Battery tech

[odysseus2000]

What confuses me are the statement that lithium ion batteries can not provide enough starting amps. At my local garage I watched a mechanic start a diesel with a flat battery using what appeared to be a small lithium ion battery pack. There are several similar sized devices on eBay, all saying they can produce around 400 amps to start a car & are lithium ion battery packs.

Are these devices not as described or is there some other “magic” that allows these starting feats to happen? Or are marine diesel in need of many more than 400 amps to start?

Regards,

Lithium can produce very high current but the typical, off the shelf leisure batteries have BMSs to limit the maximum discharge current. Normally the maximum discharge rate corresponds to the battery capacity in Ah, so a 100Ah battery would be limited to 100A. Any more than that and the BMS disconnects until the load is removed. Those little LiFePO4 jump starters are specifically designed to deliver much higher currents, but for short periods.

Thank you!

So in principle with appropriate wiring & two batteries with appropriate BMS one could replace both the starter battery & the bulk storage battery with LiFePo. To have just one battery like as in a car would need a BMS with no or a very high current limit for discharge & a charging management that would both ensure correct charging & heating during cold weather. The latter probably troubles the concept as several days in the cold would exhaust the battery due to its heating mandate else one would have to schedule a pre-heat before starting. The use of a mains heater as is common in Canada for oil sumps would also make this feasible, but few in the uk would like the inconvenience.

The blessing of having a BEV is that with the large battery & an HVAC (heating, ventilation & air conditioning) one can more quickly warm the battery pack & one also isn’t troubled by needing high cranking amps to start.

Regards,

[odysseus2000]

Interesting how one can now get free electricity for two hours a day at peak times & store that energy with an Ecoflow power station:

https://blog.ecoflow.com/uk/octopus-ene ... gJJ8PD_BwE

A 2.2 kWh Ecoflow power station is around £1700 on eBay from a quick peruse, which with normal power at circa 30p per kWh, requires 1700/0.3 = 5667 hours to break even. Assuming 2 hours per day, that is 15.51 years & all that power used. (Note the marketing is confusing, often they quote the max supported power for short use & then the true storage power, easy to get confused!)

It seems likely that the eco power stations will fall in price with battery storage now around $139/kWh:

https://www.latitudemedia.com/news/stor ... s%20cobalt.

So for a 2 kWh system the batteries cost $278, then there is an inverter at say £120 & a max power point BMS (something simpler if only charging off the grid) going for similar, the likely material & componentcost is around $278 + £240 =£219+240 = £459, suggesting the Ecoflow could fall by around £1200 & still give manufacturers margin, in a business to consumer sale, but more if also needing to give a retailer margin.

Not sure shares in electrical generators with fossil or nuclear generation are good investments given these economics as these kinds of numbers will likely bring on more renewables as the cost of fueling, & uncertainties in supply, of traditional power stations is not as attractive as it was just a few years ago. Sure we still need them, but we need them less than we did & likely even less going forwards & that must impact their economics.

Regards,

[clissold345]

I have read about the long cable trick to limit the charge current, but what I was confused about is what stops battery overcharging. Or do you really [rely] on the BMS for this?

I have the BMS set to turn charge off at 14V and turn it back on at 13.5V. Why do you call the long cable a "trick"? Does electrical theory predict it will work? Does it work? Is it reliable? Is it safe? Is it cheap?

[hiriskpaul]

I have read about the long cable trick to limit the charge current, but what I was confused about is what stops battery overcharging. Or do you really [rely] on the BMS for this?

I have the BMS set to turn charge off at 14V and turn it back on at 13.5V. Why do you call the long cable a "trick"? Does electrical theory predict it will work? Does it work? Is it reliable? Is it safe? Is it cheap?

Yes it works, but is a bit of a bodge. Let’s say you want to limit the charge current to 40A, the alternator outputs 14.5V and your minimum battery charge is 12V. That means you want to drop 2.5V along the cable. Ohm’s law V=IR gives a cable resistance of 2.5/40 = 0.0625 Ω. Oceanflex 6.0mm² 50A cable has 0.00323 Ω/m, so you need 0.0625/0.00323 = 19.3m.

As a safety check, if you have 50A going through the cable, the voltage drop would be 50*0.0625 = 3.125V. Alternator 14.5V – 3.125V = 11.375V at the battery, so should be safe unless the battery is really depleted. Note though that the charge current will decrease as the battery charges up, eg at 13.5V, dropping 1V along the cable, the current will only be 1/0.0625 = 16A. A proper battery to battery charger will keep charging at its maximum output until nearly full.

As to price, 19m of Oceanflex 6.0mm² 50A cable (9.5m each black/red) is going to cost around £50. So yes, cheap compared to a Victron Orion 30A battery to battery charger, which is about £200. The Victron is going to be safer though and would charge more efficiently.

If you limit the BMS to 14V, then the batteries are not going to be fully charged. That is not necessarily bad is it will prolong their life. You should use a proper LiFePO4 charger occasionally though as the BMS will likely not perform cell rebalancing at 14V.

[clissold345]

Yes it works, but is a bit of a bodge. Let’s say you want to limit the charge current to 40A, the alternator outputs 14.5V and your minimum battery charge is 12V. That means you want to drop 2.5V along the cable. Ohm’s law V=IR gives a cable resistance of 2.5/40 = 0.0625 Ω. Oceanflex 6.0mm² 50A cable has 0.00323 Ω/m, so you need 0.0625/0.00323 = 19.3m.
...

You're keen to dismiss use of a long cable in this situation. First it's a "trick" and now it's a "bodge". I'm not sure you're right. Eg I think there are other resistances in the circuit that mean a very very very long cable is not required. If you want details of long cables and "hybrid" setups, look at the facebook group I mentioned. Why is the Victron box safer? If you want to use a Victron box, do so!

[hiriskpaul]

Yes it works, but is a bit of a bodge. Let’s say you want to limit the charge current to 40A, the alternator outputs 14.5V and your minimum battery charge is 12V. That means you want to drop 2.5V along the cable. Ohm’s law V=IR gives a cable resistance of 2.5/40 = 0.0625 Ω. Oceanflex 6.0mm² 50A cable has 0.00323 Ω/m, so you need 0.0625/0.00323 = 19.3m.
...

You're keen to dismiss use of a long cable in this situation. First it's a "trick" and now it's a "bodge". I'm not sure you're right. Eg I think there are other resistances in the circuit that mean a very very very long cable is not required. If you want details of long cables and "hybrid" setups, look at the facebook group I mentioned. Why is the Victron box safer? If you want to use a Victron box, do so!

I have just been granted access to the group, so I will take a look.

Please don't feel offended by my use of words such as bodge and trick. This long wire "technique" will work and has the advantage of simplicity. Essentially you need to limit the load on the alternator. One way to do that is to that is to increase the resistance in the circuit. LiFePO4 batteries have miniscule internal resistance, so the resistance is in the cables and connections. The other way is to introduce a battery to battery charger. This will provide more precise control over the charge current, but has the disadvantages of cost and complexity.

I think there may be a difference in safety emphasis between yachties and other users such as RVs and probably barges. If you are out at sea or in remote places you really do want to minimise the risks of blowing your alternator or damaging your batteries. The yachty forums tend to be disdainful of the long cable technique and most seem to use B2B chargers. In addition, the advice of the RYA and yacht engineers is never to mix LiFePO4 and lead in the same bank. There is a dislike of relying on a BMS to disconnect for example and to treat this as a last resort safety device. It could fail and lead to overcharging and a fire. A B2B charger will disconnect when the battery is 100% charged. If it fails, hopefully it fails "closed circuit" and if not, the BMS is there as a secondary safety device. Another difference is that on a yacht you tend to use the engine infrequently, so really want optimum charging when the engine is on. Having said all that, I am not averse to looking at the long cable technique and mixed chemistry setup again as I think some of the concerns and objections may be overblown for my use and I do appreciate the simplicity.

ps, my alternator is only 55A. I could replace it but it is a rock solid piece of kit. Putting a bigger alternator in woud decrease reliability.

[clissold345]

I have just been granted access to the group, so I will take a look.

Please don't feel offended by my use of words such as bodge and trick. This long wire "technique" will work and has the advantage of simplicity. Essentially you need to limit the load on the alternator. One way to do that is to that is to increase the resistance in the circuit. LiFePO4 batteries have miniscule internal resistance, so the resistance is in the cables and connections. The other way is to introduce a battery to battery charger. This will provide more precise control over the charge current, but has the disadvantages of cost and complexity.

...

ps, my alternator is only 55A. I could replace it but it is a rock solid piece of kit. Putting a bigger alternator in woud decrease reliability.

Keep an open mind! Battery chemistries can be mixed under certain circumstances. Safety is important to you. What's the best way of improving safety? Fast charging is important to you. So yes if a B2B provides faster charging, it makes sense for you to have one. I hope you find the facebook group useful!

[DrFfybes]

Interesting how one can now get free electricity for two hours a day at peak times & store that energy with an Ecoflow power station:

A 2.2 kWh Ecoflow power station is around £1700 on eBay from a quick peruse, which with normal power at circa 30p per kWh, requires 1700/0.3 = 5667 hours to break even. Assuming 2 hours per day, that is 15.51 years & all that power used. (Note the marketing is confusing, often they quote the max supported power for short use & then the true storage power, easy to get confused!)

A lot of confusing bumf about.
https://givenergy.co.uk/ claim you can save 85% of your home energycosts if you have the tenacity to persevere on their diabolical website to actually find some information.

13.5kWh capacity, 6kW max power from their all-in-one unit (includes inverter, BMS, off grid capability) is about £7k installed, which bang for buck is better than the Ecoflow. For most houses that would allow cheap charging and cover all your use, but the 85% claim is probably based on some model scenario using the Octopus smart tariff where they control your battery.

Paul

[hiriskpaul]

I have just been granted access to the group, so I will take a look.

Please don't feel offended by my use of words such as bodge and trick. This long wire "technique" will work and has the advantage of simplicity. Essentially you need to limit the load on the alternator. One way to do that is to that is to increase the resistance in the circuit. LiFePO4 batteries have miniscule internal resistance, so the resistance is in the cables and connections. The other way is to introduce a battery to battery charger. This will provide more precise control over the charge current, but has the disadvantages of cost and complexity.

...

ps, my alternator is only 55A. I could replace it but it is a rock solid piece of kit. Putting a bigger alternator in woud decrease reliability.

Keep an open mind! Battery chemistries can be mixed under certain circumstances. Safety is important to you. What's the best way of improving safety? Fast charging is important to you. So yes if a B2B provides faster charging, it makes sense for you to have one. I hope you find the facebook group useful!

Safest way would be not to charge off the alternator at all! Which might work if I had sufficient capacity. I need to try and size it better, but I reckon on about 50Ah per day, maybe a little less when at anchor or somewhere with no shore power, so 350Ah should last a week. Probably enough and could extend with a small amount of solar.

Alternator charging is very inefficient, but in emergencies I could connect up with a long cable, but switched off most of the time

[9873210]

The blessing of having a BEV is that with the large battery & an HVAC (heating, ventilation & air conditioning) one can more quickly warm the battery pack & one also isn’t troubled by needing high cranking amps to start.

Regards,

A BEV is designed as an integrated system with significant engineering effort. They are building thousands or millions of identical units. Secondary characteristics of components matter. Even when all the headline specs match second sourced components are rarely "drop in". There are a lot of edge cases built into the software. A home brew system will have hours rather than years of design effort and has to compensate with huge margins to avoid rather than manage edge cases.

[GrahamPlatt]

A different take on the storage heater

https://www.euronews.com/green/2024/03/ ... year-round

[odysseus2000]

A different take on the storage heater

https://www.euronews.com/green/2024/03/ ... year-round

The idea has been around for a long time, but nice to see a more practical sized system.

The primary trouble with sand batteries is that the energy is low grade, suitable for heating, but not much else.

Stored electricity by contrast can be used for almost anything including heating.

Nevertheless there are folk in the uk arguing that for many properties a sand battery heat storage system is better than a heat pump in terms of its ability to heat a poorly insulated house in very cold temperatures where a heat pump struggles. In heat storage systems the storage is heated when power is cheap & then used to heat water that is pumped around in a conventional central heating system when needed. In summer the heating can be done with peak day time solar & at night by wind generated electricity when demand is low.

Regards,

[Tedx]

Well given the huge amount we pay in curtailment charges, not to mention the wasted electricity, 'low grade' heating such as this, with its relative simplicity and cost effectiveness would seem for the likes of large warehouses, superstores, swimming pools? It would appear to be the way to go.

[9873210]

... a sand battery heat storage system is better than a heat pump in terms of its ability to heat a poorly insulated house in very cold temperatures where a heat pump struggles

The way to heat a poorly insulated house is to not have a poorly insulated house.

People keep trying to justify clever ways of doing things that should not be done.

Nothing against sand batteries, they can also be used to heat well insulated homes. Since they work better at larger scale they work better for district heating plants, and that requires a lot of insulation in the distribution network, may as well put some insulation in the houses as well.

[88V8]

....In heat storage systems the storage is heated when power is cheap & then used to heat water that is pumped around in a conventional central heating system when needed. In summer the heating can be done with peak day time solar & at night by wind generated electricity when demand is low.

So three inadequate systems to do what is currently done with one. Is this 'progress'?

V8

[DrFfybes]

The way to heat a poorly insulated house is to not have a poorly insulated house.

There speaks someone who I assume has never had to deal with English Heritage

[9873210]

The way to heat a poorly insulated house is to not have a poorly insulated house.

There speaks someone who I assume has never had to deal with English Heritage

The way to deal with English Heritage is not to have English Heritage.

The preservation rules are political decisions not laws of nature. Bad decisions to preserve everything old should be tackled head on. There is some good old stuff, but most old stuff is junk. Preserve the Mona Lisa, not every child's first scribble. Without selectivity in fifty years we'll be installing fake plastic pipes with steam generators to mimic condensing boiler vents on vintage houses, and Leylandii will still be a threat to civilization.

[88V8]

There speaks someone who I assume has never had to deal with English Heritage

The way to deal with English Heritage is not to have English Heritage.
The preservation rules are political decisions not laws of nature. Bad decisions to preserve everything old should be tackled head on. There is some good old stuff, but most old stuff is junk.

I am happy to pay extra to heat my C17 cottage.
Those who do not wish to undergo the slight inconveniences of living in a historic house should stick to new ones.
There is quite enough ugliness in the world without sacrificing what little beauty remains on the altar of 'efficiency'.

V8

[GrahamPlatt]

I am happy to pay extra to heat my C17 cottage.
Those who do not wish to undergo the slight inconveniences of living in a historic house should stick to new ones.
There is quite enough ugliness in the world without sacrificing what little beauty remains on the altar of 'efficiency'.

Beautiful! (the photo and the sentiments both)

[odysseus2000]

Most UK people live in homes built before good insulation was considered necessary & mandated by government, that includes most houses built before the 21st century.

To retro insulate one of these houses is a big & expensive job. Sure lofts are not too much trouble, but walls are. If there is no cavity wall then one either has to add additional internal or external insulation & that means either very expensive thin insulation or less expensive thick insulation that takes away living space.

A government could decide to force houses to be rebuilt to modern standards with grants that covered the cost and some people would like this, but many wouldn’t especially as the quality control of builders with “free money” is often poor.

The alternatives are to make the best of what one has & for many houses heat storage linked into existing central heating systems looks more practical than heat pumps. Both system reduce co2 emissions & can in the appropriate dwellings be performance & capital cost comparable to traditional gas heating systems. Storage heaters are also potentially far more reliable than modern gas boilers that come with warranties of five years & seem to fail in various ways that were impossible for older systems that in one of my houses have been installed since the early 1980’s. I doubt heat pumps will last that long, but a tank of sand with a replaceable heating element ought to see many decades of service.

As always it comes down to what folk want. Some want a throughly modern, low maintenance, low energy cost house, others want the character of an old house, with as modern services as can be added without spoiling it.

Heat storage seems a good solution for many older houses.

Regards,