Having completed electronics and electrical refits on multiple yachts over the years, I've gained valuable experience, having had the chance to experiment with, and evaluate, a number of different products, vendors & technologies.
|Bonne Amie's original DC panel from 1955|
The most important lesson I have learned is that it's really easy to make things too complicated.
- Keep the systems as simple as possible
- Lithium House Batteries
- Lightweight, Odyssey cranking battery
- Just one single AC Outlet in Navigation
- Provision for SFC Fuel Cells (Supplemental Green Charging) for long passages
- LED Light Conversions Throughout
- Engine Driven & Solid Fuel Heat Only
- NKE Wind Instruments & Pilot
- Cobham (Thrane & Thrane) SAILOR VHF Radios
Roll Your Own or a Purpose Engineered, Marine Specific Li Battery System?
I have dealt with Bruce Schwab at Ocean Planet Energy on two projects, and I cannot speak highly enough of Bruce or Ocean Planet Energy. I can't imagine anyone else in this market has Bruce's expertise in this specific area. If you're considering an Li installation on your boat, or green power on your yacht, you need to call Bruce. Because of this relationship, and my past successes working with Bruce, I would never consider rolling my own Li batteries.
It's just not worth the effort or risk when I can buy a complete system designed by someone who has forgotten more about Li batteries than I'll ever learn for just marginally more than rolling my own.
While there are folks out there who are fully capable of building their own Li house battery system (and it is a complete system, not just a battery), I am not. So I'm going with a proven expert in the field, and a tier-one battery manufacturer who has worked with Bruce to design Li batteries specifically for the offshore sailing market.
Why Lithium Batteries?
I've put Lithium batteries on two boats now, and as far as I'm concerned, there is simply no better choice for house banks now that Li technology has matured. Lithonics, Mastervolt, Genasun and others all make incredibly reliable batteries, all safer than lead in many respects.
Here are some key things I consided with when deciding between AGM & Li:
- Total Cycle life of AGM batteries is compromised if 'Depth of Discharge' (DoD) exceeds 50%
- The top 20% of capacity in AGM is very slow to accept charge
- Poor Charge Acceptance rate, a typical G31 AGM's is optimally charged at ~30A, with a max rate of ~40A, compare that to 1C (or better) rates on Li
- In fast charge scenarios, only 30% of an AGM's capacity will be usable
- High loads (rapid discharge) of AGM batteries significantly reduces their capacity
- Despite the reduced 'Charge Acceptance Rate' (CAR) of AGM above 80% charge, full charging is necessary to prevent sulfation
- ~15% of amps in are lost due to inherent charging inefficiency with AGM batteries
- Limited Lifespan (400-500 Charge Cycles)
- The real world usable capacity of Li batteries is 80-85% of total rated capacity
- Li is light weight: ~25% for same usable capacity with AGM
- Li's charge acceptance rate can be up to 3x total capacity, typically 90-95% for maximum cycle life
- Li requires no temperature regulation of charge voltage
- Li has an extremely high cycle life with 3000-5000 cycles being very common
- Li has greater efficiency for big loads (windlass, etc). Same number of Ah in as out
- Li has dramatically less voltage sag in discharge cycle, with virtually no Peukert’s losses
Some very relevant musings on the Lithium subject, including information on making home baked Li banks, are available on Compass Marine's website. It's a fantastic article, and there's a lot in there everyone.
A Real World Use Case
Let's look at a real world use case. We're going to take a long day sail to a remote anchorage from our mooring in the islands. We'll do the trip in two identical boats, one equipped with AGM, the other with Li. Both batteries have an equivalent total rated capacity of 120Ah.
Starting with fully charged batteries, we apply a constant load of 9A (instruments, autopilot, minimal systems, refrigeration, perhaps some music on the stereo) for the duration of our sail.
The 140A alternator has sufficient reserve output during charging to absorb this fixed 9A load while the engine is running.
In keeping with the manufacturer's recommendations, we will only discharge the AGM to 50% before we begin recharging the battery, the Li battery will be discharged to 20%, according to the manufacturer's guidelines, before recharging.
We will start our experiment at 7am, as we sail off our mooring.
Sailing with AGM
We depart from our tranquil mooring on the AGM equipped yacht at the prescribed 7am. Under the 9A load we are able to sail until 1:40pm before we must start recharging the batteries.
Because the acceptance rate is only optimal until we reach 80% total charge on the AGM, we will charge only until this point to save fuel.
While we have a 140A alternator, the maximum charge amperage of the AGM is only 40A, but RECOMMENDED charge amperage is only 30A to maximize cycle life! So we cap the charge program at 30A.
Factoring the AGM's 15% charge inefficiency, we calculate that we can only effectively deliver 25.5Ah to the cells per hour.
It will take 2 hours and 21 minutes to charge the battery back to 80% of it's rated capacity.
At 4:01 we are finally able to turn off the engine and continue our sail in peace.
We've brought the battery up to 96Ah of it's rated 120Ah capacity, leaving only 36Ah before the engine needs to be restarted, again.
By 8:01pm, after only four hours, we have once again exhausted the AGM battery. We need to charge for another 2 hours and 21 minutes to bring us up to the limit of the battery's optimal absorption. At 10:22pm, as we approach our anchorage, we once again have a full charge, having consumed a total of 96Ah of battery, and replaced a total of 96Ah.
We've run the engine for a total of 4 hours and 42 minutes.
Sailing with Lithium
On the Li equipped boat we slip our mooring at 7am as well. We're applying the same 9A load, but this time we won't hit the battery's reserve capacity until 5:40PM after 10 hours and 40 minutes of sailing. This is a big improvement over the AGM's performance as we've been able to sail an additional 4 hours before starting the engine to top up the batteries.
We have consumed 96Ah of the battery's capacity and have 16% of safe reserve before critical voltage drop, but we decide to turn on the engine and begin charging the bank.
With it's high acceptance rate and charge efficiency we are able to deliver 100A (0.9C) of charge to the battery, and will stop charging at 95% of it's total capacity or 114Ah of the total rated capacity of 120Ah. We need to put 94A back into the bank at this point, but at 100A of charge we accomplish this in just 57 minutes.
It's now 6:37PM and we have 94Ah to burn until the next charge. By 10:16PM when we arrive at anchor, we have only consumed 33Ah of the 94Ah we have remaining. Turning on the engine for the final 16 minutes prior to dropping the anchor handily tops up the Lithium battery while we furl sails, do a bit of pre-anchor maneuvering, and drop the hook. It is important to note, however, we would typically leave the battery partially discharged, as Lithium has no issue sitting partially discharged, unlike AGM which prefers being fully charged.
We've run the engine on the Li powered boat for just 73 minutes compared to 4 hours and 42 minutes on the AGM boat. That's 73 vs 282 minutes on the engine, or a savings of 209 minutes of engine run time in just a single day's sailing. That's HUGE!
Computing the Real Cost Per Usable Ah
For rapid charging scenarios, what most sailors face offshore (given the tiny size of most of our fuel tanks), we need to compute the cost of batteries not by some factory rated capacity, but by usable capacity in the real world (we don't live in some battery engineer's lab).
That's 82.5Ah of real world usable capacity in a rapid charge environment. This battery is not effected by partial charging or storage at partial charge levels, unlike AGM's, meaning significantly less headache.
Putting it All Together
So with all this in mind, the decision to go with the Lithonics with an integrated NeverDie BMS seemed a no-brainer for the house battery. The 12V110A-30H-CTRL200 was chosen as it can be easily doubled for offshore racing at some future date, and the internal BMS eliminates complication of the overall system.
Shore Power will connect only to the Sterling Power 12v-30a Pro Charge Ultra charger, which will be used to charge the Li bank when dockside power is available. These beautiful chargers are compact (10.25x8.5"), fully programmable, and the 30A unit is less than $550.00.
While these are 110v, they do operate at 50Hz. Considering all the equipment we might use on the boat has auto detecting power supplies (laptops, small appliances, etc), this is of no real concern.
The alternator, rectifier and regulator will be supplied by Mark Grasser at DC Power Solutions in Eliot, Maine. Mark is THE expert in the field when it comes to alternators, rectifiers and regulators.
Not only are Mark's products the best you can buy, they are typically priced lower than the inferior competitors, so there's absolutely no reason not to go with the best.
In order to maintain charging efficiency we need to reduce heat, and with any high output alternator, most of the heat is produced by the diodes in the rectifier. By putting these in a purpose built case with their own heat sink, heat soaking of the alternator is almost entirely eliminated. The result is an alternator you can still touch with your bare hand after running at full output for nearly an hour. Try that will your Balmar alternator.
Marks custom regulators also have a very nice field cut feature which can be wired directly to the electrical panel or a switch at the helm. With this enabled the field strength is cut to float, giving you all that horsepower back to propulsion in heavy seas or in an emergency. The best part, it's cheaper than even the most reasonable competitor, and the quality is top notch.
All of this will me monitored by a Phillippi System Monitor from Ocean Planet Energy. This will be discretely mounted in the navigation station inside the sliding cabinet, out of view. I will be able to extend this to tank monitoring at some point should we chose to put tank monitoring in.
These can be integrated with any brand of product, and can monitor all shipboard charge sources and loads.