Lithium 'drop in' replacement without B2B

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Bannister99

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Just been watching this video from a UK Lithium supplier where they fit a lithium battery to a modern Swift motorhome (with a Sargent EC651 system) and do not use a B2B charger, but rely on the cable resitance between the alternator/vehicle battery and the leisure battery to keep the current down at a safe level.

Seems logical and I wondered if anyone has tried this solution?

 
Bannister99 said:
but rely on the cable resitance between the alternator/vehicle battery and the leisure battery to keep the current down at a safe level
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I've not watched the video.. but that isn't a satisfactory solution..
High resistance in the cabling will just dissipate as heat..
The need for a battery to battery with its larger cable size ..or increasing the cable size of the existing wiring from the alternator to the leisure battery is the way to go.. but the second option does not protect the alternator at high load and low revs when it will struggle to keep cool enough..
Andy
 
Hi Andy,

It's worth watching the video as he uses a completely flat lithium battery, so it's a worse case scenario test and it draws less that 20amps which is well within the cables capacity and hence no heat would be disipated and there's no stress on the 150A capability of the alternator.
 
Bannister99 said:
Hi Andy,

It's worth watching the video as he uses a completely flat lithium battery, so it's a worse case scenario test and it draws less that 20amps which is well within the cables capacity and hence no heat would be disipated and there's no stress on the 150A capability of the alternator.
Click to expand...
Yes, increasing the size of the cables would be risky, as it would increase the current. You will have the wear effect of using a dumb charger. Eventually, the dumb alternator will be dumping 14.4V constant voltage, which will cause wear on long journeys. A better storage voltage for lithium is 13V.
 
cmcardle75 said:
Yes, increasing the size of the cables would be risky, as it would increase the current. You will have the wear effect of using a dumb charger. Eventually, the dumb alternator will be dumping 14.4V constant voltage, which will cause wear on long journeys. A better storage voltage for lithium is 13V.
Click to expand...
That's a good point - I didn't think about the battery being potentially over charged 🤔
I would ordinary go with a proper B2B charger, but having a Sargent system already with built in split charge relay makes this difficult. I can't just remove the vehicle battery connector as it's also used to supply my 3-way fridge when the engine is running.
 
Bannister99 said:
That's a good point - I didn't think about the battery being potentially over charged 🤔
I would ordinary go with a proper B2B charger, but having a Sargent system already with built in split charge relay makes this difficult. I can't just remove the vehicle battery connector as it's also used to supply my 3-way fridge when the engine is running.
Click to expand...
To be fair, with small enough wiring, it won't be very bad for the Lithium unless you do lots of wiring. However, they are expensive and it seems strange to spend a fortune on batteries and then potentially destroy them unnecessarily. You'd certainly want to check the actual charging currents and voltages to be aware of what is actually being delivered. You could even stick a switch in to manually stop charging when they're full.
 
I think he has missed the point in respect of the BMS as it is designed to cut out in low temperatures etc.

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Bannister99 said:
That's a good point - I didn't think about the battery being potentially over charged 🤔
I would ordinary go with a proper B2B charger, but having a Sargent system already with built in split charge relay makes this difficult. I can't just remove the vehicle battery connector as it's also used to supply my 3-way fridge when the engine is running.
Click to expand...
When I fitted a B2B charger to my MH with a Sargent charger, I installed a relay that disconnects the Alternator to Leisure Battery connection when the engine is started. The fridge is on a separate circuit. In fact, I used the +ve supply to the fridge to energise the relay.
 
Revolvor said:
When I fitted a B2B charger to my MH with a Sargent charger, I installed a relay that disconnects the Alternator to Leisure Battery connection when the engine is started. The fridge is on a separate circuit. In fact, I used the +ve supply to the fridge to energise the relay.
Click to expand...
Great idea - Sounds like a good solution to ensure a B2B would do it's job correctly and not be bridged by the split charge side.
stevewagner said:
I think he has missed the point in respect of the BMS as it is designed to cut out in low temperatures etc.
Click to expand...
I believe the battery he's using already has this built in.
 
Revolvor said:
When I fitted a B2B charger to my MH with a Sargent charger, I installed a relay that disconnects the Alternator to Leisure Battery connection when the engine is started. The fridge is on a separate circuit. In fact, I used the +ve supply to the fridge to energise the relay.
Click to expand...
That’s exactly what we want to do but we don’t know how as can’t find any photos or videos to show how it’s done ie idiots guide!
 
HectorsHoose said:
That’s exactly what we want to do but we don’t know how as can’t find any photos or videos to show how it’s done ie idiots guide!
Click to expand...
These two posts explain what I did:

Post in thread 'Installing Victron B2B charger' https://www.motorhomefun.co.uk/forum/threads/installing-victron-b2b-charger.237284/post-4509077

Post in thread 'Installing Victron B2B charger' https://www.motorhomefun.co.uk/forum/threads/installing-victron-b2b-charger.237284/post-4510805

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HectorsHoose said:
Thankyou!
Click to expand...
Just looked at what you did. Unfortunately ours is the EC500 Sargent PSU with the EM40 & the wiring is different, we have the wiring diagrams so need to compare them with the EM50 diagram & see if we can work it out 🥴🤔
 

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