lithium hybrid

[dreadnought]

hi,i`m thinking of introducing a lithium battery to my battery bank,at present i have four lead acids i`m going to reduce this to two lead acids and one lithium( a hybrid system),my question is,the charging cable from my 70 amp alternator to the battery bank has to be longer and offer a certain amount of resistance can i get your thoughts on this cable size please?.many thanks

[Tony Brooks]

6 minutes ago, dreadnought said:

hi,i`m thinking of introducing a lithium battery to my battery bank,at present i have four lead acids i`m going to reduce this to two lead acids and one lithium( a hybrid system),my question is,the charging cable from my 70 amp alternator to the battery bank has to be longer and offer a certain amount of resistance can i get your thoughts on this cable size please?.many thanks

 

Unless you want to massively complicate the system, please do not try it. If you provide a suitable charging profile for the lithiums it is very likely to sulphate the lead acids and if you apply the LA charging voltage to the lithiums it is very likely to destroy them.

 

All you can do is split the bank and rewire so the LAS are supplying some of the domestic electrics and the lithiums the rest, giving two banks. Then charge the LAs as normal and use your long wire to drop the charging voltage for the lithiums. Even so you may need to manually terminate the Lithium charging when they are as fully charged as you decide to go. Solar charging may well complicate things further.

 

Save up, so the whole bank can be lithiums. Keep the start battery LA.

[MtB]

13 minutes ago, dreadnought said:

hi,i`m thinking of introducing a lithium battery to my battery bank,at present i have four lead acids i`m going to reduce this to two lead acids and one lithium( a hybrid system),my question is,the charging cable from my 70 amp alternator to the battery bank has to be longer and offer a certain amount of resistance can i get your thoughts on this cable size please?.many thanks

 

I think we need a whole lot more detail to comment sensibly.

 

What do you mean by 'lithium battery' to start with? A 'drop in' complete with BMS presumably? A link to the battery you are thinking of buying please. 

 

 

 

 

[PeterF]

Try joining the Facebook 12V boating group as they advocate this method and may provide advice. The general consensus here is that this method is not the safest. It relies on the drop in BMS isolating the battery when it is full as the lead acid charge voltage is too high. The view is that the BMS should be used not as charge control but as emergency isolation when things go wrong and have charge control by for example the correct settings in solar chargers, external alternator regulators. This way you have 2 layers of protection, a single failure will not result in battery damage. The drop in lithium hybrid method relies solely on the BMS.

[MtB]

8 minutes ago, PeterF said:

Try joining the Facebook 12V boating group as they advocate this method and may provide advice. The general consensus here is that this method is not the safest. It relies on the drop in BMS isolating the battery when it is full as the lead acid charge voltage is too high. The view is that the BMS should be used not as charge control but as emergency isolation when things go wrong and have charge control by for example the correct settings in solar chargers, external alternator regulators. This way you have 2 layers of protection, a single failure will not result in battery damage. The drop in lithium hybrid method relies solely on the BMS.

 

But we don't even know if the OP is considering using bare cells or an integrated 'drop in' LiFePO4 LA replacement battery. Or even some other sort of lithium chemistry!

 

You're right in your analysis though, it's far more elegant from an engineering design point of view to control charging externally but current thinking is integrated 'drop-in's are now so cheap nowadays it no longer matters that much if the internal BMS fails and wrecks the cells. BMS electronics are also so reliable that external alternator control is no longer worth the extra effort and cost when a long bit of wire and the old LA batt does the job perfectly well, if a bit clunkily.

 

 

[Peanut]

Unless professionally installed, it may invalidate your insurance policy. It may not bother you, but it might be as well to check.

[MtB]

6 minutes ago, Peanut said:

Unless professionally installed, it may invalidate your insurance policy. It may not bother you, but it might be as well to check.

 

Pushing back, equally it may not invalidate your insurance policy. 

 

 

[Peanut]

Which is why you need to check, though it may not bother you.

[nicknorman]

When you say “check”, I’d agree but the thing to check is your policy document. The thing not to do is to phone or write to them and ask if it’s OK. Faced with an “unknown” question, the default answer from a risk averse organisation such as an insurance company, will always be NO regardless.

[dmr]

13 minutes ago, Peanut said:

Unless professionally installed, it may invalidate your insurance policy. It may not bother you, but it might be as well to check.

 

My house dwelling mate up the road is having insulation, solar panels and a heatpump installed (for free) by a government approved professional company.

So far they have installed non breathable insulation in a house that really needs breathables, drilled through a cable and drilled through a hot water pipe...and no sign of the heatpump.   A professional is just a badly trained amateur who is getting paid?

[MtB]

11 minutes ago, nicknorman said:

When you say “check”, I’d agree but the thing to check is your policy document. The thing not to do is to phone or write to them and ask if it’s OK. Faced with an “unknown” question, the default answer from a risk averse organisation such as an insurance company, will always be NO regardless.

 

Totally agree. 

 

Any question like this once asked, will be used with glee as an excuse to demand an extra £100 (or whatever) to cover the 'increased risk'. 

 

On the other hand I remember way back in the early 1970s grafting an MG1300 engine into my Mini. The MG1300 engine was about 10% more powerful than a Mini Cooper 'S' engine and on telling my insurance company, I expected them to raise my insurance from Group 1 to Group 7 (Cooper 'S' group) and triple my premium.

 

But no, they raised it from group 1 to group 2 and asked me for about another £4. AWESOME! 

 

 

 

[ditchcrawler]

On 22/03/2023 at 22:29, Peanut said:

Unless professionally installed, it may invalidate your insurance policy. It may not bother you, but it might be as well to check.

An insurance company will say the same about Lead Acids if you contact them and tell them you want to add an extra bank