VSR lead acid and lithium

[BOOMEL]

I have got a book called the Campervan bible and there are a couple things in it I am not sure are correct:1. the DOD on agm is 80%, I thought it was 50%

2: There are a couple of issues with VSR (voltage sensing relays). It is only possible to use one if the batteries are of the same type, so if you have a lead acid stater battery and a lithium leisure battery, it won’t be possible to use the VSR.” My understanding was that lithium was a drop in replacement (Fogstar)?

I have a RAPIDO V68 Campervan with what I believe is lead cid starter battery. Can I get your feedback?

Regards,

BOOMEL

 

[Hoovie]

I have got a book called the Campervan bible and there are a couple things in it I am not sure are correct:1. the DOD on agm is 80%, I thought it was 50%

The DOD discharge levels are all very subjective and everyone has their own ideas on this.
the "classic" opinion is 'never drop below 50%' and probably a fair guideline for basic Lead Acid batteries. If you have Lead Carbon batteries, which could be AGM or GEL, then you can drop down to a DOD of 80% (aka SOC of 20%) occasionally without any harm. I have Lead Carbon batteries and certainly would not worry about them dropping to a 70% DOD for example.
If you have standard AGM batteries, apart from being told they are no use for anything ( ), my own personal opinion is you can drop to a 60% DOD (40% SOC) without harm, but others will I am sure have other ideas

2: There are a couple of issues with VSR (voltage sensing relays). It is only possible to use one if the batteries are of the same type, so if you have a lead acid stater battery and a lithium leisure battery, it won’t be possible to use the VSR.”

I would say that initial statement is quite confusing. You can't actually use a typical VSR with a Lithium Leisure Battery regardless of what the starter battery is because the disconnect voltage (the point at which the VSR opens again) is often lower than the resting voltage of a Lithium Battery - so once closed, it will tend to stay closed, which is not the operation you want to see.
If you have a VSR and want to keep using a VSR after going Lithium, you could fit a Cyrix CT-Li. This is in effect a VSR with higher cutoff voltages (amongst a couple of other things).
To reoterate, even if you had a Lithium Starter Battery (very unlikely indeed), you still could not use a standard VSR.

My understanding was that lithium was a drop in replacement (Fogstar)?

The term "Drop in replacement" is meant to convince (con!) people into thinking all they had to do was take out the Lead Battery and drop in the Lithium in the same place and bob's your uncle. I didn't think companies were still using that term. It is inaccurate in many respects.

I have a RAPIDO V68 Campervan with what I believe is lead cid starter battery. Can I get your feedback?

Regards,

BOOMEL

 

[autorouter]

2: There are a couple of issues with VSR (voltage sensing relays). It is only possible to use one if the batteries are of the same type, so if you have a lead acid stater battery and a lithium leisure battery, it won’t be possible to use the VSR.” My understanding was that lithium was a drop in replacement (Fogstar)?

I think the issues with a VSR are much the same as with a traditional split charge relay, triggered from the D+ (engine running) signal. The VSR will turn on and connect the leisure battery to the starter battery/alternator just the same. The leisure battery will get the same treatment from the alternator as the starter battery, which presumably is a standard flooded lead-acid type.

If the alternator was like the mains EHU charger, and continued to charge for 24 hours, or indeed weeks at a time, then that would be a problem. But typically a motorhome engine won't be running for more than a few hours without a break, and the alternator starts its charge cycle all over again.

A lot of the difference between the charge profiles of flooded lead acids and other types like AGM and gel is the extended absorption time of several hours, which is unlikely to happen from the engine alternator. So mostly people tolerate the less-than-optimal charge profile, as long as there is another charger (solar, EHU) to give it the long absorption time every so often.

There are many opinions about lithium 'drop-in replacement'. The thing about lithium is that it is fine if left at less than 100% charge for long periods, unlike lead-acid-based batteries that accumulate sulfation. So if you are happy that the lithium battery never gets to above 80% or 90% then that's fine. There is a view that it's better to get a battery 10% bigger than you need, and only charge it to 90%, and it will give much longer life.

The thing they don't mention is that lithium batteries should not be charged when the temperature is below zero. However the 'drop-on replacements' mostly have a built-in Battery Management System (BMS) that prevents charging below zero. I prefer to have a charger with a temperature sensor and a 'lithium profile' that will prevent this charging, but I'm sure others disagree about that.

 

[Hoovie]

I think the issues with a VSR are much the same as with a traditional split charge relay, triggered from the D+ (engine running) signal. The VSR will turn on and connect the leisure battery to the starter battery/alternator just the same. The leisure battery will get the same treatment from the alternator as the starter battery, which presumably is a standard flooded lead-acid type.

Except when you turn off the engine, a tradional split-charge relay will disconnect, as would a VSR with Lead. But not with Lithium - the VSR remains engaged.

If the alternator was like the mains EHU charger, and continued to charge for 24 hours, or indeed weeks at a time, then that would be a problem. But typically a motorhome engine won't be running for more than a few hours without a break, and the alternator starts its charge cycle all over again.

A lot of the difference between the charge profiles of flooded lead acids and other types like AGM and gel is the extended absorption time of several hours, which is unlikely to happen from the engine alternator. So mostly people tolerate the less-than-optimal charge profile, as long as there is another charger (solar, EHU) to give it the long absorption time every so often.

There are many opinions about lithium 'drop-in replacement'. The thing about lithium is that it is fine if left at less than 100% charge for long periods, unlike lead-acid-based batteries that accumulate sulfation. So if you are happy that the lithium battery never gets to above 80% or 90% then that's fine. There is a view that it's better to get a battery 10% bigger than you need, and only charge it to 90%, and it will give much longer life.

The thing they don't mention is that lithium batteries should not be charged when the temperature is below zero. However the 'drop-on replacements' mostly have a built-in Battery Management System (BMS) that prevents charging below zero. I prefer to have a charger with a temperature sensor and a 'lithium profile' that will prevent this charging, but I'm sure others disagree about that.

 

[BOOMEL]

what happens if you put lithium 8n when you have lead acid starter and VSR?

BOOMEL

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[Hoovie]

what happens if you put lithium 8n when you have lead acid starter and VSR?

BOOMEL

Did you read my reply?

 

[BOOMEL]

Did you read my reply?

I did however would appreciate elaboration

 

[autorouter]

A VSR has a threshold, and if the input voltage rises above that it will turn on. If it's set at say 13.5V then it will only turn on when the alternator is charging the starter battery. It connects the leisure battery to the starter battery, and they both get charged.

A VSR also has a disconnect threshold, and if the voltage falls below that it will turn off. If it's set at say 13.2V then when the engine stops and the alternator stops charging, the voltage of the starter battery drops back to its resting level, and the VSR turns off.

That all works fine if the batteries are lead-acid, their resting voltages are less than the disconnect threshold. However a lithium battery resting voltage will be at least 13.5V. Since the two batteries are connected together, that voltage will also appear at the VSR input. And because it's higher than the disconnect voltage threshold, the VSR won't turn off.

I hadn't appreciated this would happen, and Hoovie explained it. It's not something you're likely to see because nobody uses VSRs with a lithium leisure battery. Although you could use a relay triggered by the D+ engine running signal, in fact it's more usual to use a proper B2B charger.

 

[Lenny HB]

DOD with a standard LA is best to keep to 50%, for AGM varies on the battery but best to keep to 50%, Gels are OK with 80%.

VSR can be a pain in the butt if you have alternative charging methods. If you have solar or a batterymaster or similar charging the starter battery. When the starter battery reaches the threshold of the VSR it will turn on creating a charging loop. VSR's are best avoided on Motorhomes.

Although suppliers say you can use their Lithium's as a drop in replacement you will never get the best out of them and without a B2B there is always a possibility you will overload the alternator and it is far better to fit a mains charger & solar regulator with the correct charging profiles.
Why bother spending all that money on Lithium and not get the best out of them and risk damage.

 

[Hoovie]

DOD with a standard LA is best to keep to 50%, for AGM varies on the battery but best to keep to 50%, Gels are OK with 80%.

VSR can be a pain in the butt if you have alternative charging methods. If you have solar or a batterymaster or similar charging the starter battery. When the starter battery reaches the threshold of the VSR it will turn on creating a charging loop. VSR's are best avoided on Motorhomes.

Although suppliers say you can use their Lithium's as a drop in replacement you will never get the best out of them and without a B2B there is always a possibility you will overload the alternator and it is far better to fit a mains charger & solar regulator with the correct charging profiles.
Why bother spending all that money on Lithium and not get the best out of them and risk damage.

You wouldn't tend to use a Battery Master or other Starter Battery Trickle Charger when you have the typical VSR fitted as it would be superfluous as the VSR would switch on anyway as they are, in the main, Bi-Directional and will activate when EITHER side reaches the threshold and the trickle charge becomes redundant. There are a couple which are not bi-directional, but very rarely seen. There is also an unusual VSR that is voltage activated BUT has a vibration sensor and will only activate in effect when the vehicle is moving or the engine is running. Rather a strange unit and again not very common thankfully!

The use of a relay instead of a B2B with a Lithium Battery is an interesting one.
Really, the Lithium Charging profile in essence is super-simple .... stop when it reaches x.xV (typically 14.2V). No floating, no multi-stage profiles, just throw current into it.
But you DO get into the potential of Alternator overloading if you are not careful as you very rightly say, and for that reason I always fit or recommend a B2B for Lithium to provide current limiting as the primary role (but also providing the right voltage to the battery. Alternators can have too high a voltage as well as too little).
Using a B2B instead of a VSR helps reduce the "you fitted a split charge and now my battery light is stuck on" calls when the alternator is on the way out or plain tired and can't cope with the extra charge current of a Leisure Battery on top!

Victron do an interesting device to manage this overload prevention by current limiting situation for their Lithium Batteries. They have a product called a Smart BMS CL12/100 (below), and part of its role is to provide "split charging" from the Alternator - and what is interesting (to me, anyway ) is the method to limit the current ....

It is fitted with a Megafuse, and the current from Alternator to Battery is actually limited by the size of the fuse to approximately 90% of the fuse rating! Fit a 100A fuse and you have a 90A charge limit. Fit a 50A fuse and you have a 45A charge limit. Pretty nifty I reckon

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[bigtwin]

Victron do an interesting device to manage this overload prevention by current limiting situation for their Lithium Batteries. They have a product called a Smart BMS CL12/100 (below), and part of its role is to provide "split charging" from the Alternator - and what is interesting (to me, anyway ) is the method to limit the current ....

It is fitted with a Megafuse, and the current from Alternator to Battery is actually limited by the size of the fuse to approximately 90% of the fuse rating! Fit a 100A fuse and you have a 90A charge limit. Fit a 50A fuse and you have a 45A charge limit. Pretty nifty I reckon

That‘s very interesting as it is akin to what is referred to as ‘the long lead’ method in a Lead Acid/LiFePO4 hybrid arrangement that is being adopted by quite a few narrowboaters. If I’ve understood it correctly, effectively, Victron are using the resistance of the fuse as the means of current limiting.

Ian

 

[Hoovie]

That‘s very interesting as it is akin to what is referred to as ‘the long lead’ method in a Lead Acid/LiFePO4 hybrid arrangement that is being adopted by quite a few narrowboaters.

Tell me more I have a Lead/Lithium Hybrid setup, but definately don't use cable gauge/length for any current limiting. Never liked that theory and - IMO - it is counter-productive (inefficient), especially in a Hybrid configuration, but maybe I am missing something?

If I’ve understood it correctly, effectively, Victron are using the resistance of the fuse as the means of current limiting.

Ian

Yes,I think so - but in a fairly precise way. I think it is a clever thing to do but a world away from "long leads".

 

[bigtwin]

Tell me more I have a Lead/Lithium Hybrid setup, but definately don't use cable gauge/length for any current limiting. Never liked that theory and - IMO - it is counter-productive (inefficient), especially in a Hybrid configuration, but maybe I am missing something?

The hybrid arrangement has a mix of lead acid batteries and LiFePO4 batteries connected directly in parallel. In order to prevent overheating of the leisure alternator (most boats have separate alternators for starter and leisure), some setups need to have the alternator cable replaced with a longer cable to add resistance to the charge circuit, and hence limit the current. In many setups, the existing alternator cable suffices (in traditional lead acid setups it is often the ability of the batteries to accept a charge current that is the limiting factor, with lithiums their low internal resistance means that they can accept more current). The lithiums in this type of setup need to have a BMS with adjustable parameters setup appropriately and the lead acid(s) in the hybrid arrangement are there to protect the alternator when the BMS disconnects the lithium(s) when they are fully charged.

I think we’ve previously touched on this in another thread some time ago?

Ian

 

[Hoovie]

The hybrid arrangement has a mix of lead acid batteries and LiFePO4 batteries connected directly in parallel. In order to prevent overheating of the leisure alternator (most boats have separate alternators for starter and leisure), some setups need to have the alternator cable replaced with a longer cable to add resistance to the charge circuit, and hence limit the current. In many setups, the existing alternator cable suffices (in traditional lead acid setups it is often the ability of the batteries to accept a charge current that is the limiting factor, with lithiums their low internal resistance means that they can accept more current). The lithiums in this type of setup need to have a BMS with adjustable parameters setup appropriately and the lead acid(s) in the hybrid arrangement are there to protect the alternator when the BMS disconnects the lithium(s) when they are fully charged.

I think we’ve previously touched on this in another thread some time ago?

Ian

I was maybe hoping for more info on how these are setup.
I still don't like the idea of in many ways using the wrong spec cables to limit current.
There could be a conversation about split charging and the same reply could be taken two very different ways ....for example ... "British Motorhomes have much too small wiring for the split charge system. German Motorhomes have proper cabling there" is a common one.
But then there is another conversation which is in many ways identical but with a reversed conclusion.... "The cabling was thinner/longer to limit the current load from the alternator". And that is ok then despite earlier being poor design?

I am yet to be convinced (and I am not saying you need to do so) that this approach used is the best way by any means. In actual fact I recently upgraded the Starter - Leisure cabling on my own Motorhome from 16mm to 35mm to improve the performance, despite having a Lead/Lithium Hybrid setup. The limiting factor is the B2B, not the cable - and you need a B2B to give the correct charging profile for the Lead side of the Hybrid Battery.
If you just have a relay and a long current-limiting cable which will also have a fair old voltage drop, I doubt if your Lead Batteries ever get a proper charge?

I don't have Lithium Batteries with adjustable parameters (I think that is a very limiting requirement TBH and locks people into choosing very specific batteries), but have what is a programmable relay with adjustable parameters between the Lead and Lithium to disconnect the Lithium at the appropriate time (It is what I call a VSDR Lithium Controller) and logically is a very simple device and means you could use any off-the-shelf Lithiums with a Lead battery setup to create a Hybrid Battery Bank.

 

[autorouter]

It seems to me there's a lot of handwaving and hocus-pocus about this long thin wire argument. Quite unnecesarily, I think. The resistance of copper wire is very predictable. For example 6mm2 is 2.85 milliohms per metre, and 16mm2 is 1.07 milliohms per metre. What would be the optimum resistance? The length and cross-section could be varied to give you any value you want, so what exactly is the best resistance value, and how would you know it's the best value anyway?

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[Hoovie]

It seems to me there's a lot of handwaving and hocus-pocus about this long thin wire argument. Quite unnecesarily, I think. The resistance of copper wire is very predictable. For example 6mm2 is 2.85 milliohms per metre, and 16mm2 is 1.07 milliohms per metre. What would be the optimum resistance? The length and cross-section could be varied to give you any value you want, so what exactly is the best resistance value, and how would you know it's the best value anyway?

The thing I don't like about that approach is the waste and the approach of using inferior products to 'fix' a problem.
but each to their own.

 

[bigtwin]

I was maybe hoping for more info on how these are setup.

Do you mean the BMS settings?

If not, then there is nothing to it other than replacing one, or more, lead acids with one, or more, LiFePO4 batteries (retaining at least one lead acid in the bank). The charge profiles on the mains charger and solar controllers remain unchanged (i.e. have a lead acid profile).

I still don't like the idea of in many ways using the wrong spec cables to limit current.

There is no suggestion that incorrectly specified cables are used; it is imperative that the cables are specified to match the maximum possible alternator output. Thereafter it’s a matter of how long, and how much resistance, is required to limit the current flow.

There could be a conversation about split charging and the same reply could be taken two very different ways ....for example ... "British Motorhomes have much too small wiring for the split charge system. German Motorhomes have proper cabling there" is a common one.
But then there is another conversation which is in many ways identical but with a reversed conclusion.... "The cabling was thinner/longer to limit the current load from the alternator". And that is ok then despite earlier being poor design?

Agreed.

In actual fact I recently upgraded the Starter - Leisure cabling on my own Motorhome from 16mm to 35mm to improve the performance, despite having a Lead/Lithium Hybrid setup.

If that was your objective then that’s a sensible modification. When I first obtained my boat I had a small problem with the alternator charging of my leisure bank. It turned out that I had a high resistance in my earth/return path. When I subsequently replaced my lead bank with a hybrid bank, the bank was demanding too much from my 110A alternator which lead me to the discovery that I had a way over-specified alternator cable at 95mm2 . After running a number of tests, this was replaced with 16mm2 cable. Conventional wisdom is that resistance is the enemy of 12V lead acid battery systems, however, in LiFePO4 systems, resistance can be your friend.

The limiting factor is the B2B, not the cable - and you need a B2B to give the correct charging profile for the Lead side of the Hybrid Battery.

On the boat hybrid systems there are no B2Bs in the system. The lead acid(s) in the bank are charged directly by the alternator in the same way as they would be in a solely lead acid bank. Since the lithiums are connected directly in parallel with the leads they, as a result of their lower internal resistance, will, effectively, consume 100% of the alternator output. Only when they are fully charged will the lead acid receive a charge (that’s not strictly the case but you get my meaning). In a hybrid system any discharge will always come from the lithiums unless either the demand is particularly high, or, if the lithiums are completely depleted in which case the leads will contribute. Consequently, the leads will rarely experience much discharge and hence have little need for charging and, in most instances, will simply be trickle charged from the lithiums.

If you just have a relay and a long current-limiting cable which will also have a fair old voltage drop, I doubt if your Lead Batteries ever get a proper charge?

The voltage drop isn’t that high otherwise the lithiums wouldn’t charge. Most of the charge going into the leads come from the directly connected lithiums.

The thing I don't like about that approach is the waste and the approach of using inferior products to 'fix' a problem.

I’m not sure that I’d consider good quality copper cable as an inferior product. The beauty of the setup is its simplicity. There are no moving parts and no electronic wizardry to go wrong.

If you’re interested to find out more, pop over to the “12 volt boating group” on Facebook where this topic seems to form the majority of the posts made.

Ian

 

[bigtwin]

It seems to me there's a lot of handwaving and hocus-pocus about this long thin wire argument. Quite unnecesarily, I think.

Agreed.

The resistance of copper wire is very predictable. For example 6mm2 is 2.85 milliohms per metre, and 16mm2 is 1.07 milliohms per metre. What would be the optimum resistance?

When I first became aware of the hybrid arrangement I wanted the answer to that question and was a little frustrated by the standard response of “suck it and see” rather than finding a more precise and theoretical response/answer. However, I ended up running a series of tests to arrive at an answer that was right for me.

The length and cross-section could be varied to give you any value you want, so what exactly is the best resistance value, and how would you know it's the best value anyway?

The simple answer to that is the one that allows a high enough percentage of the full alternator output without the alternator running at too high a temperature (this is perhaps a bigger problem on narrowboats where engine room ventilation can be quite poor and normal engine running speeds are relatively low (affecting alternator cooling)).

The following images record a series of tests that I went through to arrive at my own setup.

Ian