In Part 1 we took a deep dive into alternator efficiency and concluded that we have to be careful to separate attainable alternator efficiency from marketing hype.
So are we all done? Nope, there are two other criteria to consider when selecting an alternator, and then two other system issues to take into account before pulling out the credit card.
And if we are considering an alternator with very high output instead of a stand-alone generator, we need to, once again, evaluate rationally and separate marketing claims from reality.
Alternator Selection Criteria
Let’s start with the two more selection criteria:
I count more than just two issues with 48v on a cruising boat: https://panbo.com/abyc-examines-the-48-volt-boat/
Hi Mark,
First I never wrote that the two I list were the only issues with 48 volts. To claim to have thought of everything is generally the mark of a fool.
Another problem that comes to mind is some switches and breakers tend to arc out at 48 volts. I bet there are more issues too, that I have not thought of.
And, yes, I read that one, but regarded it as a bit of a storm in a teacup, so did not bring it up. That said, I’m not a regulatory expert and if that worry does indeed come to pass it would indeed be a problem. And I have already warned many times about the importance of insulated tools because of high current, even on 12 volt systems.
Even if one does everything DIY and thereby avoids any issues arising from occupational safety regulations, the lack of common components rated to handle the nearly 60v present in a nominal 48v system presents significant challenges — and not just to boaters, but also to those installing nominal 48v terrestrial solar systems. For example, I am not aware of any 1-2-BOTH battery switches that are rated for more than a maximum (not nominal) voltage of 48v, and I only know of a single ON-OFF battery switch that is rated to 60v and has published certification to that effect. Even that one Victron switch isn’t ABYC C-7 compliant, so I literally know of no way to equip a boat with a 48v system that is fully compliant with the current ABYC standards.
Yes, safety regulations and industry standards can be ignored, and under-spec’d components used with the hope that they will prove adequate. What I am saying, though, is that 48v systems on boats still present many issues that 12v, 24v and even 36v systems do not.
A correction: With the recent update to E-13, a system like the Safety Relay functionality in some Mastervolt batteries should be ABYC-compliant without the need for a separate battery disconnect switch. Mastervolt’s Safety Relay system can be used with two of their 24v lithium batteries in series, so there is at least one way to build a fully compliant 48v system.
Hi Mrk,
I agree with much of that. But, we are way off topic here. I’m on record in many parts of this Online Book with the importance of properly rated switches, fuses, etc. The point is this chapter is only one in an entire body of work and if I duplicated every possible warning in every chapter they would all be 10,000 words and deeply boring.
As to not being able to build a 48Volt system to ABYC, I don’t know, but I doubt it. You might be right, but let’s not forget that the last time you said Victron kit did not comply (inverters) it turned out that was not the case. It would take a lot of deep searching to confirm that there is no 48 volt rated switch. Also, as I have said before, if I found a CE approved switch for 48 volts I would be good with that, and I bet most insurance companies would be too.
Anyway, I agree that 48 Volt systems are a PITA in many ways, and not worth it for most of us. Again, I’m on record on that in a bunch of places in this Online Book.
Using a Victron Lynx BMS still requires a battery disconnect switch as close to the battery as practical in order to be ABYC compliant. Let’s not forget that I was not wrong before the new E-13 came out, and I am still not wrong on this issue.
I would be much happier if you would post a link to a 60v-rated C-7 compliant 1-2-BOTH switch instead of writing that building the kind of 48v battery system that you advocate is not difficult or misrepresenting what I wrote. I still do not know of fully compliant battery switches. That is still not a claim that they absolutely do not exist.
And on the UL-compliance of Victron inverters, it was I who carefully followed-up and corrected my initial overstatement.
Hi Mark, Does you credit, but does not change that you were wrong and so maybe your general tone of certainty in your pronouncements needs a rethink, if for no other reason that it makes it easier to be wrong…I should know!
And if you want to get really picky about it, maybe that one available Victron switch is C-7 compliant in the sense that the same, unaltered switch may eventually pass C-7 testing, but it is not currently C-7 compliant because there is no published certification of its having passed the C-7 tests. Finding C-7 compliant switches can be tricky for even 12v and 24v. As far as I know, it is currently impossible for 48v.
Hi Mark,
I never said that building a compliant 48 Volt system was not difficult, rather the opposite. I just said that I thought it was probably possible. Nor did I misrepresent what you wrote. I just pointed out that it would take some deep searching to prove that no switches were available. Actually, in less that 5 minutes, I found several that said they were 48 volt and CE, but did not link because several of them were on Amazon and I always worry about fakes and did not have the time to dig deep. Anyway, this is totally off the topic of the post, so, once again, let’s end it here.
I would also ask that before you criticize what I write please ask yourself if said criticism has bearing on the fundamental point of my article. In my view many of your comments lately have not passed that test. You will find that if you apply it your comments will get a warmer reception like that received by those by Emile and Alwin, that enhanced the article rather than distracting from it.
[emphasis added]
“So my strong recommendation is that all 48-volt banks should be made up of at least two series strings, in parallel, of smaller-capacity batteries or cells, rather than a single string of high-capacity cells.
Not difficult to do, but worth thinking about before we buy a bunch of expensive batteries.”
It actually is difficult to do — or at least it is very difficult to source adequately spec’d 1-2-BOTH battery switches. Again, I’d be overjoyed to have some pointed out to me.
I didn’t start out by criticizing what you wrote. I simply and as succinctly as I could pointed out that there are more than the two issues that you mentioned in building a 48v system. In fact, the lack of availability of components like battery switches that the article I linked discusses bears directly on one of the two issues that you did mention.
You chose to expand the matter in a rather defensive manner instead of doing something more neutral like simply acknowledging that there are more issues and providing references to where you had previously discussed the issues raised in the panbo article.
In responding to you, I again avoided criticizing what you wrote and tried to stick to the facts that I thought were not being adequately addressed — viz. that building a 48v battery system as you described actually is a difficult thing to do.
In responding, you chose to go into what felt to be at least approaching ad hominem arguments.
I do not post carelessly or irresponsibly. If I make a mistake, I try to correct it as soon as I recognize my error. Yet no matter how I post, even if I very carefully couch what I am saying in terms of the limits of my awareness or knowledge, it certainly feels as though, if you are unaware or unfamiliar with the matter that I am posting about, that you all too often get defensive, assert doubt, disbelief or denial before even checking into the facts of what I am saying, and indulge in unfair attacks on my person that frequently repeat your fixation on my supposed “tone of certainty in [my] pronouncements” even when I have carefully avoided any such assertion of certainty. You did and have yet again misrepresented what I wrote.
If you make a mistake, if you misstate or overstate something, I wish you’d have the decency to admit it instead of diverting into defensiveness, irrelevancies or personal attacks. It gets tiresome. If you think the issue that I am addressing is not germane to your main points, then just point out where you’ve addressed my issue elsewhere; else clarify or correct the side issue as succinctly as possible without indulging in these unnecessary blow ups.
Hi Mark,
Time to stop. Let’s move on and both try hard not to irritate each other in the future. OK?
Hi Mark,
I got interested and did some research and I think you and Pambo are more right than I thought. There is a lot of information to parse here, but the key question is could 58 volts (max while charging a 48 Volt system) drive enough current through the human body to kill or maim? I used to think the answer was no and that the threshold was 60 volts DC but now I’m not so sure. I need to dig deeper to parse what is good science and what is regulatory alarmism, but I think we might be in a situation where all 48 volt systems should be fully insulated to the same anti-shock standards as AC 120 systems, or close. If so, that’s going to really cause problems for 48 volt boats since most (all?) of the gear tends to be poorly insulated against shock. I will try and break time loose to dig deeper and then update my article on choosing voltages earlier in this Book.
Anyway, thanks for bringing it up.
“ So my strong recommendation is that all 48-volt banks should be made up of at least two series strings of smaller-capacity batteries or cells, rather than a single string of high-capacity cells.” Should perhaps read “parallel”? Great article in any case! Love it when the takeaway for me is “don’t bother, go cruising”…
Hi Alwin,
Sure, that will clarify it even more, particularly for those who are not technical. I will add: “in parallel” after “two series strings”.
Glad the don’t bother worked for you. I personally would make the same call.
Hi, maybe slightly off topic, but would adding a higher voltage alternator and lithium bank (say 24 volt to stay within requirements), and then a DC/DC converter down to a 12 volt lead acid bank that feed the critical loads, be a reasonable way to fulfill the requirement to have a lead acid backup?
My boat is currently 12 volt, and I would say that 90% of the loads I have today is critical with the exception of the fridge. I would run an inverter and some other things from the 24 volt system. I’m probably missing something, but it does seem like a decent way of getting the benefits of both voltages, no need to change a lot of existing equipment, and getting a lead acid backup.
Also very timely articles as I am in the need for a new alternator (a couple days ago, a seawater hose came off and drowned my current alternator, which now gives me 5-10 amps… whoop whoop)
Hi Arne,
Sorry to hear about the alternator. Murphy’s law that the jet of water would hit the most vulnerable to salt water part of the engine!
Anyway, good question that I have been thinking about a bit. The good news is that of course if the 24 volt system craps out all the navigation and other critical loads will still stay up and running on 12 Volts. That said, the problem becomes if the 24 volt system can’t be fixed at sea and we have to go into get home mode on the 12 Volt since the 24 volt alternator won’t be able to charge it, and since we will suddenly be on a very small bank, alternator charging is vital. I guess the best option is a spare 12 volt alternator to swap for the 24 volt in this eventuality.
All that said, if my memory is good, you have a pretty simple boat without excessive power use so, at least if it were me, I would not take on the added complication of a two voltage system since I just can’t see a balancing list of benefits for doing so. So I would just replace the 12 Volt alternator with the largest under Eric’s guide lines and add a Wakespeed WS500 to get the most out of it, and make sure you don’t get stalling problems and that you have the top end available.
If 90% of your loads are “critical” then either your assessment of what “critical” means needs a re-think, or your boat’s systems are simple enough that you won’t really see a great cost to benefit ratio from 24V, lithium, etc. upgrades.
For all their flaws, simple lead-acid 12V systems have a really good cost to benefit ratio as long as they accomplish the tasks you need them to do. If the alternator in a 12V system blows, and the system generally met my needs otherwise, I’d normally just install the best 12V alternator I can get that’s well matched to whatever charging current my lead-acid batteries are able to accept.
I don’t recommend dual-voltage systems. They add complexity and cost, and they ruin your ability to MacGyver-up some kludge if things break 500 miles out from Tora-Bora. If I’m specifying a system as 24V then it is 24V throughout all main panels, all main batteries, & all main wiring; only a handful of low-power loads (e.g. electronics that are only available in 12V versions) get run via individual DC-DC converters or a DC-DC converter feeding a small 12V subsystem that is physically and logically local to that set of devices.
Hi, thanks to both! Yeah I don’t know exactly if 90% is correct, but the few things I have under passage that’s unnecessary (like the music player, some of the lights, phone charger…) they’re all easy to disconnect. Apart from the fridge (which I could easily turn off), I do think that 90% of the current leaving my batteries goes to essential things (nav systems, communication, autopilot…). I honestly can’t really think of what else could be running that would not be considered essential? But yes, I do think I have a fairly simple boost in that regard. At least not a lot of unnecessary power draw.
So yeah, I think the conclusion is that it’s not much benefit for me to switch to a dual voltage system. I do see some benefits with a lithium setup, but honestly, an appropriate alternator and regulator would solve most of the issues. I was thinking running a larger inverter-charger on a 24 volt system, but it’s not really something I NEED. More a thought as I’m already buying a new alternator and regulator.
Thanks a lot for both of your really helpful and direct replies!
Kindly, Arne
Hi John,
I agree with the conclusions here, of course. One slight problem, however, about the recommendation to split a lithium battery into two separate batteries run in parallel. That’s fully possible, of course, but it makes this double bank totally dependent on electronics that have proven their lack of reliability: Balancing circuits.
LFP cells treated right are inherently extremely stable. If the cells are properly matched, top balanced, and correctly connected (often not the case), they will usually stay perfectly balanced for years of heavy use. We need to monitor them and have a BMS to make sure that is indeed the case, but if all is right, they’re surprisingly smooth.
Pretty much all current LFP batteries have balancing circuits to make them work with poorly matched cells, that drift out of balance. This is not ideal, but works. When a battery of this type dies, it’s usually due to slow overcharge, but second is that a piece of the balancing circuits failed, killing a cell.
With two independent banks run in parallel, we need a way to keep the two banks balanced. That’s the same principle of circuitry, but running 14 times higher Voltage and a hell of a lot more power. It can be done, no problem, but is the end result more reliable? I don’t know. Myself, I’d prefer a single battery bank that was as simple as possible and that I understood and watched well. Much fewer points of failure.
I think the topic of this article will be far more relevant in the fairly near future. People want more and more stuff on their boats, and think their boat is a house. Electric propulsion is in its infancy, but it’s coming. This means higher voltages will be introduced. For relatively small sailboats we’ll be fine with 48V, but faster motorboats and bigger sailboats will need more. Probably the EV standards will move onto boats. That means many hundred Volts, locally.
Also the Sodium batteries mentioned another place, and some other chemistries, miss the decently flat Voltage curve of lead acid (11,8-14,4V) and the extremely flat curve of LFP (12,8-14V). Sodium for an imaginary nominal 12V package would seemingly go something like 8V to 16V. The benefit is that it’s easy to know the state of charge, SoC, but it will be impossible to use power directly from the battery bank. We’ll depend on converters or similar.
My guess is that within 5 years, we’ll see much higher voltage banks entering boats. They will operate more separate from the boat systems. More like a power plant onboard. Everything going into it or out of it will be transformed into what is needed for that purpose. The cells will be much cheaper than now, and last many times longer, like forever, but the systems as a whole will be more expensive, more complex and probably illegal for DIY. It will give new possibilities and much more efficiency. However, is it generally good for long distance cruisers? I strongly doubt it. I think it will be gradually harder to keep a boat simple, reliable and serviceable. Electric motors are so incredibly simple, reliable and cheap (really) that the industries are desperate to find other channels into our wallets.
Hi Stein,
As I understand it, Victron anyway, are perfectly happy to have parallel strings managed by the same BMS and will top balance them. That said, adding the 1-2-BOTH switch does add potential issues with lithium. I do cover those in other articles, but I think i will just remove that diagram from this article to keep things simple.
Hi John,
Yes, Victron are among the few who can do this in a probably quite good way. Partially because they use external BMSes and proper circuitry, like contactors rather than diodes. I have no doubt that it’s good.
For DIY LFP builds (not for the non nerds), it’s strongly recommended to put cells in parallel first, to get the required capacity, and then put those packs in series to get the required Voltage. The reason being partial self balancing, no electronics needed between cells in parallel.
However, my issue isn’t the details, which parts are used and how they are used, but rather the main principle. Two independent strings that are run in parallel needs something to keep them in balance, the exact same problem as between the cells in each separate string, but at a tens of times higher load.
The system needs an extra level of electronics. One more possibly weak link in the chain. Also, one of the basic KISS principles: “two objects fail twice as often as one object.” 🙂 We get two complicated battery banks in stead of one.
I don’t think it’s a bad solution to have two separate strings in parallel. I just think it’s worth considering how it actually improves total reliability. I’m not sure it does.
Hi Stein,
I don’t know for sure either. That said, let’s not confuse reliability and fault tolerance, two different things. A single series string has very poor fault tolerance, even if high reliability, since a single cell failing means there is no way to make whatever the target voltage is. To me that would be unacceptable on an offshore boat
I write more about how important this is here: https://www.morganscloud.com/2017/01/28/three-tips-to-make-your-cruising-boat-more-reliable/
On an offshore boat you could also have the best of both reliability and fault tolerance with Victron NG https://www.morganscloud.com/jhhtips/victron-ng-smart-lithium-batteries/
But even without NG, Victron seem perfectly happy with strings in series/ parallel and I see no reason why all cells should not top balance given that each battery includes it’s own balancing circuitry at the cell level. From the manual:
All documented in the Victron manual: https://www.victronenergy.com/upload/documents/Lithium_Battery_Smart/15958-Manual_Lithium_Smart_Battery-pdf-en.pdf