What invertor?

[merl]

It kick out about 70amps

Nice!
Does that alter much with battery SOC?
What gauge cable you using between batteries?
What length approx?

 

[Exwindsurfer]

It's about 1m from inverter to batteries and I upgraded to 70mm cable as the 35 mm was getting warm not hot just warm .Have 4 batteries I use 70mm to connect them all together the cables between the batteries are only about 350mm long

 

[merl]

It's about 1m from inverter to batteries and I upgraded to 70mm cable as the 35 mm was getting warm not hot just warm .Have 4 batteries I use 70mm to connect them all together the cables between the batteries are only about 350mm long

Cheers, what's the distance and cable gauge for the charging circuit, ie between the lithium and the cab battery/alternator?

 

[Exwindsurfer]

Possible 5m and I thinks it's 35mm cable split charger at lithium end its what Phil tells me to use as I've know idea lololol.Had this set up for about 5 years

 

[wildebus]

Possible 5m and I thinks it's 35mm cable split charger at lithium end its what Phil tells me to use as I've know idea lololol.Had this set up for about 5 years

They are good Combiners. Installed one in Raes new campervan. Not ideal for one with a smart alternator but it works fine with a simple workaround.
Those units max at 120A so sounds like you are well within the limit.

 

[merl]

Possible 5m and I thinks it's 35mm cable split charger at lithium end its what Phil tells me to use as I've know idea lololol.Had this set up for about 5 years

If you've dropped in 4X100Ah lithiums in parallel and cabled them back to the the alternator/starter battery with 35mm cable and you get a nice sensible 70A charge current it just demonstrates that burning out your typical MH alternator by dropping in a lifepo4 without a B2B isn't going to happen in reality. Much more likely to get insufficient charge current with a lithium 'drop in' and the typical cable gauge you'd experience on a standard MH.

 

[Exwindsurfer]

If you've dropped in 4X100Ah lithiums in parallel and cabled them back to the the alternator/starter battery with 35mm cable and you get a nice sensible 70A charge current it just demonstrates that burning out your typical MH alternator by dropping in a lifepo4 without a B2B isn't going to happen in reality. Much more likely to get insufficient charge current with a lithium 'drop in' and the typical cable gauge you'd experience on a standard MH.

I asked Phil about a battery to battery charger but he said I didn't need one .

 

[merl]

I've commented many times about charging lifepo4 without a B2B, I wouldn't advocate it for everyone but with the correct wiring it'll be more than adequate for many installations.
Have you ever taken the time check how the charging current changes with a heavily discharged battery, say below 20%? And again what happens re the charge current when you reach 90% capacity?
I'd expect there to be a considerable difference.

 

[Exwindsurfer]

I've commented many times about charging lifepo4 without a B2B, I wouldn't advocate it for everyone but with the correct wiring it'll be more than adequate for many installations.
Have you ever taken the time check how the charging current changes with a heavily discharged battery, say below 20%? And again what happens re the charge current when you reach 90% capacity?
I'd expect there to be a considerable difference.

ive never had the battreies down to 20% lol as for what happen at 90% ive never looked all i know it works ok with know probs.

 

[wildebus]

I've commented many times about charging lifepo4 without a B2B, I wouldn't advocate it for everyone but with the correct wiring it'll be more than adequate for many installations.
Have you ever taken the time check how the charging current changes with a heavily discharged battery, say below 20%? And again what happens re the charge current when you reach 90% capacity?
I'd expect there to be a considerable difference.

Actually, there should be virtually no difference. A lithium battery charges at full current from zero SOC all the way to 100% SOC.
If you like, I will post a graph tomorrow afternoon/evening showing the current into 2 of my Lithiums on my Motorhome and their SOC as time goes on (they are currently at 11% and will be likely close to 5% by the time I plug into the mains in the morning.
There may be some wavering as there is a 3rd LiFePO4 that the shunt is not monitoring and is a bit bigger so that could affect the line a little and there are some 12V services that have to be supplied but the basic pattern should still be clear. (I'll see if I can turn that 3rd battery off anyway?)

The current will be limited to whatever the charger can put out, but a key thing will be there will be no fluctuating input power like you would see on an alternator, so will in fact be a better indication of the actual battery charging characteristic and not skewed by a variable supply.

This is an example from a test I did a few years ago. This graph doesn't show the SOC unfortunately, but with a total of around 80Ah going into a 100Ah battery, you can imagine it started pretty low? Look at the current during the near 3 hours of charging using a 30A charger ... you would be hard pushed to find a more perfect flat line than that... a constant 30A from a 30A charger.

And that characteristic - taking as much charge as it can for the whole duration of the charge is why personally I am wary about charging a Lithium Battery, especially a large bank, via what is in essence a direct alternator connection with no limiting except from cabling and the alternator itself. IMO this is why it is such a bad idea to consider Lithium as "drop in replacements" on vans with low capacity split-charge systems as the stress potential is too large for comfort.
(Next week I am swapping out some batteries for a friends Ducato camper and I will be fitting a 200Ah Lead Carbon battery and not even considering going for Lithium for that very reason as their budget only stretches to a new battery and not any new charging system)

 

[PerNorrgren]

I’m doing up a 1993 vw t4 Autotrail Cherokee , inc replacing the entire electrical system.
I had planned on using an 20 amp dc to dc charger and 2 x 100 lithium batteries with 450 w solar and 2000w inverter.
However Black Friday and see Renology has 3000w inverters at a good price, what sort of input would I need into a 3000w inverter?
Could I run 12v ? Don’t think the old alternator which is around 65 amp output would handle any more than an 20 amp dc to dc charger?

hi, I have done just this. 2005 Autotrail Chayenne on a Fiat base.
if I may share a little of what I have done, it might help. Note, this is just my experience and I am not suggesting that this is the best thing to do, it works for me.

I removed all gas and installed 230v for all appliances like water heater, induction dual hotplate, combi oven, fridge/freezer, etc.
Installed 2x Roamer 48v 100Ah batteries.
Victron RS6000 inverter.
2 x 480W solar panels on the roof.
48v - 12v smart converter for the lights and battery charging.
Diesel air heater.
1 x 230v Air convection wall mounted electric radiator
1 x 230v Portable Air Condition
I have a portable little petrol backup generator just in case.
So what is the experience of all this? magic.
To get it all in, one of the beds was removed and the other bed changed to be a sliding out double bed and this works great for us.
Also I removed the bed on top of the cab and made it storage space.
I first had a 3000W inverter but cooking became difficult as it would overload constantly. so well worth the upgrade to the RS6000 to keep the better half happy.
I had to install a separate Victron solar charger as the RS needs more voltage to take the solar panels. in the summer these two provide enough for cooking, fridge/freezer and water heater so no other form of input has been needed. This meadn no need to have electric hookup on site so can be more flexible.
Aircondition unit bliss for the summer month to lower the temp just as you go to bed.
The electric convection element is perfect for the autumn/spring nights and I do not think I have had to use the diesel heater more than a few times. Point to note with the diesel heater is that it needs a lot of Amp of 12v to start and you need a really big cable to cope with the drop in voltage if the cable is long. If I use this type of heating more in the future I will upgrade to a 48v heater and connect it to the main tank rather than have a separate diesel tank as it can smell a little for a while when topping up the tank (in one of the outside cupboards and of course you spill a little.....) and the little pump is noisy.
Also, if I start going on longer off-grid journeys rather than using sites, then an upgraded alternator will be fitted. but for now all is just great as it is.
it literally runs itself and it is like living in a mini portable house.
But, saving the best to the last, I went to a speed shop and had the Fiat stage 1 tuned. Amazing. seems the engines are turned down drastically by default, so with an upgrade this old diesel engine was transformed. We have been up and down the French, Swiss and Italian alps and it is like riding a mountain goat. even on step clime you can change up a gear. This is probably, out of all the changes, the best one.
Happy camping.
Per Norrgren

 

[merl]

this is why it is such a bad idea to consider Lithium as "drop in replacements" on vans with low capacity split-charge systems as the stress potential is too large for comfort.

I used to think exactly the same David but I'm sure I got it wrong. Rather than thinking about the lithium battery 'sucking everything it can' and burning out/ stressing components, instead consider what happens to the voltage measured at the battery in various situations.
1, with a LA battery during it's charge cycle.
2, with a LFP battery during it's charge cycle.
Assuming we're talking about alternator charging for now:
The battery terminal voltage will be higher with the LFP battery.
The alternator voltage will remain constant and the wiring resistance will also remain constant.
Current is driven by voltage difference and circuit resistance (Ohms law)
The charge voltage of a LFP battery will be higher than a lead acid so the charge current MUST be lower.
The vans system will be less stressed with a drop in lithium because the charge current will be lower.

Because, unlike an alternator, the output voltage of a mains charger essentially isn't fixed and varies automatically to maintain the charger's maximum permissible current and this high current is maintained for a longer continuous period of time with LFP because of the 'all or nothing' charge profile of LFP AND the fact that people will tend to discharge LFP deeper than LA I agree that the van's built in mains charger would have a harder time with a drop in lithium.

 

[wildebus]

Sorry, don't agree.
All you have to consider is how it is not unusual for an alternator to fail when a split-charge system is added and the load increased.
IMO it is a bad idea to not limit the current in some way. Others can have their own opinions and that is fine.

 

[merl]

and the load increased.

Sure, I agree IF the load is actually increased. How is the load being increased though? It CAN'T be increased simply by drop in lithium David because ohms law proves that alternator current must goes down.

 

[nabsim]

Would there not be some listing by the gauge of cable used?

 

[wildebus]

Sure, I agree IF the load is actually increased. How is the load being increased though? It CAN'T be increased simply by drop in lithium David because ohms law proves that alternator current must goes down.

All I can tell you is what I see. I think you are missing a fundamental point but as I said, everyone is entitled to their own view. What I have seen tells me no thanks.
What I also think is a poor idea is using thin cabling to provide current limiting by regarding it as controlling current through resistance. That is just a problem waiting to happen.

 

[merl]

Would there not be some listing by the gauge of cable used?

Yes Neil, massively.
ONLY three things govern current.
Alternator voltage.
Battery voltage.
Wiring resistance. (This includes cable, connectors, fuses etc.)
Voltage differential (alternator voltage minus battery voltage) divided by wiring resistance (in ohms) equals current in amps. This equation is inescapable, it's a fundamental law of physics.

 

[merl]

What I also think is a poor idea is using thin cabling to provide current limiting by regarding it as controlling current through resistance. That is just a problem waiting to happen.

In a properly fitted install the wiring will already be suitable for charging a LA battery from the alternator. As I've already pointed out the higher LFP battery voltage will result in LESS current than LA so further limiting of current (by adding wiring resistance) will simply make things worse, it's not needed so it's a moot point.

 

[wildebus]

In a properly fitted install the wiring will already be suitable for charging a LA battery from the alternator. As I've already pointed out the higher LFP battery voltage will result in LESS current than LA so further limiting of current (by adding wiring resistance) will simply make things worse, it's not needed so it's a moot point.

So you are saying that if you swap a lead battery for a lithium one, the charge current will actually go down?
We'll just have to agree to disagree I think.

 

[nabsim]

Reason I asked about cable sizing is, I have actually seen 'experts' on boat forums telling people how long and extra length of cable they need to fit to stop problems.

Personally I went for a B2B for two reasons. 1 because I did not know how much spare capacity my alternator had but was fairly certain it could provide me with 30A constantly. 2 it gives a proper charge cycle.

You could get relays but I don't think that Victron Li was about when I go mine, if it was nobody was talking about it but that wouldn't limit the draw