Alternator/lithium charging confusion

[Narrowboater]

Hello,

I have just replaced my SLA with 2 100ah Renogy Smart batteries. I wasn’t aware beforehand that there would be relationship problems between them and my alternator. I’ve been given conflicting advice about the best way to get them talking without harming each other and I wondered if anyone on here would like to either clarify the situation (or add to my confusion).

Renogy have been a little sparse with advice, initially saying I should install SLA instead of the £1200 worth of lithiums I had JUST BOUGHT FROM THEM. When pushed, they said I need to ”add a voltage breaker between the lithium battery and the charger and set the voltage to 11V”.

Other folk with lithiums have variously said to install a dump battery (or use my starter as the dump) and a b2b or, alternatively, to parallel my alternators (I have twins), use a split charger from the starter (not a voltage sensitive one) and use a simple voltage sensing relay to cut the power to the relay as soon as the volts reach 14.

I have a background in electronics but it’s 25 years ago and I’ve forgotten most of it. We also didn’t do batteries or any of this gubbins, so please use easy words. Thanks.

 

[mikefitz]

When pushed, they said I need to ”add a voltage breaker between the lithium battery and the charger and set the voltage to 11V”.

Renogy support have little technical knowledge.

The lithium batteries have BMS protection that could disconnect them from the alternator, this would destroy the alternator electrics.

You will still need a LA starter battery.

Perhaps the simplest is to have the alternators feed a single lead acid battery and use a battery to battery charger to charge the lithium.
The actual current needed will be related to the available continuous current from the alternators at low engine speeds and the recommended charge current for the lithium.

types available, ( UK)

Victron. https://www.victronenergy.com/dc-dc-converters/orion-tr-smart-non-isolated
Sterling. https://sterling-power.com/collections/battery-to-battery-chargers
Votronics. https://www.votronic.de/index.php/en/products/charging-converters
Renogy. https://uk.renogy.com/dcc50s-12v-50a-dc-dc-on-board-battery-charger-with-mppt-new-version/


suppliers.

Battery to Battery DC-DC battery chargers

Find and shop for 12V / 24V Power & Distribution 1 - Battery to Battery DC-DC battery chargers products online at everyday low prices at RoadPro

www.roadpro.co.uk

Onboard Energy

www.onboardenergydirect.co.uk

Battery to Battery Chargers

simplysplitcharge.co.uk

DC-DC Battery To Battery Chargers | 12 Volt Planet

DC to DC chargers, also known as battery to battery chargers. For charging leisure batteries in Euro 5 and 6 vehicles with smart alternators

www.12voltplanet.co.uk

The larger units from Votronics have programmable current limits that are useful to prevent alternator overload.
B to B chargers can be used in parallel for higher currents.

You could charge direct from one alternator ( keeping the other for engine LA battery and start), if:

There is a lead acid battery in parallel at the alternator feed as a 'dump' or the Sterling alternator protect is fitted.
There is sufficient cable and fuse 'volt drops' in the feed to the batteries to limit the current to a safe value for the batteries and alternator.
There is an auto or manual alternator disconnect/disable then the battery reaches target volts, say 14.2 volts.
You would not be too upset if the alternator let the smoke out.

A further option is to consider alternator control modules that can be setup for lithium charging.

Alternator Regulators-OceanPlanet Energy

The right alternator regulator is imperative for getting the fastest and most accurate charging during your engine run time. Genasun, MGDC Solutions, Balmar

oceanplanetenergy.com

Sterling Electronics in the UK offer a similar alternator control module but do not seem to have a lithium profile,

Alternator Regulators

Market leaders in power distribution for off-grid purposes. Providing class leading AC/DC and DC/DC chargers, highly customisable charge options and high performance lithium batteries. Sterling aims to be an accessible performance brand.

sterling-power.com

On my sailboat I use the BMV712 programmable voltage level setup to disable the alternator by cutting the field curent when the target charge voltage is reached.

Mike

 

[BobR]

Sterling makes an alternator protector.

https://cdn.shopify.com/s/files/1/0658/7343/files/page48_Altenators_alt_prot.pdf?796

Sorry Mike I hadn't read your post.

 

[BobR]

Nordkyn design has some good info on lithium battery banks.

 

[mikefitz]

Sorry Mike I hadn't read your post.

No problem, I type s l o w

 

[BSW_Sterling]

Hi all,

Ben from Sterling here. I'm not allowed to advertise, but I can advise.

When charging lithium from an alternator source you have to battle with the fact that both the alternator and the lithium batteries are at risk of damaging each other. The alternator can spike violently if a lithium battery is the only battery it is charging and the BMS trips to 0V (Similar to if you were to just cut the feed between an alternator and a lead-acid battery- about a 50/50 chance of blowing the alternator) and the lithium, due to its incredibly low internal resistance, is prone (and happy) to demand 100% of your alternator's output continually.

We recommend having a lead-acid starter battery, or an alternator linearisation device, that the alternator outputs to directly (to cover the voltage spike issue), and then charging the lithium battery via current limiting battery to battery chargers that are rated up to but do not exceed about 70-80% of your alternators maximum continuous output, so we can keep the output at a safe range, and within your BMS specification.

To extend Mikefitz' excellent post, our alternator regulators provide the correct voltages for lithium, but not the current control. We still recommend current controlling chargers when involving lithium and alternators.

Overall though, Mikefitz' post should give you a good grasp of what's available on the market. Only adding to it as the current aspect hadn't been mentioned.