Kelpie
Well-known member
Well our first inverter died that way
An Affordable Lithium Boat Battery
- Thread starter migs
- Start date
B27
Well-known member
If you are reliant on your autopilot, radar, sounder.... your whole boat might get damaged.
B27
Well-known member
Surely one of the big advantages of Lithium is its ability to take bigger charging currents from the alternator at higher SoC?
Which a dc/dc charger is an expensive way of negating?
Also what happens when the starter battery dies of old age?
Kelpie
Well-known member
DC-DC is a relatively easy and safe way to integrate lithium. Upgrading the alternator is just a different approach which is generally going to be more work.
Not everybody needs to engine charge.
noelex
Well-known member
If the BMS disconnects the battery, any charge source that is connected to the house systems such as solar, wind, hydro, alternator etc can cause voltage spikes. The battery normally acts as a buffer keeping the voltage within acceptable limits, but if the BMS disconnects the battery this buffer is lost.
The voltage spikes may, and in many cases do cause damage to any of the house electronics such sailing instruments, chartplotter, inverters etc etc. This can be very expensive. It is possible to wire the house system in such a way that if the BMS disconnects the battery, the house systems will also disconnect, but you need to be aware of the issue.
A solution for the alternator also cannot just be ignored. DC to DC chargers are only suitable for low powered alternators. Our alternator is rated over 2kw, well beyond the capabilities of even multiple DC to DC chargers. There is little point switching to lithium, but having a much lower charger acceptance than would be easily achieved with lead. A high charge acceptance is one of the advantages of lithium.
These problems are solvable. I don’t mean to present a negative view of lithium batteries. They have many advantages, but there are issues to be considered.
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geem
Well-known member
Agreed. We have a single Victron 17A B2B (at 24v). More than enough for our needs. At night with everything running and motoring around the back of St Vincent a couple of nights ago, so autopilot, power hungry 14" chartplotter, a full suite of Raymarine electronics, 2 fridges, nwv light etc, we still had 7A at 24V, going into the battery. We don't need to charge from the engine.
An easy fix is to run multiple lithium batteries with their own BMS. The chances of all batteries doing a disconnect is vastly reduced. We monitor the lithium battery such that we are rarely at the full or empty part of the battery capacity. In fact, fully charging them doesn't really happen so an over current disconnect is an unlikely thing. In addition, we only run the inverter when we need it. It spends 95% of it's time switched off. We don't power 5hrough the inverter like lots of Victron installations
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Kelpie
Well-known member
I completely understand what you're saying but I should mention that in our case, I did just ignore it.
At least 80% of our electrical consumption is cooking. When the solar output is low, we switch back to gas, and even in the worst weather we have seen the large amount of PV we have has still kept up with all of the other loads. This has been mostly quite sunny places but I am surprised that it had worked so well.
I wasn't always planning on ignoring the alternator- in fact one of the first purchases I made was a 60A DC-DC charger specifically for this job. But I never got round to installing it because I just never needed to engine charge the batteries.
noelex
Well-known member
We also use engine charging via the alternator very little. We simply don’t put enough hours on the engine to produce significant amounts of energy.
However, it is our only source of power other than solar. We are almost never plugged into shore power (the last time was sixteen months ago) and have no generator or wind power etc.
With only two potential sources of power, redundancy is important and to reduce the maximum alternator charging to around the 0.3kw or 0.6kw typically available with a DC to DC charger does not make sense when over 2kw is easily available.
There have been times when high alternator power was useful even if its overall contribution has not been high. Winter in Scotland Is example where solar power becomes limited,
A DC to DC charger is not the only solution for a lithium installation and the full 2kw output can be achieved , but the simple answers that work well for lead cannot always be used with lithium.
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geem
Well-known member
This thread just goes to show the huge variation in the systems on boats and how diverse our needs are depending on how the boat is set up and used.
We have several different charging sources, generator, wind, water, solar and alternator.. We are one end of the spectrum. There are boats at the other end of the spectrum with no solar and just an alternator but with something like a Wakespeed regulator doing all the charging via a high output alternator.
No one solution will fit every application.
We have several different charging sources, generator, wind, water, solar and alternator.. We are one end of the spectrum. There are boats at the other end of the spectrum with no solar and just an alternator but with something like a Wakespeed regulator doing all the charging via a high output alternator.
No one solution will fit every application.
jakew009
Well-known member
2kW is about 150A at 12V or 75A at 24V. A couple of DC DC converters can easily handle that all day long: Battery Chargers Archives - Ablemail Electronics
Obviously if you’ve put a massive alternator on, then you are better off fitting a fancy regulator and charging the lithium bank directly.
However, for most people who are retrofitting lithium and don’t want to mess around with replacing the alternator, a DC DC converter is a very simple and safe way of doing it.
geem
Well-known member
One of the problems with DC DC chargers is they don't like heat. I just fitted the one charging my lithium bank from the engine battery when motoring with a computer fan to provide some cooling. It now works far better. I have a 24/12v charging the generator battery and another 24/24v doing the lead bank. These really don't see any load since they are only keeping those batteries on float. Something like 3 to 5w depending on battery size. They don't need any cooling.
A friend installed a Sterling DC DC charger and is disapointed with its output, I suspect for the same reason. Adding computer fans to them certainly helps. I am unsure why Victron or Sterling don't supply cooling or have it as an option for lithium charging
noelex
Well-known member
This is a possible solution, but I am not convinced it is the best solution for high powered alternators.
DC to DC chargers are a great option for low powered alternators when using lithium batteries, but I am not sure multiple DC to DC chargers are the best option for high powered alternators. Of course there is no perfect solution for ever application.
The maximum current of any of their units is 60A,and this is derated as the operating temperature rises. Multiple units would be needed for a high powered alternator. The efficiency is not quoted so it is not clear how much power would be lost. DC to DC chargers typically loose about 15% and some are significantly worse. The cost and installation complexity of multiple units would also be an issue.
Finally, and perhaps most critically, a DC to DC converter offers no protection for an overheating alternator. This protection can be critical for high power units if you want to extract the maximum performance. There are better solutions that will monitor the alternator temperature and gradually reduce the output as the alternator temperature rises. They will even cut all power if the temperature rises above a programmed critical value.
Yep, for the reasons mentioned above.
If you are staying with a low powered alternator a DC to DC charger is a good solution, but even lead equiped boats are fitting high powered alternators these days. It is a shame not to take advantage of the high charge acceptance of lithium.
Zing
Well-known member
I’m not so sure about that. LFPs are better in every sense, including cost (Self built and if installed from new), but as a retrofit the ancillaries costs may put people off. I use them as a starter battery in my motorcycles and outboard and they do extremely well. I find it extraordinary how the tiniest batteries deliver enough cranking amps and at faster speeds than lead.
vas
Well-known member
Reluctant to post to this thread as imho it seems to be going nowhere, v.quickly and it's only going to confuse newcomers (and possibly annoy others...)
After two years with my old trojan bank in parallel to the new lifepo4 304Ah 8S bank (24v boat) and a bluesea bi-stable disconnect (for the Lifepo4 bank if BMS is unhappy), I can confirm this is a cheap option to solve issues with power spikes messing alternator regulator, all nav instruments and all that jazz, with no need to buy B2B - obvs same can be done with a mosfet bms withouth the expensive disconnect h/w.
Just keep the old LA bank in parallel, job done (unless you're on a boat diet exercise which I understand is not a solution)
600W solar seems to be enough for my needs and running a 2kw watermaker every couple of days for an hour or so, plus all the other stuff I need in the med.
Fully agree with geem that there are many different scenarios for considering, adding (or even avoiding!) lifepo4, although OP useage pattern is not one I'd consider lifepo4 personally. Good luck to him trying to get a marketable project out of his work.
V.
After two years with my old trojan bank in parallel to the new lifepo4 304Ah 8S bank (24v boat) and a bluesea bi-stable disconnect (for the Lifepo4 bank if BMS is unhappy), I can confirm this is a cheap option to solve issues with power spikes messing alternator regulator, all nav instruments and all that jazz, with no need to buy B2B - obvs same can be done with a mosfet bms withouth the expensive disconnect h/w.
Just keep the old LA bank in parallel, job done (unless you're on a boat diet exercise which I understand is not a solution)
600W solar seems to be enough for my needs and running a 2kw watermaker every couple of days for an hour or so, plus all the other stuff I need in the med.
Fully agree with geem that there are many different scenarios for considering, adding (or even avoiding!) lifepo4, although OP useage pattern is not one I'd consider lifepo4 personally. Good luck to him trying to get a marketable project out of his work.
V.
PaulRainbow
Well-known member
I've been thinking along the same lines as you vas. Another option, rather than keeping a heavy/bulky lead acid bank, just fit a small lead acid in parallel.
The other point i agree with is, i cannot see why anyone with such a low power demand would consider Lithium.
vas
Well-known member
would do exactly that if the trojans are not helping sort out a slight list to stbrd in my case
and they were there anyway, so "free" !
geem
Well-known member
.............
The only problem is what happens when the lead battery goes bad? Say a cell goes down?
vas
Well-known member
Monitor temp and amps used - got the old bmv on the Trojans and use the bms current monitor for the lifepo4 bank.
migs
Active member
The link to the article in post #1 is now closed. My thanks to those who provided constructive comments.
PaulRainbow
Well-known member
Pretty much the same as when a single lead acid goes down in a bank of multiple batteries. Vas makes a valid suggestion, temp monitor/alarm.