Lithium and split charger (1 Viewer)

tkk

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I know there are theoretical reasons for not using split relay for alternator charging of LiFePO4 leisure battery., uncontrolled current and relay damage and no cut-off when battery fully charged Etc. Has anyone used it problem free for a reasonable length of time or is B2B essential?
tk
 

MichaelT

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We have used ours for 18m now, battery BMS prevent overcharge etc.
 
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Dec 31, 2021
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Have them in our adria , didnt install the b2b as it affects the fridge switchover . Upto press the solar and ne charger seem to be managing well
 
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May 7, 2016
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B2B is essential if you have a smart alternator and will optimise charging with any alternator. The charge to LiFePO4 batteries cuts off when they are full, no problem there.

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MisterB

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Have them in our adria , didnt install the b2b as it affects the fridge switchover . Upto press the solar and ne charger seem to be managing well
We have the same experience, no issues so far with no B2B added after 300AH lithium added, just relying on NE setup and solar.

I did install all the cables for a B2B just in case though ...
 
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Tombola

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I had b2b on my last 2 vans , but have held off on this Rapido, as the alternator throws constant up to 40ish amps into them and seems to wind down as they get full.
No problems yet, 2x200ah lithium, naver been completely drained though and backed up by sloar on the roof.
 
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Keeping an eyes on the ah used saturday night using the usual tv lights etc we used 20 amps, the solar soon puts that back in. Guess if you're a heavy user may be different
 
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Isn't one of the main advantages of a B2B over a split charge, when used in conjunction with lithium, the speed you can re-charge at as lithium can take in a lot higher amperage than lead acid batteries.
I know that the split charge that came with my van only charged at 10-12 A/H where as the B2B I now have charges at up to 55 A/H.
 
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tkk

tkk

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B2B is essential if you have a smart alternator and will optimise charging with any alternator. The charge to LiFePO4 batteries cuts off when they are full, no problem there.
It’s a fixed output I think. Shows leisure battery charging when engine battery shows full. Chassis is Fiat Aug 2018 build according to COC.
Btw that older thread on your relay solution to disabling split charge on engine running was great. Did you manage to preserve auto step retraction and 3 way fridge changeover to d/c with this arrangement?
tk

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tkk

tkk

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Isn't one of the main advantages of a B2B over a split charge, when used in conjunction with lithium, the speed you can re-charge at as lithium can take in a lot higher amperage than lead acid batteries.
I know that the split charge that came with my van only charged at 10-12 A/H where as the B2B I now have charges at up to 55 A/H.
True but I cant get a B2B fitter before I travel. I’m getting less adventurous with DIY these days. Had a look at starter battery and there are no obvious free terminals and having CBE system might lack the courage to mess around with it. that might change but the interim solution would be to drop one in to present system (provided I didn’t damage it , hence the question) The overcurrent thro the relay is my biggest worry as the alternator end probably has a 50A fuse, well above what the relay could handle. Posts on other threads refer to Split C Rs not having a Li profile. Do they have any specific profile. I imagined that they just directed current to either /both engine or leisure battery. But, my present knowledge base is limited so Ill probably be corrected. Grateful for all above info
 
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tkk

tkk

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I had b2b on my last 2 vans , but have held off on this Rapido, as the alternator throws constant up to 40ish amps into them and seems to wind down as they get full.
No problems yet, 2x200ah lithium, naver been completely drained though and backed up by sloar on the roof.
Is it a standard relay/DS unit or has it special heavy duty rating. CBE have a built in Split Charge relay so i cant do a lot with that
 
May 7, 2016
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It’s a fixed output I think. Shows leisure battery charging when engine battery shows full. Chassis is Fiat Aug 2018 build according to COC.
Btw that older thread on your relay solution to disabling split charge on engine running was great. Did you manage to preserve auto step retraction and 3 way fridge changeover to d/c with this arrangement?
tk
2018 Fiat will be standard alternator. Fiat were still supplying for motorhome builders without smart alternators until September 2019.

The step function and 3 way fridge continue to work as normal with my additional relay. These functions are powered by the CBE distribution unit and this stays live from the leisure battery connection, it just separates the engine battery. The original D+ connection tells the CBE unit when to allow 12V fridge operation.

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Tombola

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Is it a standard relay/DS unit or has it special heavy duty rating. CBE have a built in Split Charge relay so i cant do a lot with that
not sure Im afraid, I can take a look if you know what Im looking for
 

MisterB

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I checked my NE 237 earlier via Bluetooth app for my Fogstar battery. My battery was charging at close to 30 amps whilst driving, so I'm not sure what extra a 30amp B2B would give me?

Just boiled our first kettle of water using the battery (and inverter). It took around 2% of battery charge.

So it might work out better to use 'battery' electric to boil the kettle at times ..
 
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Thanks but do I sense you are not as convinced!
tkk I don't think there is a problem, when I fit Lithium I will try without B2B to see how it goes and add if needed. The biggest issue I and others have is the current split charging set up and how to disable it without effecting other stuff.
 

MisterB

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tkk I don't think there is a problem, when I fit Lithium I will try without B2B to see how it goes and add if needed. The biggest issue I and others have is the current split charging set up and how to disable it without effecting other stuff.
Which is what I am currently doing, so far without issues (that I am aware of of course!!) on an Adria 670 SLT on Fiat Base 2018 - if anyone can identify issues that I need to resolve them please do so as obv I don't want to create issues further down the line!
 
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tkk

tkk

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not sure Im afraid, I can take a look if you know what Im looking for
Probably standard then. Just thought you might have customised it if the relay was separate from the distribution unit. Mine is built in. What brand is it CBE/Schaudtetc. Just curious if anyone with a CBE 300 has had good outcome.

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tkk

tkk

Jun 9, 2014
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tkk I don't think there is a problem, when I fit Lithium I will try without B2B to see how it goes and add if needed. The biggest issue I and others have is the current split charging set up and how to disable it without effecting other stuff.
Likewise, I’m sure Ill disable something I want to keep if I go for B2B. I’m not even sure that a professional installer may not also as manufacturers seem to wire Step and 3-way fridge differently.
 
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tkk

tkk

Jun 9, 2014
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Which is what I am currently doing, so far without issues (that I am aware of of course!!) on an Adria 670 SLT on Fiat Base 2018 - if anyone can identify issues that I need to resolve them please do so as obv I don't want to create issues further down the line!
I’m sure you would know by now, especially if relay did not like the current size. Is it a CBE/Schaudt Distribution system. Mine is CBE. The current you are drawing is impressive. Is NE237 the brand of distribution system. I’m not familiar with it.
 

MisterB

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I’m sure you would know by now, especially if relay did not like the current size. Is it a CBE/Schaudt Distribution system. Mine is CBE
No it's an NE 237
 
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Lithium batteries have much lower internal resistance than traditional lead-acid variants. So is there a risk that it draws much higher current than the system was designed to cope with?
 

Tombola

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Probably standard then. Just thought you might have customised it if the relay was separate from the distribution unit. Mine is built in. What brand is it CBE/Schaudtetc. Just curious if anyone with a CBE 300 has had good outcome.
yes, mine i a cbe300 s , and the wires installed by Rapido certainly are beefed up compared to the weedy ones on the autotrail I gutted out before.
They are using 16mm same as I used on my last installation.
My alternator also is none smart

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May 7, 2016
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Weedy wires are a hangover from caravans. 16mm are what are needed for a proper connection between leisure and engine batteries. I wonder if the NCC has noticed that motorhomes and caravans have different requirements.
 

bigtwin

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tkk This fella seems to think it's not a problem.



Indeed, however I can’t say that his test methods were anywhere near best practice. 😳

Isn't one of the main advantages of a B2B over a split charge, when used in conjunction with lithium, the speed you can re-charge at as lithium can take in a lot higher amperage than lead acid batteries.

It is, but one of the other significant benefits is that, unlike lead acid, the last 20% of the charge process doesn’t take an inordinately long time. They will accept full charge current (be that 80A, or 20A) until they are full.

Lithium batteries have much lower internal resistance than traditional lead-acid variants. So is there a risk that it draws much higher current than the system was designed to cope with?

It is a risk and is one of the reasons that B2Bs are fitted. An alternative approach however is to ensure that the resistance in the charging path (be that via fitting a longer cable twixt alternator and the battery, or via the use of a thinner cable (noting that the cable should always be capable of handling the maximum output from the alternator)) self limits the current delivered by the alternator.

Weedy wires are a hangover from caravans.

Indeed, and I suspect that it was this that was limiting the current in the video attached earlier in this thread.

I wonder if the NCC has noticed that motorhomes and caravans have different requirements.

It wouldn’t be before time.😎

Ian
 

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