Lithium battery conversion

[Trident]

Its only a rough rule of thumb but aim for 1 amp per cc of engine so a common 3GM30 would want 950 amps though the manual suggests 800
So 4 of the Renogy batteries linked above would do the job in parallel. I can get them trade at £599 so if you'd like to spend £2400 for 800ah of battery I'll be happy to help you out.

For half that you could build a 900 ah pack from EVE cells with 3 BMS and as noted above start the engine direct from the cells with no BMS - in fact in an emergency one pack at 280 ah would do it

With regard to rogerthebodger's question - you could have a switched negative lead direct from the battery pack negative that bypasses the BMS and would feed power direct from the cells. This could be opened by a simple rotary switch so that you could manually bypass the BMS. You could also have it on an always open solenoid powered from the BMS feed so that if that fails the solenoid would close the switch and you make the new circuit. The issue with that is of course why did the BMS fail? If it automatically triggers a bypass why have it at all. A manual switch at least lets you decide if a nav light or an engine start is needed immediately to save the vessel and weigh that risk against a battery fault

 

[gregcope]

My JDB SP04S034 200A BMS will deliver (according to the datasheet);

210-250A for upto 15-25secs before a Primary discharge overcurrent protection current kicks in.

400-480A for upto 150-500mSecs before a Secondary discharge overcurrent protection current kicks in.

I have these on a 350A fuse.

I have not tested these, but have started the engine off it so would assume it can deal with engine start current spikes.

My point is that a some/most mosfet BMSes can deliver over their rated nominal current for short periods like an induction start load spike.

 

[jac]

No, the battery you linked to won't work as an emergency start battery, unless it's a very small engine, as it's limited to 200a. Plus, it's expensive.

If you fitted one of the LifeP04 packs we are discussing here, with a bog standard LA battery in parallel, you can start the engine from that. Plus. the LA battery protects you from a BMS shutdown for any reason. It also protects your alternator from shutdowns and from the LifeP04 trying to run the alternators at high output for extended time.

There are other ways to achieve the above, of course.

I'm confused

The manual for my MD2030 says that the starter motor draws 100A. Why would a battery where the BMS states 200A continuous draw and 270A for 30 seconds not work?

 

[PaulRainbow]

My emergency switch is connected to the engine switch load terminal and the domestic load terminal.

If the engines didn't start, turn the switch and jump them from the domestic bank, which would work for me as i have 2 x LA in series, paralleled to the Lithiums.

If the BMS shut down the LA would run the domestics. If both failed (virtually impossible) the emergency switch allows everything to run from the engine batteries.

 

[PaulRainbow]

I'm confused

The manual for my MD2030 says that the starter motor draws 100A. Why would a battery where the BMS states 200A continuous draw and 270A for 30 seconds not work?

Did you miss the "unless it's a very small engine" ?

 

[jac]

Its only a rough rule of thumb but aim for 1 amp per cc of engine so a common 3GM30 would want 950 amps though the manual suggests 800
So 4 of the Renogy batteries linked above would do the job in parallel. I can get them trade at £599 so if you'd like to spend £2400 for 800ah of battery I'll be happy to help you out.

For half that you could build a 900 ah pack from EVE cells with 3 BMS and as noted above start the engine direct from the cells with no BMS - in fact in an emergency one pack at 280 ah would do it

With regard to rogerthebodger's question - you could have a switched negative lead direct from the battery pack negative that bypasses the BMS and would feed power direct from the cells. This could be opened by a simple rotary switch so that you could manually bypass the BMS. You could also have it on an always open solenoid powered from the BMS feed so that if that fails the solenoid would close the switch and you make the new circuit. The issue with that is of course why did the BMS fail? If it automatically triggers a bypass why have it at all. A manual switch at least lets you decide if a nav light or an engine start is needed immediately to save the vessel and weigh that risk against a battery fault

Isn;t the 3GM more like 1000 Watts? - so about 80-85 Amps?

 

[jac]

Did you miss the "unless it's a very small engine" ?

I wouldn't say it's very small - Standard fit on a 36 foot boat. Same starter on MD 2040 IIRC which would be more like a 38.

 

[PaulRainbow]

I wouldn't say it's very small - Standard fit on a 36 foot boat. Same starter on MD 2040 IIRC which would be more like a 38.

My engines would "trip" a 200a BMS in a millisecond.

If you want to fit an expensive so called "drop in" battery to start your engine, don't let me stop you, but there are several better alternatives detailed in this thread.

 

[jac]

My engines would "trip" a 200a BMS in a millisecond.

If you want to fit an expensive so called "drop in" battery to start your engine, don't let me stop you, but there are several better alternatives detailed in this thread.

I assume you have bigger engines!

I Don't want one to start my engine. I'll carry on using a LA engine start battery for that. But when i change my current LA domestic bank to Lithium this winter I still need to have a way of starting should the engine start battery fail. With the current 2 LAs i simply have a separate isolator that i can turn and can start from domestic. if a new Lithium can start the engine like that then fantastic - i don;t need another emergency solution.

It it won't then i do.

What I'm reading is that albeit said Renogy battery is expensive, there is no reason why it couldn't do the job. the challenge is now finding a cheaper good quality battery. The Eve cells do look like a good option - hadn't seen them before and if they can provide a BMS that sustains 200a ( or even 100a ) then that should be fine.l

 

[PaulRainbow]

I assume you have bigger engines!

Yes

I Don't want one to start my engine. I'll carry on using a LA engine start battery for that. But when i change my current LA domestic bank to Lithium this winter I still need to have a way of starting should the engine start battery fail. With the current 2 LAs i simply have a separate isolator that i can turn and can start from domestic. if a new Lithium can start the engine like that then fantastic - i don;t need another emergency solution.

If your starter really only draws 100a then you should be fine for an emergency start, as long as the BMS is more than 100a. Fit a 300a BMS for good measure.

It it won't then i do.

What I'm reading is that albeit said Renogy battery is expensive, there is no reason why it couldn't do the job. the challenge is now finding a cheaper good quality battery. The Eve cells do look like a good option - hadn't seen them before and if they can provide a BMS that sustains 200a ( or even 100a ) then that should be fine.l

EVE cells with a JK BMS, which you can get 200a or 300a. See one of my earlier posts for a link to a 300a JK BMS

 

[Neeves]

You can source cheap, its all relative , jump start emergency battery devices (that offer emergency lights, warning lights and sufficient power to inflate a small dinghy (and start a bigger diesel engine than most of us have on our yachts) - all lithium storage. If the question is 'emergency' only - then surely these will suffice to replace a failure of a LA bank (to start an auxiliary engine). You are relying on Lithium but not a Lithium house bank with its inherent BMS restrictions. Once the engine is running the jump start can be re-charged (if you have the facility to plug the jump start into your system).

Unless I have missed something it seems a cheap option to add to the debate and mix.

Chosen at random, its from Temu (prices in A$), but Halfords will have something similar

Temu | Explore the Latest Clothing, Beauty, Home, Jewelry & More

We used one when the battery on our new car failed (replaced under warranty) and they work as defined on the box.

They may not be suitable if you have a 100hp marine diesel - I'm thinking something smaller. They won't, or course, retreive the anchor - but they might start the engine.

Jonathan

 

[geem]

My engines would "trip" a 200a BMS in a millisecond.

Ditto. My 4.4L engine uses a 7kw starter motor

 

[geem]

You can source cheap, its all relative , jump start emergency battery devices (that offer emergency lights, warning lights and sufficient power to inflate a small dinghy (and start a bigger diesel engine than most of us have on our yachts) - all lithium storage. If the question is 'emergency' only - then surely these will suffice to replace a failure of a LA bank (to start an auxiliary engine). You are relying on Lithium but not a Lithium house bank with its inherent BMS restrictions. Once the engine is running the jump start can be re-charged (if you have the facility to plug the jump start into your system).

Unless I have missed something it seems a cheap option to add to the debate and mix.

Jonathan

There are some very good emergency capacitor start packs about now that would start a diesel engine for not a lot of money. You can connect them to a flat battery, wait a few seconds whilst they energise and off you go. They would be a good back up for lots of people regardless of lithium or not

 

[Neeves]

There are some very good emergency capacitor start packs about now that would start a diesel engine for not a lot of money. You can connect them to a flat battery, wait a few seconds whilst they energise and off you go. They would be a good back up for lots of people regardless of lithium or not

I have noted that the biggest fear that has developed over a Lithium installation is the concern that the LA starter battery might fail. Oddly this is the common fear - maybe we have lived a charmed life and this would be low down my questions.

But these cheap jump starts seem to answer the issue.

Now which are the best to buy - don't know but they seem to be easily available.


As Geem says - they are worth having. I'm not sure the emergency lights would be a big feature for us - but would take the agro out of inflating a dinghy, are pocket sized (unless you have (as I do) Scots pockets) and might start the engine - I wait qualification and critical comment (to anything I post) from the sparkies.

Jonathan

 

[geem]

I have noted that the biggest fear that has developed over a Lithium installation is the concern that the LA starter battery might fail. Oddly this is the common fear - maybe we have lived a charmed life and this would be low down my questions.

But these cheap jump starts seem to answer the issue.

Now which are the best to buy - don't know but they seem to be easily available.


As Geem says - they are worth having. I'm not sure the emergency lights would be a big feature for us - but would take the agro out of inflating a dinghy, are pocket sized (unless you have (as I do) Scots pockets) and might start the engine - I wait qualification and critical comment (to anything I post) from the sparkies.

Jonathan

There are different types of jump start units. Some of just capacitors. They are for jump start only. Some also contain a lithium battery. You need to make sure you get the one that fits the purpose

 

[Neeves]

There are different types of jump start units. Some of just capacitors. They are for jump start only. Some also contain a lithium battery. You need to make sure you get the one that fits the purpose

Ours has a Lithium battery - I did not know there was an 'option'. I assume that the multi purpose, jump start, pump (dinghy, tyres), 'torch' and flashing lights (so warning) are the ones on which to focus.

Its maybe an area for PBO to centre some investigation (it would be an extraordinarily cheap survey) - given that they (PBO) may answer the most common fear for a lithium battery bank conversion. No point in I, nor Thinwater, having a look - availability to us is insufficiently UKcentric.

Jonathan

 

[Trident]

I based my figures on the CCA recommended by the manufacturer not the starter motor wattage . You then have to allow losses in the wiring and relays and that you may be trying to start in minus 5 whist also running the electrics so I wouldn't base things solely on the 1000 watt starter motor value.

 

[Trident]

What I'm reading is that albeit said Renogy battery is expensive, there is no reason why it couldn't do the job. the challenge is now finding a cheaper good quality battery. The Eve cells do look like a good option - hadn't seen them before and if they can provide a BMS that sustains 200a ( or even 100a ) then that should be fine.l

The Renogy is one of the best (I have been installing them for years and still do for many cases) and if you're happy with it then its not expensive other than when compared to building your own pack - but even then when you consider that you need to get a stable voltage supply unit to top balance the pack, a way to give compression to the pack etc, its not really all that much cheaper but you'd get 280ah not 200. [Inappropriate quoted content removed]

The BMS on the Renogy is great, not as informative as the JK , but it's high quality and they use the right size leads internally to allow that full 200a discharge which is where many cheaper brands fail - 200a BMS but 10mm2 wires to try and handle it

EVE cells will work out cheaper but you do need to balance them with a fixed supply, you need to do a bit of wiring (making battery leads and attaching terminals to the balance wire - all straightforward) and if you don't already have the equipment then the cost is probably the same

 

[Sea Change]

The extra cost to assemble your own battery really isn't all that much.
My bench top power supply was less than £50 and it's been very handy for other things too- e.g. I'm now using it as a battery charger for my Lidl cordless tools after the genuine charger died.
The materials to build the compression case don't have to be expensive either. £5 for some threaded rod from Toolstation, and some scrap ply for the end plates. On my first battery I used aluminium, because I'd found a road sign in a ditch

 

[Trident]

The extra cost to assemble your own battery really isn't all that much.
My bench top power supply was less than £50 and it's been very handy for other things too- e.g. I'm now using it as a battery charger for my Lidl cordless tools after the genuine charger died.
The materials to build the compression case don't have to be expensive either. £5 for some threaded rod from Toolstation, and some scrap ply for the end plates. On my first battery I used aluminium, because I'd found a road sign in a ditch

Indeed - in fact most people now are just using fibre tape for the compression which works perfectly for a few quid a roll. But its worth noting that additional costs are incurred - not everyone will already own crimping tools etc as well as the power supply. When making a comparison it is best to give all the facts.

I am all for building packs - I do at least one every week and sometimes as many as 4 . The biggest issue people will face is the time to top balance their battery pack. A stable supply for £50 as you note , will only be 10amp and so running 4 cells from perhaps 40% full to 100% full can take days. I tend to use a 30 amp supply with the cells in series at 14v to go up to about 90% and then swap to the bench supply and reconfigure to parallel to top balance at 3.6v - even so in a week when I have lots to make the charging is happening continuously from dawn til dusk.

It is all straightforward to do but not everyone wants to spend the time or trust their own electrical skills so the "drop in" option is still popular and better for some.