Induction Hob (and air fryer)

[Neeves]

Cheaper BMSs, including those found within the budget 'drop in' batteries, do not have separate charge and load buses. So if you relied on the BMS to regulate charging, you'd find the battery going offline and you'd have no power.

By the way, there is a type of BMS, the Electrodacus, which is designed to also function as a charge controller. Only works with 12v (nominal) panels, and it's strictly a DIY job. I investigated it and despite its many advantages chickened out, it seemed a very complicated solution.

I wish I had not asked . .......!

If the BMS of the drop in batteries does not regulate charging ..... what does it do?

Budget lithium batteries are sold with a BMS - what does it manage ... if not charging (and cell equalisation) and I recall Geem suggesting they mostly were poor at managing cell equalisation (which is why he does not like the internal BMS).

Jonathan

 

[Pete7]

I wish I had not asked . .......!

If the BMS of the drop in batteries does not regulate charging ..... what does it do?

Budget lithium batteries are sold with a BMS - what does it manage ... if not charging (and cell equalisation) and I recall Geem suggesting they mostly were poor at managing cell equalisation (which is why he does not like the internal BMS).

Jonathan

Most drop in BMS's act as an on/off switch. When the battery or cell voltage hits a predetermined value charging or discharging, the BMS disconnects the battery. Hence the black out Kelpie referred to. They will also cut out if the voltage fall too low or you try and charge the battery below a set level. Charging at 0'c or below will permanently damage the battery. Mine are set to 5'c, which is the lowest water temperature likely to be seen in the Solent.

There is a solution to a complete LFP disconnect, most likely to happen when the LFP is fully charged and that is to put a lead acid battery in parallel. Sadly the US advisory group ABYC have "outlawed" the idea. They haven't provided any research to support their action. The good news is they are only advisory even in the US. For those of us in Blighty we can ignore them, in fact the hydrid LFP and LA is quite popular on the canal circuit. We have a hybrid house bank. For those down under, you may have problems with your insurance brokers also being a short sighted when it comes to LFP.

Andy one of your fellow countrymen has done a huge amount of research into LFP and cell balancing. This is worth watching and explains what happens to LFP particularly when you get into the "knee" at the very end of the charging cycle.

 

[Kelpie]

I wish I had not asked . .......!

If the BMS of the drop in batteries does not regulate charging ..... what does it do?

Budget lithium batteries are sold with a BMS - what does it manage ... if not charging (and cell equalisation) and I recall Geem suggesting they mostly were poor at managing cell equalisation (which is why he does not like the internal BMS).

Jonathan

The BMS does nothing, until one of the parameters you set is reached. Then it disconnects the battery.*
It's simply too blunt a tool to use for things like charge regulation.

* I sightly over simplified. One of the parameters is to turn on cell balancing, but that has no external effect. But basically everything else the BMS does involves disconnecting it from the system, or reconnecting again once back within safe limits.

 

[noelex]

But some might charge their Lithium direct from solars and then the solar regulator seems unnecessary.

Using the BMS to regulate charge sources such as solar is considered an acceptable practice on a camper trailer. So you can use this system and save some money in your application.

Most readers of the forum will be considering a marine installation and this practice is not acceptable on a yacht at least on lithium batteries with an internal BMS.

The difference is that important safety systems on a camper trailer, such as the electric brakes, rear lights etc are controlled by the lead acid battery system on the tow vehicle. The lithium house system of a camper trailer can be disconnected without any safety implications.

This is not true on a yacht. Here the house system powers systems such as navigation lights, VHF, depth sounder and navigation instruments etc. The loss of these systems at an inopportune moment can effect the safety of the vessel. While nothing is foolproof, the electrical system on a yacht needs to be more robust. If your have drop-in lithium batteries with an internal BMS, using this BMS for charge control is not acceptable.

Drop in lithium batteries with an internal BMS cannot seperate the charge and load bus. Therefore, to regulate the charge voltage the BMS will shut down the whole battery, preventing discharge as well as charging. In applications such as a camper trailer, the solar panels can just be unplugged when this occurs and operation restored, but the temporary loss of power may create significant problems on a yacht.

An MPPT solar regulator also performs voltage conversion and thereby extracts more energy from the solar panels, something an internal BMS cannot do.

 

[noelex]

If the BMS of the drop in batteries does not regulate charging ..... what does it do?

The protection systems that may be incorporated into the BMS of your drop-in battery include: high and low voltage, high and low temperature and high current. Not all BMS units have all these features, with low temperature protection frequently omitted in the cheaper ones.

These protection systems are best thought of like a fuse: a safety system that should not be activated unless there is a problem. The difference is that a fuse protects the wiring and a BMS protects the battery, but they are both systems designed to prevent damage in circumstances that should not normally occur.

The BMS also has a seperate function to balance the cells. This function is necessary to keep the lithium battery healthy and prevent problems over the long term. Some BMS units will also comunicate parameters to the owner such as individual cell voltages, battery temperature and SOC.

More sophisticated BMS systems can comunicate with charge sources such as the alternator to shut down charging before the battery disconnects in a fault condition. This is helpful to prevent damage, but this level of communication and control is not normally incorporated into the simple and reasonably priced drop-in batteries.

 

[Alan S]

There is another approach to solar charging of lithium.

In my setup it's a DIY 48V LiFePO4 battery used for propulsion and cooking (but I think the same idea could be used for a 12V domestic system) charged direct from solar with no solar controller. The Vmp of the panels is matched to the charging Voltage of the battery.

Instead of a BMS I have a CMU (cell monitoring unit) from Elerix which pulses a latching relay to sound an alarm and cut off the solar if any cell reaches 3.5V although I usually switch off manually before this. It also sounds an alarm at 3.0V on discharge (this has never happened except once to test it) but does not cut off load. I don't see the need for this as I am always on board when discharging.

As far as I can see most BMSs are designed only to protect the battery from extreme overcharge and discharge, they don't care about your electrical system.

 

[noelex]

There is another approach to solar charging of lithium.

In my setup it's a DIY 48V LiFePO4 battery used for propulsion and cooking (but I think the same idea could be used for a 12V domestic system) charged direct from solar with no solar controller. The Vmp of the panels is matched to the charging Voltage of the battery.

I love simple systems. The KISS philosophy is often the best approach on a yacht .

Keep in mind that there are some compromises in your system. One of the biggest is the Vmp of the panels will vary significantly depending on conditions so it is impossible to match the Vmp with the battery voltage without some electronics. I would consider the added complication of solar controllers worthwhile.

As far as I can see most BMSs are designed only to protect the battery from extreme overcharge and discharge, they don't care about your electrical system.

Basically, this is correct. In many cases the action of the BMS in protecting the battery can potentially hurt the yacht‘s electrical system by, for example, damaging the alternator diodes. Most consider the BMS a necessary evil to prevent the risk of catastrophic damage to the expensive lithium batteries. Your manual system can do the same, but it requires active human intervention.

 

[Alan S]

The points you make, Noelex are perfectly valid for most but...

The Vmp does not change much with light levels but does decrease with high temperature but this would only reduce output if the battery voltage was at the higher end of it's range so not needing a lot of charge.

Anyway the panels are over specced for summer to still provide useful output in summer.

I'm not convinced an MPPT controller would in the real world provide significantly more Ah per day on average than a carefully matched Vmp panel directly feeding LiFePO4.

As you say, Keep It Simple Sir.

 

[noelex]

Ideally the Vmp of the solar panels is perfectly matched to the required charging voltage. This is only possible with an MPPT controller electronically adjusting the input voltage.

Without this electronic mechanism solar panels need to be selected so that the Vmp is always above the charging voltage. This is because if the Vmp of solar panels is below the required charging voltage the solar panel output is drastically reduced. If the Vmp is above the required charging voltage the penalty is much smaller.

Without the voltage conversion technology of an MPPT controller the aim is to ensure that in any reasonable conditions the Vmp is always above the charging voltage.

So in practice, before MPPT controllers were available solar panels had a much higher Vmp than typical charging voltages. This is why so called "12v” panels have a Vmp around 18.5v, way above any potential charging voltage.

Without MPPT technology it is claimed by the manufacturers that the average solar panel output is reduced by around 30%. I think this is an exaggeration. The real benefit of tracking the Vmp correctly with an MPPT controller is more like 10-15%, but nevertheless this is a nice gain for little extra complexity. The technology also applies automatic voltage protection preventing damage to the lithium batteries.

Notice how this graph below of typical solar cell shows how the power drastically falls off if the voltage is even slightly higher than the Vmp.

 

[Neeves]

I deduce the background and recommendation is to build your own battery. Much, or all, of the correspondents here seem to have done this.

But is this the same in the rest of the world, outside this forum. Do boat builders who install Lithium actually build their own batteries - or do they simply go off and buy off the shelf 'drop in' batteries with internal BMS. Do chandlers sell drop in batteries. If I ask someone like Paul Rainbow to instal a Lithium system (and my suspicion would be most people would not build their own battery) what does the local yacht sparky instal.

One of the cautionary comments made by Forum members here is that building you own battery should not be conducted by the neophyte. If this is the case the neophyte either finds someone to build a battery for them - or they buy a drop in. The drop in is quick and easy - its just needs a credit card - so the majority of owners (I might guess - and as I have said - never guess), will have drop ins.

If I build my own battery - I wonder what the views are of the insurance company, as insurance was raised in an earlier post - and do insurers prefer build your own or drop ins?

I'm not arguing against building your own - just wondering what happens outside of this forum (and the various YouTube proponents). I'm not arguing against use of a solar controller - just asking, what seem to me, to be obvious thoughts of a neophyte.

Interestingly there is some dissent amongst the experts here.

Jonathan

 

[Kelpie]

Maybe 'assemble' is a better word than 'build'. The latter conjures up an image of somebody recreating a factory in their shed, when it's more like plugging stuff together.
I knew almost nothing about electronics before going down the DIY route. I can use a multimeter and a spanner, which are the only tools required. You also need to buy an adjustable power supply that works in the 3-4v range.
It's really not rocket science to assemble four cells and a BMS.

Buying drop-ins isn't really saving all that much work. You still need to design the rest of the system, which is where a lot of money and knowledge come in. In most cases there's going to be a lot of new wiring, fuses, changes to other components, etc. None of this stuff goes away just because you bought a 'drop in'. Which is why it's not a very good term.

 

[noelex]

Building your own lithium battery bank saves money and generally results in significantly better performance compared to what is available from drop-in replacements of equivalent cost.

However, drop-in replacement lithium batteries are coming down in price and improving in performance, so this distinction may be temporary. Time will tell.

Commercial boatbuilders cannot endorse home made lithium batteries, or even many of the drop-in solutions from non marine companies. Often the only solutions from boatbuilders are the two systems from Mastervolt or Victron. Both excellent systems, but expensive for what they offer. Rival marine sytems are being developed and this competition can only help us consumers.

 

[Alan S]

Noelex,
Quote
"Notice how this graph below of typical solar cell shows how the power drastically falls off if the voltage is even slightly higher than the Vmp."

I have studied these curves for my panels and the Vmp changes very little between 100% insolation and 10%.
It does reduce at high temperature but that is not a problem in winter when you need all the charge you can get. In summer there is usually a surplus anyway. So a nominal Vmp 2 or 3V above typical charging Voltage 52-54V works fine for me.

I dont think the cost and complexity of an MPPT controller would be justified.
A few more Watts of solar would be a better investment.

Having said this, every situation is different and this might not suit everyone, especially Mr Victron et al ; )

 

[Kelpie]

I dont think the cost and complexity of an MPPT controller would be justified.
A few more Watts of solar would be a better investment.

Having said this, every situation is different and this might not suit everyone, especially Mr Victron et al ; )

I've noticed with land-based projects a tendency to 'just add solar'.
That doesn't work so well on a boat, where the main constriction might be space, not budget. For most people an MPPT is a worthwhile investment, because we're already carrying the maximum amount of solar possible.

 

[Alan S]

I've noticed with land-based projects a tendency to 'just add solar'.
That doesn't work so well on a boat, where the main constriction might be space, not budget. For most people an MPPT is a worthwhile investment, because we're already carrying the maximum amount of solar possible.

Not land based. 300Ah 48V LiFePO4, 1180W solar, 6Kw outboard motor and 1500W inverter for cooking on a Hardy 25 mostly on inland waterways. I could squeeze in another 100W of panels or so but don't feel the need for that or an MPPT. The system has worked well for 2 years.

 

[noelex]

The voltage vs production curve is not symmetrical . If the Vmp of the panel of the panel is 54v and the required charging voltage is 52v there is very little loss of efficiency. However, the reverse is not true. If the panel Vmp is below the required charging voltage, the production is severely affected (see graph).

For this reason the voltage input must always be equal or above the Vmp. However, without the voltage conversion inherent in MPPT controllers this excess voltage is wasted.

The bottom line is that MPPT technology significantly increases the energy extraction available from solar panels.

You can install a simpler system with no solar controller, but the solar yield will be lower.

 

[Alan S]

I wonder if anyone has done a proper scientific test of MPPT versus carefully matched panels with no controller on LFP batteries?
I would be amazed if the MPPT produced more than 10% advantage over a typical summer or winter's day.

 

[Alan S]

The voltage vs production curve is not symmetrical . If the Vmp of the panel of the panel is 54v and the required charging voltage is 52v there is very little loss of efficiency. However, the reverse is not true. If the panel Vmp is below the required charging voltage, the production is severely affected (see graph).

For this reason the voltage input must always be equal or above the Vmp. However, without the voltage conversion inherent in MPPT controllers this excess voltage is wasted.

The bottom line is that MPPT technology significantly increases the energy extraction available from solar panels.

You can install a simpler system with no solar controller, but the solar yield will be lower.

Worst case scenario for efficiency would be something like battery charging voltage 50V, cool sunny day panels directly facing sun Vmp might be 60V (I don't have exact figures to hand) so "wasting" 10 V. More typically batteries charging at 53V, warm day, sun at shallow angle to panels, Vmp might be 55V so close to ideal match but leaves a little headroom for less favourable conditions.
under the worst case scenario above I would get something like 20A instead of 25A with an MPPT. Not really a problem on a sunny day.

 

[Kelpie]

I wonder if anyone has done a proper scientific test of MPPT versus carefully matched panels with no controller on LFP batteries?
I would be amazed if the MPPT produced more than 10% advantage over a typical summer or winter's day.

One thing that would put me off is that the majority of readily available and good value panels are around 32v nominal, which is not a useful voltage to have on a boat. So you'll be converting it to either 12, 24, or occasionally 48v anyway.

As I mentioned upthread the Electrodacus can be used with simple relays to function as both a BMS and a charge controller, for 12v systems. One of the reasons I didn't choose it was because I didn't want to be stuck with 12v panels, which tend to be smaller and poorer value than the ones produced for rooftops.

 

[GunfleetSand]

The Lidl air fryer is in store today, no mention of an induction hob