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Post by dogless on Aug 7, 2023 7:30:50 GMT
I keep hearing of boaters who have LA batteries, but have added a lithium battery to the system to bolster available power usage without totally going lithium.
Can someone explain how this works please?
I understood alternators for charging lead acid batteries may burn out trying to charge lithium.
I was recently moored next to a boat that an electrical engineer was converting to lithium, and in passing he mentioned what a huge job it was ... changing cables, alternators, fusing systems and of course battery banks. He was certainly there for longer than two full days working.
So how is it possible to just 'drop-in' a lithium ?
Rog
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Post by kris on Aug 7, 2023 7:35:34 GMT
It isn’t really possible to just drop the lithium in. But basically your talking about what’s being called a hybrid system. There is a 12v boaters group on Facebook which is one of the main places promoting this way. I don’t fully understand it, but as I understand it they use thin wires (resistance.) to control the flow to the lithiums. If you go on the Facebook group there seems to be lots of people successfully using a hybrid system.
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Post by Telemachus on Aug 7, 2023 7:38:16 GMT
Generally what people are doing is to put a Li battery in parallel with a lead acid battery. Because the chemistry of the Li is different, it tends to sit at a more constant and higher voltage that the LA - during discharge, the Li remains above 13v until it is close to flat, and therefore all the current comes out of the Li and the LA remains fully charged. For recharge, people use a standard 14.4v alternator which is 3.6v/cell which is ok. If the Li battery overcharges, its internal BMS will shut it off. This “dumps” the alternator load but no worries, the LA is still in place to absorb the transient.
As you say Li does take the full alternator output until the battery is virtually full, so the alternator will overheat and fry itself in fairly short order. To get around this people use a long length of not particularly thick wire to add some resistance, so the alternator is working less hard and doesn’t overheat.
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Post by dogless on Aug 7, 2023 7:45:27 GMT
So effectively they're using the lithium battery until that flattens, then they still have their LA bank to use ?
Rog
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Post by kris on Aug 7, 2023 7:45:49 GMT
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Post by dogless on Aug 7, 2023 7:48:10 GMT
Thanks kris but the link doesn't work (I'm not a Facebook person) It was idle curiosity, that's all. Confusing as I believed lithium needed a totally different system of charging, storage etc. Rog
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Post by kris on Aug 7, 2023 7:48:53 GMT
So effectively they're using the lithium battery until that flattens, then they still have their LA bank to use ? Rog Yes but the main reason people go this way is so they don’t have to spend money on exspensive alternator regulators or battery to battery chargers.
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Post by kris on Aug 7, 2023 7:50:20 GMT
Thanks kris but the link doesn't work (I'm not a Facebook person) It was idle curiosity, that's all. Confusing as I believed lithium needed a totally different system of charging, storage etc. Rog Shame because this group is the main source of info on hybrid setups. But I can understand why you wouldn’t want to join Facebook and I applaud you for it.
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Post by Telemachus on Aug 7, 2023 7:51:05 GMT
So effectively they're using the lithium battery until that flattens, then they still have their LA bank to use ? Rog Yes, although there is a crossover period where both the LA and Li are feeding current. Li will drop below 12.7v at about 10% SoC, and then both will discharge in parallel. Ultimately Li is good down to 10v which is very flat for LA. But the general idea is to avoid this region due to the long time it takes to recharge LA.
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Post by Telemachus on Aug 7, 2023 7:55:54 GMT
Thanks kris but the link doesn't work (I'm not a Facebook person) It was idle curiosity, that's all. Confusing as I believed lithium needed a totally different system of charging, storage etc. Rog It does if you want to do it properly. These hybrid systems are a bodge, and folk may come unstuck because currently the BSS is very anti these hybrid systems. Eventually it may be a BSS fail to have Li in parallel with LA. One thing is that unlike LA, Li hates to be held up at a charging voltage so on a long cruise once the Li is charged, if the voltage remains up at 14.4v or so, the life of the Li is shortened. So if you only ever run the engine to charge the batteries or move as little as possible, then it might be ok. But on a 7 hour cruising day you would not be being kind to the Li. You could have a manual disconnect of course, or use a B2B between the LA and the Li, but B2Bs seem horribly inefficient and expensive.
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Post by dogless on Aug 7, 2023 7:57:39 GMT
Thanks.
Another stupid question.
Isn't it a bit risky to operate this system, effectively relying on thin cables to offer resistance and 'balance' things out ?
Sounds a 'bit Heath-Robinson'
Rog
ETA posted at same time as above, which really answers it 👍
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Post by kris on Aug 7, 2023 7:58:41 GMT
“Properly?”
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Post by Telemachus on Aug 7, 2023 8:01:57 GMT
Thanks. Another stupid question. Isn't it a bit risky to operate this system, effectively relying on thin cables to offer resistance and 'balance' things out ? Sounds a 'bit Heath-Robinson' Rog Definitely heath-robinson. But it does work in a crude way. I don’t think it is particularly unsafe if done properly, ie adequate fusing at the battery end. It is a blunt instrument though, you have to adjust the wire length to prevent alternator overheating in the worst case scenario, regardless of other factors such as ambient temperature, alternator fan rpm etc. A proper system measures alternator temperature and adjusts the output accordingly.
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Post by Telemachus on Aug 7, 2023 8:04:30 GMT
Properly as in having the battery BMS communicate with the charging mechanisms (alternator, mains battery charger etc), temperature regulation of the alternator, and temperature protection for the batteries to prevent charging at too low or too high temperatures. Also if you have a big alternator, a means to reduce alternator load at low rpm so the engine and drive belt don’t struggle.
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Post by dogless on Aug 7, 2023 8:07:32 GMT
Thanks.
It seems very popular at present, certainly amongst liveaboards, but I couldn't get my head around what was going on.
Unsurprising being an electrical idiot 😁
Rog
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