changing camper van batteries from agm to lithium

[CurioCT]

I built my camper van solar and electric system around April 2023 diagram and photo attached.

The batteries are two 150AH lead acid (all I could afford at the time) they have had one field trip in May 2023 with a three way fridge and some led lights connected) everything worked as expected batteries charged nicely from the split charge relay (on a 100mile round trip over two days), and stayed topped up during the day from two renology 200W panels and a wanderer. Since then the van has been has not been worked on for over a year. IN that time I have intermittently switched the whole system off (isolating solar first then disconnecting batteries through a switch). recent I have have turned the whole system back on. Even in the January cloud cover (in britain) my batteries are sitting nicely 12.8v.

This was unexpected I thought they would be significantly degraded and I have been looking at the market again, now there are all sorts of lower cost LiPo batteries at significantly lower costs. But I am still left somewhat confused. about a few things. I believe my solar system and budget mppt are still sufficient. though I will need to read the instructions on whether I need to manual switch the modes to lithium this is not really a concern.

A little background, the planned usage of the system is light, a few days here and there a few times a year, as such I was planning on ignoring the 50% battery discharge limitations if I needed to and replacing the batteries as and when I needed to. That said they will only be powering LED lights, two fans, twelve volt power sockets (twin car connection and twin USB) which would mostly be used to power phones, tablets, personal battery packs) no inverter usage at all everything DC powered, potentially using a camping hook up and car battery charger where hook up are available, but mostly festival or road / off road parking. All devices / sockets are discretely wired (even lights there are no chains) more than 100M of wiring through the van, there will be connections for a water pump (10litre) to the three way fridge (but the preferred use would be gas power)

I was thinking that replacing existing batteries with a pair of 100Ah LiPo batteries would be roughly the same? but I would welcome comment from anyone that has done this?

The one thing I am really confused about is the split charge relay / DC-2-DC charger piece, I have read mixed answers on whether or not you can carry on using the split charge relay with lithium batteries obviously the DC-DC charger can be be somewhat spendy in its own right? Why do some people say you cant or shouldn't use split charge relays with LiPo? is this mostly about them not working with smart alternators? (my van does not have this)

Honestly I welcome any thoughts / experiences of doing similar?

Lastly what brought me here were the excellent battery tear down videos, what was unclear to me was the implications of these. So I have seen tear down videos where they have shown significant bulging in cells and so on or overcharge cuts outs not working, but for the average user, like myself, the implications of these are unclear? Then you consider the horror stories of chinese batteries being the cause of fires and so on? At the end of the day all the budget batteries come from china, so other than brands reviewed in this manner is there anyway for average user to determine the quality of what they have purchased on or shortly after delivery? and if there is any significant risk?

Pictures-
Electric Board front
rear of electric board
basic diagram

 

[time2roll]

For the most part I recommend installing same as the AGM. Then look for issues to resolve.

Possible issues are loading the alternator too much. If the line has a fuse it is probably fine. Possibly charging voltage is not the preferred value but usually in range is good enough.

Solar is probably fine as it should already have the equalization disabled for AGM. Need to share the available profiles for best answers.

Fire risk is very very low with LFP batteries. Usually they would need to be grossly charged out of spec or physically damaged to present an issue.

The two batteries will give same or more power than the AGM set. In time more can be added if needed without worry of mixing old and new batteries.

 

[mikefitz]

welcome comment from anyone that has done this?

If the existing batteries are OK, then with you modest use, continue using them. They should last a few years.
There are a number of possible issues with your existing system that need consideration, whilst acceptable with your existing batteries, they will need to be updated for safety if you fit lithium batteries.
Solar controller.
This is a PWM type. In general they do not have good control of the charge profile and you don't get full panel power into the batteries.
Whilst usable with lithium batteries a useful update would be a Victron Smart 100/30 -solar controller.
Split charge relay.
The Cargo relay is poor quality and marginal, even in an AGM instalation. ( you may notice it gets hot). Fortunately lead batteries tend to self limit charge current. With lithium batteries this is not the case, and the charge current is limited by circuit components between alternator and lithium battery. To prevent possible overheating of the circuits and alternator, a DC to DC charger is recomended.
The additional feature of DC to DC charging is that the charger will apply the correct charge voltage and terminate charging when the battery is full. Even with a AGM system, a battery to battery charger is recomended to correctly charge the batteries. A final point against the Cargo relay is that it may be bidirectional and feed power from the higher voltage lithium batteries to the starter battery.

Fusing and overcurrent protection.
Main battery fuse.
Idealy you need a 'master fuse' at each lithium battery positive. Under fault conditions the battery could deliver several thousand amps
Fuses have a design 'fuse' rating that's selected for the application and an interrupt rating that specifies the current that will not 'jump the gap'. For Mega fuse it's 2000 amps, ANL 2000 to 5000 amps, depending on manufacturer, MRBF 10000 amps in a 12v system. ClassT, BS88, HRC, over 20 000 amps. Suggest a MRBF ,100A, with holder at each battery positive.

Blue Sea Systems 5191 MRBF Terminal Fuse Block 30-300A

Space-saving, ingition-protected MRBF 5191 fuse block for high amperage circuits such as DC main feed, inverter, windlass, bow thruster etc. 58VDC, 300A rated.

www.12voltplanet.co.uk

System fuses and overcurrent protection.
The main fuse at 250 amps is unnessarly high. Note the fuse does not suddenly fail at 251 amps, it needs over 500 amps to fuse within seconds and will pass 350 amps for many 10s of minutes , suggest 100 amps.
Your circuit has a number of low cost breakers, there are unreliable, have volt drops, trip at under or over the the design rating , and have been known to melt and cause fire. With your low power requirements the may not show issues, but under short-circuit failures may not protect. A economic solution is the fit a distribution fuse block close to the positive buss bar. The breaker on the solar feed is not needed.

Mega & Midi Fuse Power Distribution Box

Compact power distribution & fuse box that distributes power theough a single mega link fuse into 4 midi or strip link fuses.

www.12voltplanet.co.uk

Note a wiring error, not uncommon, is to feed a fuse or breaker with an undersized wire. Note the three breakers cables from the positive buss bar are only protected by the 250 amp ANL fuse.


The fire risk with lithium not greater than AGM, if the system built to best practice with quality parts , correct cable and suitable over current protection.

battery tear down videos, what was unclear to me was the implications of these

Folk want to know if the batteries are worth buying. Poor construction, batteries not meeting specification, important are the capacity and protection functions. Since charging at low temperature can damage the battery, low temp protection , if specified, can be evaluated.

 

[CurioCT]

If the existing batteries are OK, then with you modest use, continue using them. They should last a few years.
There are a number of possible issues with your existing system that need consideration, whilst acceptable with your existing batteries, they will need to be updated for safety if you fit lithium batteries.
Solar controller.
This is a PWM type. In general they do not have good control of the charge profile and you don't get full panel power into the batteries.
Whilst usable with lithium batteries a useful update would be a Victron Smart 100/30 -solar controller.
Split charge relay.
The Cargo relay is poor quality and marginal, even in an AGM instalation. ( you may notice it gets hot). Fortunately lead batteries tend to self limit charge current. With lithium batteries this is not the case, and the charge current is limited by circuit components between alternator and lithium battery. To prevent possible overheating of the circuits and alternator, a DC to DC charger is recomended.
The additional feature of DC to DC charging is that the charger will apply the correct charge voltage and terminate charging when the battery is full. Even with a AGM system, a battery to battery charger is recomended to correctly charge the batteries. A final point against the Cargo relay is that it may be bidirectional and feed power from the higher voltage lithium batteries to the starter battery.

Fusing and overcurrent protection.
Main battery fuse.
Idealy you need a 'master fuse' at each lithium battery positive. Under fault conditions the battery could deliver several thousand amps
Fuses have a design 'fuse' rating that's selected for the application and an interrupt rating that specifies the current that will not 'jump the gap'. For Mega fuse it's 2000 amps, ANL 2000 to 5000 amps, depending on manufacturer, MRBF 10000 amps in a 12v system. ClassT, BS88, HRC, over 20 000 amps. Suggest a MRBF ,100A, with holder at each battery positive.

Blue Sea Systems 5191 MRBF Terminal Fuse Block 30-300A

Space-saving, ingition-protected MRBF 5191 fuse block for high amperage circuits such as DC main feed, inverter, windlass, bow thruster etc. 58VDC, 300A rated.

www.12voltplanet.co.uk

System fuses and overcurrent protection.
The main fuse at 250 amps is unnessarly high. Note the fuse does not suddenly fail at 251 amps, it needs over 500 amps to fuse within seconds and will pass 350 amps for many 10s of minutes , suggest 100 amps.
Your circuit has a number of low cost breakers, there are unreliable, have volt drops, trip at under or over the the design rating , and have been known to melt and cause fire. With your low power requirements the may not show issues, but under short-circuit failures may not protect. A economic solution is the fit a distribution fuse block close to the positive buss bar. The breaker on the solar feed is not needed.

Mega & Midi Fuse Power Distribution Box

Compact power distribution & fuse box that distributes power theough a single mega link fuse into 4 midi or strip link fuses.

www.12voltplanet.co.uk

Note a wiring error, not uncommon, is to feed a fuse or breaker with an undersized wire. Note the three breakers cables from the positive buss bar are only protected by the 250 amp ANL fuse.
View attachment 270460

The fire risk with lithium not greater than AGM, if the system built to best practice with quality parts , correct cable and suitable over current protection.


Folk want to know if the batteries are worth buying. Poor construction, batteries not meeting specification, important are the capacity and protection functions. Since charging at low temperature can damage the battery, low temp protection , if specified, can be evaluated.

Thank you for your detailed response, most useful, I will implement the changes you have suggested. The 100amp ANL's are already on order.

Certainly I did not know that fuses had such massive tolerances, and have assumed they would blow quickly at or near the rating, that was something of a scary revelation 10 minutes at those kind of currents! As you can probably tell the whole thing was built on a pretty limited budget.

When you are talking about the wire rating from the bus bars, you mean the three wires from my positive bus bar to the three circuit breakers (which I should replace as suggested) you suggest this because that wire rating should reflect the potential for current up from the batteries rather than the potential load from the devices supported upstream on the breaker/fuse?

Also did you have any thought on how a layman with say just a multimeter and DC charger could assess the approximate quality of a delivered budget LiPo battery? (not that I am rushing to buy now given your and other responses and the general price direction over time).

 

[CurioCT]

For the most part I recommend installing same as the AGM. Then look for issues to resolve.

Possible issues are loading the alternator too much. If the line has a fuse it is probably fine. Possibly charging voltage is not the preferred value but usually in range is good enough.

Solar is probably fine as it should already have the equalization disabled for AGM. Need to share the available profiles for best answers.

Fire risk is very very low with LFP batteries. Usually they would need to be grossly charged out of spec or physically damaged to present an issue.

The two batteries will give same or more power than the AGM set. In time more can be added if needed without worry of mixing old and new batteries.

thank you for your response

 

[mikefitz]

about the wire rating from the bus bars, you mean the three wires from my positive bus bar to the three circuit breakers (which I should replace as suggested) you suggest this because that wire rating should reflect the potential for current up from the batteries

Yes, it's the batteries that have the power to overload the cable. If its a very short cable then the risk is low. Understand. when I suggest there are issues, I need to 100% on the side of safety. So it may seem you have real serious issues, when in practice, it's a low risk situation.

charger could assess the approximate quality of a delivered budget LiPo battery? (

The Internet is a good source of information on the build quality with battery reviews, although these rarely show battery performance a year later. The prices have been steadily falling and the build quality is improving but I suspect in the UK we will reach a price limit.
The additional features will be added, such as, Bluetooth, self heating, better BMS, to the low cost batteries, as these extras are very low cost to the manufacture. At the moment Amazon UK has Ecoworthy and DC House brand 100Ah at £165 , (200$ US) including sales tax (
20%VAT) and delivery.
You can test the capacity with the battery monitor.

 

[CurioCT]

Yes, it's the batteries that have the power to overload the cable. If its a very short cable then the risk is low. Understand. when I suggest there are issues, I need to 100% on the side of safety. So it may seem you have real serious issues, when in practice, it's a low risk situation.

The Internet is a good source of information on the build quality with battery reviews, although these rarely show battery performance a year later. The prices have been steadily falling and the build quality is improving but I suspect in the UK we will reach a price limit.
The additional features will be added, such as, Bluetooth, self heating, better BMS, to the low cost batteries, as these extras are very low cost to the manufacture. At the moment Amazon UK has Ecoworthy and DC House brand 100Ah at £165 , (200$ US) including sales tax (
20%VAT) and delivery.
You can test the capacity with the battery monitor.

Thank you once again