Tom and Bex

When our starter battery dies, I will likely do away with it completely and run purely from the lithiums. I've got an emergency switch to parallel them if needed, and the engine turns over and starts much quicker from the lithiums. Even s heavily discharged lithium bank will still easily start the engine. Ours are fused at 300A though which seems more than enough for our Isuzu engine! I think the arrangement I described in post 128 is about the easiest and least costly diy route, albeit with some compromises.

That's a myth. 1mph over the limit is still breaking the law. 10% + 2mph is national guidance that the police have, the end of the day it's up to individual forces to set there own limits on when they will prosecute or issue fixed penalty. I know several people who were given tickets a few years ago for doing 42-43mph in a 40 limit around Kettering.

Think that's the original code he sent me. I did modify it to use feature out as a battery combiner. Can't remember getting any errors, will get the laptop out tomorrow and have a play (need to modify end of charge anyway, would like tail current a bit higher to keep further away from knee on charge curve).

Worth trying, but wouldn't be so sure. My guess is it would spend a long time in bulk, and therefore a long time in absorption. Sounds like an interesting project. Could make a useful upgrade in the future, so if you don't mind sharing that would be great. Still way out of my depth, but a good learning experience for me! The problem with voltage based soc is how flat the discharge curve is. Be interesting to see how this works out. On our setup, we found the Victron BMV ah counter would drift if charge efficiency factor was set to 99% and give slightly high soc readings after several weeks, however with CEF set to 98% we have slightly low readings after a few weeks. That's one reason for us charging to 100% every 6 weeks or so - to re-synchronise the bmv. I'm glad we got ours when we did now! From memory it was only around $100 including shipping. Something like this could work quite well for lithium/lead hybrid installs. Set to isolate the lithium bank at 14v, and have it sensing from the lead acid. That way loads would still be provided by alternator whilst engine running, and the lithiums would take over when engine stopped as voltage would then drop below 14v. No discharge of the lead acid, and depending on alternator output vs lithium bank size, cuts charging around 80%. This setup, with a similar low voltage disconnect set to say 12.8, and cell monitoring with alarms such as ISDT BC-8S that we've used, could make for a fairly cheep but safe lithium install @Dr Bob. Worth trying, but wouldn't be so sure. My guess is it would spend a long time in bulk, and therefore a long time in absorption. Sounds like an interesting project. Could make a useful upgrade in the future, so if you don't mind sharing that would be great. Still way out of my depth, but a good learning experience for me! The problem with voltage based soc is how flat the discharge curve is. Be interesting to see how this works out. On our setup, we found the Victron BMV ah counter would drift if charge efficiency factor was set to 99% and give slightly high soc readings after several weeks, however with CEF set to 98% we have slightly low readings after a few weeks. That's one reason for us charging to 100% every 6 weeks or so - to re-synchronise the bmv. I'm glad we got ours when we did now! From memory it was only around $100 including shipping. Something like this could work quite well for lithium/lead hybrid installs. Set to isolate the lithium bank at 14v, and have it sensing from the lead acid. That way loads would still be provided by alternator whilst engine running, and the lithiums would take over when engine stopped as voltage would then drop below 14v. No discharge of the lead acid, and depending on alternator output vs lithium bank size, cuts charging around 80%. This setup, with a similar low voltage disconnect set to say 12.8, and cell monitoring with alarms such as ISDT BC-8S that we've used, could make for a fairly cheep but safe lithium install @Dr Bob.

We've got 320ah bulk charged by 2 x 70A A127 alternators, and absorption charged with 1 alternator. With our setup above 2 x 70A alternators, charging at around 100a, they consistently hit 80ish% when voltage hits 14.0v. A lot of these controllers use time in bulk to determine absorption time, ie if bulk takes a long time, then so will absorption. The complete opposite of what you want for charging lithiums! Same argument with lead acid! What is 100% anyway? We take 4% tail current at 14v as 100% soc, but tempted to increase that to 5%. Current does drop much much quicker than lead acid, but still takes us over an hour to get from 80% to 100%. Again, just to reiterate though, you don't ever need to get to 100% with these batteries!

14v will easily reach 100% soc and easily overcharge if left at that. 13.8v will probably also reach 100% as well, just take a bit longer. Yes, charge current is important to consider in all this as well. We generally see around 100A or a bit less during bulk charge (depending on engine revs). Batteries tend to spend a lot of the bulk charge at 13.65-13.7v, and are about 80% charged when they hit 14v. We noticed current would tail off too gradually for us if charged at 13.8v. That is on a 320ah bank. Remember these batteries were designed to be charged at 1c until pretty much full, but that requires a much higher finishing charge voltage than ever likely to be used in a typical narrow boat installation. One point to consider if powering the BMV from the lithium bank is it will always be drawing power from that bank, even if low voltage disconnect operates. Not a significant problem if prompt recharge occurs, but could be potential issue for leisure boaters leaving boat unattended for some time. As to leaving 6 SLA batteries in place, don't really see what it would achieve? You would have the constant power wastage of trickle charging 6 batteries from the lithiums, instead of just 1. Lead acid should remain full at all times, our (pack level) low voltage alarm is set at 12.8v and never sees that in normal usage. Sounds very interesting. Any plans to sell it? Need any testers?

As are we. Never go back now though. Could even be tempted to dispense with our starter battery if/when it fails. Yes to the cost. Our install cost a little over £1000 - £600 was batteries, and the rest extras. Not sure where the 50-60% comes from though, we've charged ours to 100% and discharged down to 9% with no issues.

Except I only rarely charge to 100%. Usually operate in the 30-80% range. As Nick says, you can get to 80% quicker by charging to 14.0v and then stopping charge. We'll just have to see how long these cells last, I guess. I think it's still a learning curve for the manufactures as well if you look at how their recommendations on voltages have changed over the years, but remember, our market sector is insignificant to them, so no research into our usage rarely takes place. I'm quite good at destroying things even without a dremmel! As to deciding when to stop charging, our setup will charge to 100% if left to it's own devices, and then switch to "float", except it monitors current, and tried to keep it as close to 0A as possible (but due to failsafe max voltage, in reality discharges to low 90's% before stabilising which suits us fine). Again, all fully customisable. We also have a switch to force "float" mode at any time, often used to stop charging at 80-90% when on extended cruising. "Float" mode is also activated automatically if temp drops to freezing at the batteries. I think Nick's answered most of your other questions already. If you PM me your email I'll send the files on to you as well (and anyone else who's interested). To be honest, this is all a bit (lot!) out of my comfort zone! Just glad to have something that works well, and is programmable to my exact needs.

As voltage rises (very slowly!) during bulk charge, then when it hits 14.0v that equates to approx 80% soc. Continuing charging at 14.0v (absorption) until current drops to say 4% gets you to 100%. If you continue to charge at 14.0v (or any voltage that allows current to continue to flow into batteries) you will overcharge them, regardless of what that voltage is. Yes should do, will try to get them over to you later. I liked this when looking at BMS options, but cost put me off in the end. Can only speak from my experience of A127 alternator, but found it relatively easy to disable internal reg and connect wire for external reg. Although brush holder is built into reg, I believe to disable with a switch, there is a wire running to spade terminal on reg which you could cut into, maybe @Sir Nibble could confirm? Is it that big a problem running from the batteries when fully charged? Doesn't do them any good to sit at 100% for too long, and shouldn't affect overall life much if they dropped to say 80% by end of day, then a bit more overnight. With lithiums you really do need to completely rethink your ideas on battery usage and charging, and forget about everything you learnt re lead acid batteries! That's exactly what our arduino controller can do if set up for lead acid instead of lithium. Has an input to enable equalization mode if set up for it. Connects to an existing shunt to measure current flow into batteries. A quick note re lithium charging voltages, we started with charging at 13.8v, but found we weren't able to make best use of lithiums ability to accept quick charge, so settled for 14.0v as a good compromise. That's still only 3.5v per cell if well balanced, which is well within the safe charging voltages. Just a personal decision though, we were slightly disappointed at first charging at 13.8v.

I have a copy that he emailed me if you want it?

It's good that more people are looking at lithiums now, they've certainly simplified our charging regime over winter, and dramatically reduced engine running time to an average of about an hour a day. I think the benefits to heavy power users or those living of grid should be clear now. To pick up on a few points raised above, the handling of alternator charging is definitely one of the more tricky areas to handle. I'm really glad we went for the controller we did, and we did manage to get a 3rd generation one ready made up and just mounted it in a cheap box. A shame if it's now going to be commercialised, but I guess that was inevitable at some point - no doubt at very significant cost increase! I'm not sure of any currently available commercial alternator controllers that have the same features, particularly the monitoring of current. I guess that will change in the future as best practices with lithium batteries filter down, the trouble is we are such a tiny fraction of the market, it's not worth it for most companies. Balmar have a controller that is claimed suitable for lithiums, and I believe Mastervolt do as well? Not really looked into them much though after I chose the arduino route. As to disconnect devices, I went down the separate charge and load bus route, so needed 2 heavy duty disconnects. I considered using relays or contactors, but decided even with energy saving circuits, I did not want to put up with the continuous drain having the coils energised. I opted for the BEP 701-md motorised battery switch for the load side, which was quite easy to install and wire to BMS, and probably one of the simpler options. For the charge disconnect, I used the TE BDS-A 190A latching relay. This relay is used on some Ford's as a battery disconnect (possibly transits?) so can be obtained 2nd hand. The big problem using latching relays is the control of them, they require a brief pulse to switch on or off, but most control systems, BMS etc just have a steady output, either on or off so you need to use an interface circuit with them. An alternative way to terminate charge, could be to use alarm outputs on a battery monitor such as Victron BMV 701. This could be set at whatever end point you choose, based on current, voltage, or SOC. Personally, having had these batteries now for 4 months, I would set it to re-synchronise to 100% at 14.0v, tail current 6%, and take this as 100% charged and turn off charge sources at this point. Another alternative charge control method could be use of an adjustable voltage sensing relay or board, and set this to cut charging when voltage reaches say 14.0v. This is what we do with our alternator controller to get additional bulk charge from engine alternator - standard split charge relay that opens when 14.0v is reached. We find this consistently occurs around 80ish%, and is usually when we stop charging. Every 4-6 weeks (or when out cruising) we do a full charge to synchronise BMV to 100%, but notice very little drift. Trouble with this is the exact point could vary depending on current (e.g. due to engine speed) and you sacrifice some useable capacity. Having said that, ours usually operate in the 30-80% range. Hope this answers some of your questions @Dr Bob and good luck with your installation.

I know the advice here it's to always do a power audit, but how many people on here have actually done a power audit? And how many did one before getting a boat (and if so how accurate was it!)? I know we use about 100-120ah per day on average, but that can vary quite a lot depending if we are home or at work, using washing machine etc. Some days are as low as 60ah or less, and others as high as 160ah or more. I only know that from monitoring actual usage, not from any power audit.

Some VDO tacos have to be calibrated with a cable and dedicated software. Possibly plugs into socket marked 123?

Not that uncommon. When looking to buy our current boat, all Black Prince boats we looked at had it wired this way, as did some other hire boats. 2 batteries dedicated to domestic use, 1 dedicated to Eberspacher, and 1 engine start battery.

As Nick says, ideally the system should be designed so the cell under and over voltage protection never activates and is there as a fail safe only. If the under or over voltage cuts in there had already been a failure of some sort, so the protection cuts in to save the expensive batteries from destruction. It would be cheaper, but would rely entirely on manual intervention to protect potentially very expensive batteries. Depends how much risk you are prepared to take. Having said that, these batteries are more robust than many think though. That's why we use the ISDT BC-8S to monitor cell voltages and have set the alarms to alert me prior to the BMS high and low voltage levels. This has quite a loud alarm (90db?) considering the size and price, certainly loud enough to hear above the engine whilst cruising, and at the opposite end of the boat. Initial (top) balancing should be done by connecting all cells in parallel, and charging at 3.8v until current drops to pre determined level. You can do manual rebalancing whilst cells are connected, by noting which cell(s) are slightly high/low at end of charge, and applying a load across high cells to bring them more in line (or charge low cells). This can involve a bit of guesswork though, and parallel balancing is the preferred method. Having said that, experience shows rebalancing should rarely be necessary. Unfortunately, unless you use the valence ones such as peterboat where you can connect up computer to see number of cycles and other usage data, you have to rely on the trustworthiness of the seller. About the only other checks that are easy to do, are check for any bulging of cells, and check voltage level.

Can't remember seeing that one before. I was looking at the smart 123 BMS from here https://www.ev-power.eu/Battery-Management/123-Smart-BMS-Complete-Set-4-cells-with-Bluetooth-4-0.html but went with a simpler and cheaper option in the end.

I got mine from here http://arduinoalternatorregulator.blogspot.com/?m=0 and think it cost about $120. Came fully assembled, but as just a board so mounted it in a cheap box from Toolstation. Found the chap extremely helpful when emailing him with questions, I had zero experience of arduino and programming prior to this, but with his help was able to set it up and change some of the parameters to suit my needs. Says currently out of stock but always worth an email. He wasn't pushing me for a sale at any point, just very helpful with my enquiries. Not sure if it's the same seller, but I did look at these when I was looking, but unfortunately they had sold out.

This is what I've done to ours. I seem to recall you can only remove it from inside initially, I accessed it from the top with the flue removed before installing. 2nd squirrel I've done this on, now fixed with 2 bolts from outside into metal bar that holds it on. Quick and easy to clean behind boiler now! The other way I've done it is vacuum cleaner hose down flue from on top. Often alternate between this and removing rear blanking plate. Surprising how much you get out!

I think this thread demonstrates the range of options available from the very basic with owner doing the monitoring and taking any action necessary, to the complex fully integrated (expensive!) systems from the likes of Victron and Mastervolt etc. I suspect most real life systems fall somewhere between these 2 extremes (as does ours). Our 2nd hand cells came from http://www.ev-support.co.uk and we paid £600 for 8 Thundersky 160ah cells. Those ones MTB linked to above look like good value if they are as they say they are. If anyone interested is in the Lapworth area, I'd be happy to show them our system and talk it through with them.

That was the main motivation. No running the engine/generator for 8hrs putting in single figure amps into the batteries! Yes - although alternator controller needs to be fully programmable and to replace existing regulator functions. Ours has connections to the BMV shunt so can be programmed to change charge settings based on amps flowing into battery instead of pure voltage. Low voltage cut is strongly advised - can be based on pack voltage, but to gain max usable capacity a cell voltage cut is recommended. High voltage can be taken care of with alarm, generally you would be present during charging (solar excepted but with conservative values should be fine). That's why I went for (2nd hand) bare cells. My total setup cost just over £1k including additional wiring improvements. I did consider paralleling the lithiums with the lead acid initially, but the cost savings weren't that great in the end. As to charging with generator, we can only charge at 30A with genny compared to over 100A via alternators so negating one of the big advantage of lithiums to accept high charge rates. I did look at his system, but it was way to expensive for me to consider so I designed my own to be as simple but safe as possible within a tight budget. This was after many hours reading articles and discussions online and coming to my own conclusions as to risk vs benefit of the different options. I was pushed into action by the need to replace our 12 month old cheapo batteries that were down to considerably less than half original capacity! That's why after careful consideration I decided to locate ours inside just next to the rear steps. Our alternator controller takes care of not charging them below freezing, but can't imagine many scenarios where they will get that cold inside the cabin. Hopefully if it's that cold and we're away the solar output will be quite low. Solved with a low voltage cut, particularly if based on cell voltages. Need to be careful nothing bypasses it though - this includes battery monitoring! It's not quite as simple as that, it comes down to how you determine 100% again! As there is no need to ever charge to 100% then why bother? Our setup is arranged to take 100% as being tail current of 4% @ 14.0v but think that's pushing it a bit really and thinking of changing it to 8%. If you look at the charge curves you can see how little capacity you put in at the end of charge as the current tails off and voltage rises rapidly. Some people charge to a set voltage such as 14.0v and then stop. My experience seems to show that takes you up to 80-85% which might be enough and certainly gives a big safety margin. It's important to remember not to let any individual cell go higher than 3.6-3.7v during normal charging, and avoid holding them at that level. Whilst on the subject of charging, it's worth mentioning temperature compensation. This should be disabled on all charging sources. It's not needed and risks cells going over voltage in cold weather - almost the opposite of what you want. Unless you have alternator connected to start battery and combine them for charging. Alternative is to cut charging by cutting the power to external regulator if used or ?field wire if internal reg, but this requires modification of alternator. One of our alternators is modified to use external reg and the other charges the start battery and is combined with the lithiums until they hit the absorption voltage of 14.0v. That's what I hope our system is designed to do. Having lived with it for a couple months or so now, I'd be fairly confident to do away with some of my safeguards and rely on low voltage cut off based on pack voltage only, and alarms for the rest. If you don't mind losing a bit of useable capacity, then just have a high voltage cut set to 14.0v, charge to there and stop. That avoids the need for alternator and other charge controllers. Having said that, I'm very happy with our setup, the performance of it, and the peace of mind it gives.

I think lithiums are becoming a more proven technology than lead carbon, particularly for off grid use. One of the biggest hurdles to overcome I think is how to successfully/safely manage alternator charging. I've used a separate arduino based alternator regulator, but it does require modification to existing regulator. I'd be interested to hear how other lithium users have managed this.

But your batteries never get to 100% in winter............ Get yourself some lithiums - you know you want to?

I got the feeling most people switch everything off when leaving the boat - we tend to just leave it all switched on, as we would in a house.....

I do have a simple BMS that provides high and low voltage cut based on individual cell voltages. Bought from Australia as was the easiest and simplest I could find for the price. I'm sure a basic alarm such the ISDT device above would be fine for users such as yourself who know their usage pattern and are prepared to monitor the batteries themselves. My primary concern was what would happen if we were away for several days with the fridge on. That's my primary reason for the BMS I chose.

Bare cells. 2nd hand 160ah Thundersky cells to be exact. Only Victron item I've purchased is the BMV monitor. Generally charged from alternator controlled with arduino alternator controller. Charged at 14.0V until amps drop to 12A (4% battery capacity). This is taken as my 100% charge. 100% charge is ok, it's over voltage and holding at high charge that kills cells. That can happen quickly at the end of charge. Float mode on the alternator aims to keep amps flow into battery at 0A (with a max voltage of 13 point something). This generally lets them discharge to mid 90's% before amps stabilise at 0.