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Lithium Battery Charging at 13.9V from Alternator


Naughty Cal

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A quick question for you knowledgeable people if I may?

 

A bit of background first. Our van is fitted with a 3 way Thetford fridge. It runs on 12v only when the engine is running, 230v when on EHU or gas when off grid. Last year it developed a fault with the 12v input which meant we have used it most of the time on gas while the dealers waited for parts to be available to fix the fault. It is now fixed and working fine on 12v. (The fault occurred before we switched to a Lithium leisure battery and was a common, well documented fault with the PCB)

 

We have since noticed that with the fridge running on 12v the voltage at the domestic battery never rises above 13.9v even after a long four hour run.

 

Turn the fridge off and the voltage at the battery quickly rises to 14.2-14.3v so I’m pretty sure that there isn’t a problem with the alternator. (All voltages taken from the Bluetooth BMS fitted to the Lithium domestic battery.)

 

The Thetford fridge is an absorption type and according to the Thetford blurb uses about 20amps continuously so it is a heavy drain which is why it is wired to only use 12v when the engine is running. Interestingly when sat in traffic the alternator can’t keep up with the fridge and the voltage gradually starts to drop back down again.

 

So the question is will charging at 13.9v while driving damage the Lithium battery? The manufacturer suggests a charging voltage of 14.2-14.6v. When charged via the solar or the 230v battery charger it does reach between 14.2-14.4v, just not when being charged by the alternator when the fridge is running on 12v.

 

We hadn’t noticed this with the previous lead acid battery due to lack of battery monitoring and it probably goes someway to explaining why the battery didn’t last too long. The lead acid battery we replaced was about 30 months old according to the dates on it. We would have expected longer given shallow discharges and the solar panel keeping it topped up for most of the year. With how the van is set up most of the high power appliances run off gas or 230v when plugged into EHU so for 10 months of the year the battery is only subject to very shallow discharges.

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Lithium batteries don’t like to be fully charged. They like to be in a mid state of charge. The exact opposite of lead acid! So they will be quite happy at 13.9v. Happier than at 14.4! 13.9v held for a long time will get the batteries up to over 98% SoC, the only advantage of 14.4v is charging a bit quicker and the extra 2% or so, but at the expense of shorter battery life.

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1 minute ago, nicknorman said:

Lithium batteries don’t like to be fully charged. They like to be in a mid state of charge. The exact opposite of lead acid! So they will be quite happy at 13.9v. Happier than at 14.4! 13.9v held for a long time will get the batteries up to over 98% SoC, the only advantage of 14.4v is charging a bit quicker and the extra 2% or so, but at the expense of shorter battery life.

Thank you. Much appreciated.

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2 hours ago, Naughty Cal said:

A quick question for you knowledgeable people if I may?

 

A bit of background first. Our van is fitted with a 3 way Thetford fridge. It runs on 12v only when the engine is running, 230v when on EHU or gas when off grid. Last year it developed a fault with the 12v input which meant we have used it most of the time on gas while the dealers waited for parts to be available to fix the fault. It is now fixed and working fine on 12v. (The fault occurred before we switched to a Lithium leisure battery and was a common, well documented fault with the PCB)

 

We have since noticed that with the fridge running on 12v the voltage at the domestic battery never rises above 13.9v even after a long four hour run.

 

Turn the fridge off and the voltage at the battery quickly rises to 14.2-14.3v so I’m pretty sure that there isn’t a problem with the alternator. (All voltages taken from the Bluetooth BMS fitted to the Lithium domestic battery.)

 

The Thetford fridge is an absorption type and according to the Thetford blurb uses about 20amps continuously so it is a heavy drain which is why it is wired to only use 12v when the engine is running. Interestingly when sat in traffic the alternator can’t keep up with the fridge and the voltage gradually starts to drop back down again.

 

So the question is will charging at 13.9v while driving damage the Lithium battery? The manufacturer suggests a charging voltage of 14.2-14.6v. When charged via the solar or the 230v battery charger it does reach between 14.2-14.4v, just not when being charged by the alternator when the fridge is running on 12v.

 

We hadn’t noticed this with the previous lead acid battery due to lack of battery monitoring and it probably goes someway to explaining why the battery didn’t last too long. The lead acid battery we replaced was about 30 months old according to the dates on it. We would have expected longer given shallow discharges and the solar panel keeping it topped up for most of the year. With how the van is set up most of the high power appliances run off gas or 230v when plugged into EHU so for 10 months of the year the battery is only subject to very shallow discharges.

 

The LA battery in our caravan has lasted 7 years, (thats put the kiss of death on it!). Charged with fridge running whilst towing, solar, and of course 240v when on hook up. I suspect though as we spend 99% of the time on EHU when sited with the charger on, ours has had an easier life than yours.

 

When stored the solar keeps on top of the discharge from the alarm and puts some into the battery too.

 

There does seem to be a huge variation in quality of leisure batteries too.

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1 hour ago, The Happy Nomad said:

 

The LA battery in our caravan has lasted 7 years, (thats put the kiss of death on it!). Charged with fridge running whilst towing, solar, and of course 240v when on hook up. I suspect though as we spend 99% of the time on EHU when sited with the charger on, ours has had an easier life than yours.

 

When stored the solar keeps on top of the discharge from the alarm and puts some into the battery too.

 

There does seem to be a huge variation in quality of leisure batteries too.

It wasn't a brand we had heard of that came off. Platinum.

 

We figured that by switching to Lithium then it only has to last 6 years to have been better value than buying a pair of FLA batteries twice (for the same useable capacity), assuming 3 years from the FLA's which is what we seemed to get on the boat.

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Just now, Naughty Cal said:

It wasn't a brand we had heard of that came off. Platinum.

 

We figured that by switching to Lithium then it only has to last 6 years to have been better value than buying a pair of FLA batteries twice (for the same useable capacity), assuming 3 years from the FLA's which is what we seemed to get on the boat.

 

Funny enough that is the exact same make as ours. When we bought the last 'van in 2015 I didn't pay a lot of attention to what make I was buying and that is what the dealer fitted. I'd never heard of them either.

 

It was still going strong when we part exed that 'van in 2018 so I just got them to swap it over. The 'van is going in for a service next week and they do a fairly rudimentary check of the battery condition so it will be interesting to see what they say.

 

I wont worry to much if they recommend renewing.

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On 24/05/2022 at 15:13, The Happy Nomad said:

 

Funny enough that is the exact same make as ours. When we bought the last 'van in 2015 I didn't pay a lot of attention to what make I was buying and that is what the dealer fitted. I'd never heard of them either.

 

It was still going strong when we part exed that 'van in 2018 so I just got them to swap it over. The 'van is going in for a service next week and they do a fairly rudimentary check of the battery condition so it will be interesting to see what they say.

 

I wont worry to much if they recommend renewing.

We very rarely got more than 3 years from the FLA batteries fitted to the boat. The best we got was 4 years from a set of Bison batteries but they don't seem to sell those anymore. At £150 a 100ah battery (and that was the price a few years ago) they were not the cheapest but they did seem to perform well. 

 

We strongly considered just fitting a pair of FLA batteries to the van to increase the battery capacity. But in the end decided to go down the Lithium route as we would only need one battery for the same capacity and it would only have to be useable for about 5 years to be more cost effective then buying a couple of FLA's twice. 

 

As it happens with how close we are to the weight limit when fully loaded the Lithium battery was probably our best option as it has saved us a fair amount of weight.

 

With a full tank of fuel, full water and loaded up with food, clothes, 2 people and the dog we only have 100kg spare to play with!

 

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(Liam wasn't in the van when the chap too the weight so there is another 80kg to add to the weight on the slip)

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