Re-designing battery storage system

[jimp1234]

I've owned my Westsail 42 for several months, and I'm now getting around to re-designing the battery storage system on the boat. I currently have a single Grp 8D AGM battery rated at 185 Ah acting as the house bank, and 2 Grp 24 engine starter batteries all located in the engine room. I also have a Newmar Phase 3 charger, an Onan 6.5 kW genset, and a standard 70A alternator on the engine. My electrical audit calculation shows a draw of 320 Ah per day during passage, with the two biggest draws being the hydraulic auto-pilot and refrigeration. My plan is go with 600 Ah of LFP batteries (w/ external BMS) installed in a new battery box outside the engine room. This should give me at 75% DOD, 450 Ah available. I'm hoping that with a high-out alternator (probably 180A) along with the genset that I can recharge the LFP house batteries using either the engine or the genset in less than 3 hours run time per day.

So here's some questions. I'm not quite sure how best to compute charge times though it's obviously dependent on the output capacity of the charger I select. Any examples or ballpark numbers based on your setup for recharge times? What chargers should I consider? Also what's the best option for charging the AGM starter batteries? DC-DC charger? I like the idea of solar, but I don't have a big davits, or an arch, so unless I'm missing something do I need to consider it as an additional charging source with this setup? Finally, my genset sits right above my engine, making it very difficult to work on the engine and the genset. Can I eventually get rid of the genset? This is my first draft of the plan so please let me know what I'm missing and what other things I should be thinking about? TIA


-Jim

[GordMay]

Originally Posted by jimp1234

... I'm not quite sure how best to compute charge times though it's obviously dependent on the output capacity of the charger I select..

It's probably more dependent upon the acceptance rate of the batteries.

[john61ct]

Lead takes 7+hrs no matter how many amps available

[Sailmonkey]

Originally Posted by john61ct

Lead takes 7+hrs no matter how many amps available

The op was talking about LFP batteries of 600ah.

To the OP, how many amps is your charger?

[tkeithlu]

The 70 amp alternator could be maxed out if you are charging the house battery as well as the starter batteries from it. If an alternator has to run 100% of the time charging, it will overheat. Consider a larger one. I also suspect that you will want more house capacity. Very rough rule of thumb, and battery pros on the forum can tell you more, but I figure on twice the amp rating from the alternator to the amps I want during that long seven hours of charging that John mentions.

[john61ct]

> Grp 8D AGM

If you stay with lead, it is very rare to find true deep cycling batteries in 12V and especially automotive sizes.

If you do go to LFP for House. That will accept (pull) a too-high rate of charge unless your gear limits charge current. Especially important if the alternator is used for House, need to fit DCDC chargers, or upgrade to an external VR like Balmar MC-614.

> 3 hours run time per day

Good, for a 600Ah bank that's a maximum rate of 200A. Trying to go faster will not be great for longevity, 150A actual current flow is a better target.

[john61ct]

Originally Posted by jimp1234

I'm not quite sure how best to compute charge times

For a 600Ah bank, 1C current is 600A, 0.2-3C best range for LFP, is 120-180A, (Ah per hour) or 3-4 hours if well depleted.

What chargers should I consider?
Really want user-custom setpoint adjustability.

Victron or Magnum for combi inverter/charger type.

Sterling Power ProCharge Ultra or ProMariner Pronautic P series for standalone charger.

> Also what's the best option for charging the AGM starter batteries?

If your LFP setpoint will be unacceptable for your Starters, yes a DC-DC charger is one solution. But just converting to a compatible chemistry when they need to be replaced (even if a bit sooner) would be simpler, KISS.

Allows you to use a standard ACR/VSR, amps required is low so even an Echo Charger is enough.


> I like the idea of solar, but I don't have a big davits, or an arch, so unless I'm missing something do I need to consider it as an additional charging source with this setup?

Not with LFP, but at least some solar is pretty much required for House bank longevity if it is lead, unless you're using ICE sources 7+ hours a day for other purposes anyway.

> Finally, my genset sits right above my engine, making it very difficult to work on the engine and the genset. Can I eventually get rid of the genset?

Of course your alternator setup and engine usage patterns (plus solar, hydro etc) must be providing for your daily energy needs first.

Redundancy is good, so maybe carry a little portable Honda inverter genny as backup?

[Rorzech]

Dacian Todea at Kickstarter sells a little 100 amp charger the size of a pack of cigaretts that hooks directly to your solar panels and to each of your LFP cells shows voltage in each cell also. He told me people usually use a Vicron which can be remote operated by the BMS. I ordered two of them because i live off grid and on the boat when the time comes. I'm still working on figuring out this whole big world of Lifepo4 batteries. so far I found out you can't wade into it, you need to get ready to jump in with both feet first and hang on for the ride. So far i think Lifepo4 got Lead Acid beat by a country mile. I couldn't imagine anyone in their right mind ever going back to Lead Acid. Who want's to keep breathing all that lead toxicity belching out of those ridiculously heavy salt water unfriendly lead batteries ?

[CatNewBee]

Look at the spec's of your batteries first.

If built from Winston cells, you can charge with 1C, turbo-charge with 3C (not good for a long life), I would recommend 0.5C or 300A.

You need an inverter anyway I guess. Why not buying a Victron Multiplus or Quattro, they have a built in charger. The Quattro 12/5000 220 100-100 is a 12V unit, providing 5000VA 220V output, has a 200A charger inside and 2 power transfer switches rated 100A each for the 220V inputs. You can team them up for higher currents, combine them for two or three phase systems, they have a power assist function and can be programmed to anything you need, including grid feedback.

With the 200A charger you can charge 400Ah in 2 hours by your genset easily.

https://www.victronenergy.com/invert...argers/quattro

[alamoana]

I would try really hard at getting rid of the genset. Good alternators plus solar is a good option. Gensets are great if you need them for AC or water maker, but I understand you do not need it and it is a lot of weight, maintenance and limits access to main engine. I would review the 320 AH consumption, it seems too high to me; maybe you can measure it like with a BMV 702 or similar? LIFEPO4 can be charged at almost any rate yet alternators above 100 Amps become large and wiring heavy, so I suggest calculating for 100 A, maybe 150 A alternator. I want to believe your consumption is aprox 200 AH per day, alternator to provide 100 AH and solar the next 100 AH. Assuming 5 PSH you need to produce 20 A per hour which is possible with 300 watts of panels. Good luck

[a64pilot]

I’d say that even with a 200 amp small frame alt that 100 amps continuous charge is pushing one decently hard, above 100 may be in the damage area from heat.
100 amps is a good number.
Assuming you keep the generator, I would it’s there and paid for, then I’d go as big as feasible charger wise, often really big chargers are in big inverters, as a combo.
Solar is great, really great for lead, and of course works for Lithium, but if I had a generator and was going with Lithium, I’m not so sure I’d mess with Solar.
It’s not an insignificant amount of money and windage, and to many just plain ugly.

[zemurray]

320 AH a day sounds like a lot for just basic usage. Maybe if your running a TV, microwave, toaster, etc? Wow..

My autopilot isn’t hydraulic, but I run a new Engle fridge, charge a phone and iPad, and LED lights and it’s somewhere between 40-75 a day. Depends on if we sail through the night. My fridge is using around 25-30.

[newhaul]

Originally Posted by jimp1234

I've owned my Westsail 42 for several months, and I'm now getting around to re-designing the battery storage system on the boat. I currently have a single Grp 8D AGM battery rated at 185 Ah acting as the house bank, and 2 Grp 24 engine starter batteries all located in the engine room. I also have a Newmar Phase 3 charger, an Onan 6.5 kW genset, and a standard 70A alternator on the engine. My electrical audit calculation shows a draw of 320 Ah per day during passage, with the two biggest draws being the hydraulic auto-pilot and refrigeration. My plan is go with 600 Ah of LFP batteries (w/ external BMS) installed in a new battery box outside the engine room. This should give me at 75% DOD, 450 Ah available. I'm hoping that with a high-out alternator (probably 180A) along with the genset that I can recharge the LFP house batteries using either the engine or the genset in less than 3 hours run time per day.

So here's some questions. I'm not quite sure how best to compute charge times though it's obviously dependent on the output capacity of the charger I select. Any examples or ballpark numbers based on your setup for recharge times? What chargers should I consider? Also what's the best option for charging the AGM starter batteries? DC-DC charger? I like the idea of solar, but I don't have a big davits, or an arch, so unless I'm missing something do I need to consider it as an additional charging source with this setup? Finally, my genset sits right above my engine, making it very difficult to work on the engine and the genset. Can I eventually get rid of the genset? This is my first draft of the plan so please let me know what I'm missing and what other things I should be thinking about? TIA


-Jim

on the Spencer 42 we only used an average of 120ah underway and about 90ah at anchor .
Even running a technautics refrigeration system . I would think that you would be at a max 200ah per day.
A 200 amp alternator with external regulator and 300 to 400 ah lifepo4 . You already have the genset do get a good 2000/100 inverter charger ( 2k inverter with 100 amp charger ) .
Throw in 400 or so watts solar and your good to go .