house bank. The AGM's get the correct charge cycle through the circuits coming off the house bank.

dj

[Ryban]

Originally Posted by Pete7

"[COLOR="Blue"]
How about one of these for a simple alternative system.

Haha I definitely laughed at that one.

I am by my nature someone that likes to automate things and make them as hands-off as possible with upfront effort. Sometimes this pans out, often it leads to complications down the road.

[pbiJim]

Originally Posted by Ryban

...

I updated my drawing to include the negative side to the bus and DC-to-DC chargers to also emphasize they're non-isolated.

Within the Victron world, there are 4 basic flavors of DC to DC converters. One is a battery charger that is isolated. One is a battery charger that is not isolated. The other two are straight converters that do not provide a charge profile. One of these is isolated. The other is not. They come in different sizes (different amp or watt capacities). The chargers tend to be more expensive.

[pbiJim]

Originally Posted by Bowdrie

Too many people mix apples and oranges and think they're getting pineapples.
Let the stock little internally regulated alternator do what it does best; charge the LA starting batts.
Mount a second big externally regulated alternator, (sometimes an off-engine mounting can work better,) and use it to charge the more exotic house batts.
Both batt systems get what they need without a lot of screwing around.

I like this idea for a couple of reasons, not the least of which is that after about 60 or 80 amps, a single V belt will not be able to pull the alternator hard enough without slipping & shredding itself. For higher amps, you will need a different pulley & a different belt.

I fabricated my first duel alternator set up more than 40 years ago. I like redundancy in a marine environment.

[pbiJim]

Originally Posted by Ryban

The long wire and battery switch isn't a bad idea. Or even an appropriately sized resister. I just fear that I'll forget and leave the switch closed after the engine is turned off.

I wonder if there's a relay/ACR that can be easily configured with a timer, where it will automatically disconnect after a set duration.

An industrial controls engineer can provide you with any configure of timing & regulation you might dream up.

[Pete7]

Originally Posted by pbiJim

An industrial controls engineer can provide you with any configure of timing & regulation you might dream up.

I have no doubt they can.

However, when Ryban is sat in

Fatu Hiva

wondering why the engine start battery is flat and why it won't charge, I suspect the solution will be to rip out all the complexity and go back to a jump lead or long wire and emergency battery switch.

Talking of which, why is a 230Ah battery (2 x 6v) required to start an engine on a 32ft yacht. Surely a group 27 will do nicely, with the jump leads ready just in case, but actually aren't going to be ever used. Just having bigger batteries doesn't reduce the risk of being flat and two 6v GC2 isn't the KISS solution, "one dead no startie".

Still not happy with the twin DC>DC chargers that switched by accident can create a loop sending a charge from one to the other and around again

[HeinSdL]

Side note, I charge the LFP via a 50A Victron XS DC-DC charger off my FLA engine starter battery. The alternator charges the engine battery as per original configuration.

Initially I wasn't very satisfied with the performance with excessive voltage drop between the engine battery and DCDC charger so I upgraded the existing cabling. Performance better but in fact the original Yanmar alternator wiring is far too lightweight too resulting in a massive 1.3V drop between alternator (producing 14.35V) and the engine battery (at 13V while the DCDC charger is operating at capacity).

So it would appear that the original alternator set up on the Yanmar (4JH3E with 50A alt) is designed for keeping the starter battery topped up and maybe a bit of additional charging of the house battery. But not along the lines of LFP requirements. So this needs to be looked into. Mine now has an 85A alternator but I still need to upgrade the relatively small amount of cables from alternator back to engine block/starter solenoid.

[Pete7]

Originally Posted by HeinSdL

So it would appear that the original alternator set up on the Yanmar (4JH3E with 50A alt) is designed for keeping the starter battery topped up and maybe a bit of additional charging of the house battery. But not along the lines of LFP requirements. So this needs to be looked into. Mine now has an 85A alternator but I still need to upgrade the relatively small amount of cables from alternator back to engine block/starter solenoid.

Had to do the same on our Volvo 2003. Whilst replacing the alternator, found the alternator negative wire was perhaps 6mm2 and ran to the engine block. Then another wire on the rear of the engine block to the batteries. This was original Volvo set up. Replaced with 25mm2 directly to the batteries and a second from the engine block to the batteries. Gained 10A straight away.

[HeinSdL]

Just one more thing to add to my earlier post: for Victron DCDC charger users the voltage drop you may live with but the engine off detection algorithm doesn't work very well, if at all.

The engine off algorithm requires a voltage setting below which the engine is considered off. So setting this voltage at eg 13V and then drawing 50A will mean the input voltage to the DCDC immediately drops below 13V (even with engine running, due to issue mentioned above) and so the DCDC throttles back to keep the input voltage at 13V. With excessive voltage loss on the supply side the charger might throttle back all the way to something like 10A which is nonsense. So one way around that is to set that engine off parameter to 12.3V and the charger goes back up to 40 to 50A (or override the engine off algorithm altogether). But then it will not stop charging once the engine stops... It will decrease the charging current to stay at 12.3, and drain the engine battery.