Jump to content

LiFePO4 Lithium Batteries - the lazy way


TheBiscuits

Featured Posts

1 hour ago, Naughty Cal said:

Our aim for today's outing in the van is to use as much power as possible and see if we can get ours to actually register a cycle 😀

It looks like you're putting 7 amps in by solar I assume. I'm surprised your battery only reads 13volts. That seems pretty low to me considering you're charging. Is that fairly typical? At what voltages do you have your BMS configured to disconnect (high/low)?

Link to comment
Share on other sites

9 minutes ago, auslander said:

It looks like you're putting 7 amps in by solar I assume. I'm surprised your battery only reads 13volts. That seems pretty low to me considering you're charging. Is that fairly typical? At what voltages do you have your BMS configured to disconnect (high/low)?

That's not my battery 🤣🤣🤣

 

ETA: that battery has a draw on it of 7 amps not being charged at 7 amps.

Edited by Naughty Cal
Link to comment
Share on other sites

On 18/02/2022 at 11:28, Naughty Cal said:

This is the only problem we have with our Sterling Lithium battery. It doesn't register small loads.

 

We often find after an evenings use the next morning the SOC is still showing 100% because we have only used light loads all evening.

 

Like you we just use the voltage as a rough indicator of SOC. 

 

Likewise the cycle counter is no use to man nor beast if you are only using light loads.

 

Next time we go out in the van we are going to make a conscious effort to use more power between charges.

Is your fridge the dual fuel type?

If so why not use it on DC power and only switch to gas when necessary?

Link to comment
Share on other sites

10 minutes ago, MartynG said:

Is your fridge the dual fuel type?

If so why not use it on DC power and only switch to gas when necessary?

It is gas, 240v and 12v but it only runs on 12v when the engine is running. There is no option to choose 12v with the engine turned off.

 

We are going to run the heating on a higher fan setting, leave some lights on and set both of the extraction fans running. See of we can force a cycle out of it today/tomorrow. 

13 minutes ago, auslander said:

Strange, mine shows positive amps when charging and negative when discharging.

Image2373743403137168576.jpg

Ours is definitely the other way round 🤔

Link to comment
Share on other sites

8 minutes ago, Naughty Cal said:

It is gas, 240v and 12v but it only runs on 12v when the engine is running. There is no option to choose 12v with the engine turned off.

Perhaps that could be changed so as to save some gas use while using electricity won freely from solar or when on the move . Otherwise the lithium battery seems very under utilised . 

On the other hand it sounds like you could be off grid indefinitely as far as electrical requirements are concerned.

Link to comment
Share on other sites

39 minutes ago, MartynG said:

Perhaps that could be changed so as to save some gas use while using electricity won freely from solar or when on the move . Otherwise the lithium battery seems very under utilised . 

On the other hand it sounds like you could be off grid indefinitely as far as electrical requirements are concerned.

It is an absorption fridge not a compressor fridge so running it on 12v would be unwise. 

 

In spring, summer and autumn the battery will as you say be very under utilised. Its in winter when it comes into its own. 

 

We just need to stop molly coddling it and use it more heavily, which after 13 years of nursing FLA batteries seems wrong.

 

We found last year that we really do not need to be plugged in at all with this van. 

 

ETA: we could park up and not move for as long as the gas last really. In the summer that could be months.

Edited by Naughty Cal
  • Happy 1
Link to comment
Share on other sites

23 minutes ago, Naughty Cal said:

It is an absorption fridge not a compressor fridge so running it on 12v would be unwise. 

 

In spring, summer and autumn the battery will as you say be very under utilised. Its in winter when it comes into its own. 

 

We just need to stop molly coddling it and use it more heavily, which after 13 years of nursing FLA batteries seems wrong.

 

We found last year that we really do not need to be plugged in at all with this van. 

 

ETA: we could park up and not move for as long as the gas last really. In the summer that could be months.

I have 185 watt solar on the camper it can't run the 3 way fridge they seem very power hungry on 12 volts. I have thought of changing it but it works and is in good condition so why waste money? On the move it works ok of the alternator or seems to anyway 

Link to comment
Share on other sites

26 minutes ago, peterboat said:

I have 185 watt solar on the camper it can't run the 3 way fridge they seem very power hungry on 12 volts. I have thought of changing it but it works and is in good condition so why waste money? On the move it works ok of the alternator or seems to anyway 

Our solar panel is 150w and for the majority of the year keeps up with our consumption. 

 

Don't see there is much point changing the fridge if it works for how you use it.

 

Ours is a modern Thetford 3 way and it still gobbles power on 12v. Don't see any point in changing it for a 12v compressor fridge. It doesn't really use that much gas and we have 2 big bottles to run it from.

  • Greenie 1
Link to comment
Share on other sites

On 18/02/2022 at 11:28, Naughty Cal said:

Likewise the cycle counter is no use to man nor beast if you are only using light loads.

 

You are not alone in this. I've had 4 x 138Ah Valence Lithiums since November 2019, and I don't think any of them have registered a cycle in over 2 years.

 

I use them between about 20% and 90% mainly, with the occasional 100% to reset the BMV712s, so you would have thought something would be registering a cycle now and then.

Link to comment
Share on other sites

I don't understand batteries at all, but I remember being told that a battery doesn't 'see' any incoming charge if there is a load on the battery at the time. More accurately, the battery would only see a charge if the incoming current exceeded the outgoing current, and it would only see the 'marginal' current - the difference between the two. Presumably a shunt based ammeter would also only register the difference.

 

Which raises another point - the shunt based ammeter on our boat will happily tell me it's put many tens of Ah into the batteries over the winter, which makes sense as the boat is not being used, therefore no loads, so anything the solar panels sends down the cables to the batteries is a charge. Might a BMS 'remember', or take account of, these excess amps?

 

As I said, I don't understand batteries at all, so feel free to regard the above as a load of bollo if appropriate!

Link to comment
Share on other sites

28 minutes ago, Naughty Cal said:

Don't think we will clocking up a cycle today 🤔

 

Does your fridge have an AES trigger on it?  If there's one on your solar controller as well the solar can tell the fridge to switch from gas mode to 12v mode when it's got spare electricity that isn't going into the batteries.

 

That would help you use more free sunshine and more battery cycles instead of gas to run the fridge automatically.

Link to comment
Share on other sites

That doesn't really make sense. a 3.31 cell voltage at rest does not align with 100% SoC as I understand it. I'd be expecting to see at least 3.40V if not a shade more. 

 

Therefore I conclude the Sterling app is concealing a bit of charge capacity from you.

Link to comment
Share on other sites

4 hours ago, MtB said:

That doesn't really make sense. a 3.31 cell voltage at rest does not align with 100% SoC as I understand it. I'd be expecting to see at least 3.40V if not a shade more. 

 

Therefore I conclude the Sterling app is concealing a bit of charge capacity from you.

The BMS only counts any loads over 2 amps so the SOC gauge (and cycle counter) is next to useless. 

Link to comment
Share on other sites

On 26/02/2022 at 23:10, Col_T said:

I don't understand batteries at all, but I remember being told that a battery doesn't 'see' any incoming charge if there is a load on the battery at the time. More accurately, the battery would only see a charge if the incoming current exceeded the outgoing current, and it would only see the 'marginal' current - the difference between the two. Presumably a shunt based ammeter would also only register the difference.

 

Which raises another point - the shunt based ammeter on our boat will happily tell me it's put many tens of Ah into the batteries over the winter, which makes sense as the boat is not being used, therefore no loads, so anything the solar panels sends down the cables to the batteries is a charge. Might a BMS 'remember', or take account of, these excess amps?

 

As I said, I don't understand batteries at all, so feel free to regard the above as a load of bollo if appropriate!

It depends on where the shunt is placed but since we're probably talking about one that's located on the BMS at the battery, then you're right, it will only register the excess current. If you're charging at 10 amps but drawing 15, the BMS should read a discharge of 5 amps.

Link to comment
Share on other sites

  • 1 year later...
On 18/02/2022 at 13:29, MtB said:

I've been wondering about this, as the customer's alternator is not part of the contract anyway when buying batteries.

 

Then I realised it is a simple way to head off claims that "Hey, recharging your battery overheated and destroyed my alternator"!

 

I think it's a wise guarantee policy, but for a different reason.

 

When the engine is running, the alternator is (should be) powered and the LiFePO4 would charge from it; except when they're pancake flat and don't provide 12V to energise the alternator. Folks are learning to deal with this: https://www.youtube.com/watch?v=-UjVtaDATMU "3 Ways To JUMP Start A DEAD Lithium LiFePO4 Battery FAST!".

 

That's fine until the BMS says "OK I'm done charging" and disconnects abruptly. This is the "load dump" - there was a load on the alternator and now there isn't. It was supplying many amps at 12 or 13 volts, and now it has an open circuit.

 

Alternators do not like this. They contain a lot of energy in their magnetic fields and dissipating this without a load will put up to 100V onto the "12V" system. If you want technical info, try https://electronics.stackexchange.com/questions/663570/does-car-alternator-speed-increase-during-load-dump and https://www.ti.com/lit/an/snva681a/snva681a.pdf

 

What this is likely to do is fry the BMS (and anything else connected to the 12V domestic supply that isn't built to automotive standards), because it will have a maximum input voltage. The battery I have doesn't tell what it is, but it may not be much more than 30V because the battery spec allows two 12V batteries in series.

Link to comment
Share on other sites

11 minutes ago, wakey_wake said:

 

I think it's a wise guarantee policy, but for a different reason.

 

When the engine is running, the alternator is (should be) powered and the LiFePO4 would charge from it; except when they're pancake flat and don't provide 12V to energise the alternator. Folks are learning to deal with this: https://www.youtube.com/watch?v=-UjVtaDATMU "3 Ways To JUMP Start A DEAD Lithium LiFePO4 Battery FAST!".

 

That's fine until the BMS says "OK I'm done charging" and disconnects abruptly. This is the "load dump" - there was a load on the alternator and now there isn't. It was supplying many amps at 12 or 13 volts, and now it has an open circuit.

 

Alternators do not like this. They contain a lot of energy in their magnetic fields and dissipating this without a load will put up to 100V onto the "12V" system. If you want technical info, try https://electronics.stackexchange.com/questions/663570/does-car-alternator-speed-increase-during-load-dump and https://www.ti.com/lit/an/snva681a/snva681a.pdf

 

What this is likely to do is fry the BMS (and anything else connected to the 12V domestic supply that isn't built to automotive standards), because it will have a maximum input voltage. The battery I have doesn't tell what it is, but it may not be much more than 30V because the battery spec allows two 12V batteries in series.

As I understand it, this is one of the advantages of a hybrid system of LiFePo4 with lead acid - when the LiFePo4 are full and disconnect, the alternator is kept happy with current going to the lead acid.

  • Greenie 2
Link to comment
Share on other sites

Correct, however the powers that be don’t seem to like hybrid systems and my worry is that at some point in the future they will be disallowed by the BSS.

 

In any case a lead acid battery is not the only means of absorbing the load dump, for example Sterling make a load dump absorber which I presume is just a bank of transient absorbing diodes. And also modern alternators tend to be fitted with avalanche diodes that will also absorb the worst of this transient (but it will still peak at around 30v)

 

I also maintain that a properly constructed charging system doesn’t rely on the battery’s BMS to protect it from overcharging, rather the charging system should cut off or go into a zero current float before the “ultimate protection” of the BMS shut-off kicks in. The latter is then just the emergency backup protection, not the day to day means of charge control.

  • Greenie 2
Link to comment
Share on other sites

23 minutes ago, Ewan123 said:

As I understand it, this is one of the advantages of a hybrid system of LiFePo4 with lead acid - when the LiFePo4 are full and disconnect, the alternator is kept happy with current going to the lead acid.

 

Thanks - yes I knew about that idea, I'm not sure whether I want to use it. I wanted to address the load dump aspect.

 

However I got a more serious problem before I can lithium up. Better start a new thread...

 

Link to comment
Share on other sites

15 minutes ago, nicknorman said:

Correct, however the powers that be don’t seem to like hybrid systems and my worry is that at some point in the future they will be disallowed by the BSS.

 

In any case a lead acid battery is not the only means of absorbing the load dump, for example Sterling make a load dump absorber which I presume is just a bank of transient absorbing diodes. And also modern alternators tend to be fitted with avalanche diodes that will also absorb the worst of this transient (but it will still peak at around 30v)

 

 

If I've understood it (which is by no means certain), there is a question mark over whether a B2B setup will still be acceptable under future regs, even when/if the direct parallel link via long wire gets banned. 

 

Is this the unit you were referring to?  

https://sterling-power.com/products/alternator-open-circuit-protection-device

 

The way I'm imagining it is that after say an hour of engine running the B2Bs go into float, which stops the charging almost instantly.

So the Sterling protection device soaks up the excess energy, and then the alternator effectively stops running for the rest of the cruise?  

 

The thing is, I have to keep one lead acid battery to act as a starter, so that will carry on as is. 

But for the domestic alternator, I could remove the lead acid battery, link the alternator directly to a B2B, and attach this protection device to the alternator? 

Its in a similar price range to a lead acid battery, and the lead acid battery that is fed by my domestic alternator is not in great condition. So maybe instead of replacing the lead acid as I was thinking, I can install one of these Sterling devices instead.

 

 

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.