Lithium battery install, lead-acid starter with DC-DC. Where to put solar?

[JT14]

I'm installing a single Renogy 300ah Lithium battery (with internal BMS) as the house bank on our Rival 32. Starter battery will remain as the 100ah lead-acid, with a Renogy 40A DC-DC charger between the starter and house bank. Engine alternator puts out 40A, with output regulated to 20A on the DC-DC so as not to burn the alternator out when engine is running.

We are a long-distance cruising boat, and rely on our solar panels for regeneration, therefore the low output from alternator is not too much of a concern as we spend most of our time sailing. Potentially in the future we will upgrade to a Balmar system, when the wallet allows.

Solar: We have 3 x 100W panels. Each panel has an individual MPPT, two of which are Victron (and programmable to Lithium) and one is a cheaper unit that cannot be programmed.

I'd like the starter battery to be trickle fed so when we turn the key we have a full suite of cranking amps. This lead to our thinking about MPPT placement in this setup, to gain the best regeneration potential for both banks.

Option 1: We could put all the solar MPPT's on to a common bus which feeds the starter battery, with the DC-DC charger on the same bus. The thinking here is that once the starter battery reaches 13.2V, the DC-DC will kick in and start feeding the lithium house bank. This seems simple enough, but will the internal resistance of the lead acid reduce efficiency to the lithium?

Option 2: Two 100W panels are wired to the lithium house bank, with the other 100W feeding the starter battery. This is the simplest solution I think, but we do stand to lose the extra charging capacity from the 100W panel that is reserved just for the starter battery. 3 panels take up a lot of space on our small boat and to not gain their maximum output into the lithium bank would be frustrating.

Option 3: One Victron MPPT to lithium, with two 100W wired in parallel. The other Victron MPPT with a single 100W wired to lithium. Buy a new, small panel of 20W ish, to trickle charge the starter battery with the last MPPT.

Space is a at a premium right now, and adding another panel somewhere would be tricky - but that's the only downside of Option 3.

Finally, for option 2 & 3 - when the starter reaches 13.2V, and DC-DC starts feeding the lithium bank - will this trigger the lithium MPPT's to stop charging, or can the lithium accept multiple charging sources in these cases?

Thanks in advance for your input and experience!

 

[geem]

I'm installing a single Renogy 300ah Lithium battery (with internal BMS) as the house bank on our Rival 32. Starter battery will remain as the 100ah lead-acid, with a Renogy 40A DC-DC charger between the starter and house bank. Engine alternator puts out 40A, with output regulated to 20A on the DC-DC so as not to burn the alternator out when engine is running.

We are a long-distance cruising boat, and rely on our solar panels for regeneration, therefore the low output from alternator is not too much of a concern as we spend most of our time sailing. Potentially in the future we will upgrade to a Balmar system, when the wallet allows.

Solar: We have 3 x 100W panels. Each panel has an individual MPPT, two of which are Victron (and programmable to Lithium) and one is a cheaper unit that cannot be programmed.

I'd like the starter battery to be trickle fed so when we turn the key we have a full suite of cranking amps. This lead to our thinking about MPPT placement in this setup, to gain the best regeneration potential for both banks.

Option 1: We could put all the solar MPPT's on to a common bus which feeds the starter battery, with the DC-DC charger on the same bus. The thinking here is that once the starter battery reaches 13.2V, the DC-DC will kick in and start feeding the lithium house bank. This seems simple enough, but will the internal resistance of the lead acid reduce efficiency to the lithium?

Option 2: Two 100W panels are wired to the lithium house bank, with the other 100W feeding the starter battery. This is the simplest solution I think, but we do stand to lose the extra charging capacity from the 100W panel that is reserved just for the starter battery. 3 panels take up a lot of space on our small boat and to not gain their maximum output into the lithium bank would be frustrating.

Option 3: One Victron MPPT to lithium, with two 100W wired in parallel. The other Victron MPPT with a single 100W wired to lithium. Buy a new, small panel of 20W ish, to trickle charge the starter battery with the last MPPT.

Space is a at a premium right now, and adding another panel somewhere would be tricky - but that's the only downside of Option 3.

Finally, for option 2 & 3 - when the starter reaches 13.2V, and DC-DC starts feeding the lithium bank - will this trigger the lithium MPPT's to stop charging, or can the lithium accept multiple charging sources in these cases?

Thanks in advance for your input and experience!

Put existing MPPTs to the lithium. Buy and extra one for the panel without. Buy a small DC/DC charger to keep the engine battery on float off the lithium when you are not onboard. You want the maximum amount of solar going to your lithium as they will make best use of it.

 

[sawduster]

Option 4 - Dual battery solar charger for one of the panels. A few options out there, this is the one we have and it's works well Amazon.co.uk

 

[geem]

Option 4 - Dual battery solar charger for one of the panels. A few options out there, this is the one we have and it's works well Amazon.co.uk

No good for lithium

 

[JT14]

Put existing MPPTs to the lithium. Buy and extra one for the panel without. Buy a small DC/DC charger to keep the engine battery on float off the lithium when you are not onboard. You want the maximum amount of solar going to your lithium as they will make best use of it.

OK the extra MPPT makes sense, and put all the solar power into the lithium bank. How does the extra DC-DC work though? I don't understand the mechanics of this :

Alternator -> Starter -> DC-DC -> Lithium (with all solar) -> DC-DC -> Starter battery ??

Option 4 - Dual battery solar charger for one of the panels. A few options out there, this is the one we have and it's works well Amazon.co.uk

Can you mix the charging profiles of the two different battery banks? does yours work well with lithium and lead acid/sealed?

 

[Buck Turgidson]

I think Sterling make DC-DC that works in both directions. Stick the solar on the lithium and when the house is full it will charge the starter battery. Not used one but info is on their website.
I would have chosen this if I knew about it when I was putting my system together,

 

[sawduster]

No good for lithium

OK the extra MPPT makes sense, and put all the solar power into the lithium bank. How does the extra DC-DC work though? I don't understand the mechanics of this :

Alternator -> Starter -> DC-DC -> Lithium (with all solar) -> DC-DC -> Starter battery ??


Can you mix the charging profiles of the two different battery banks? does yours work well with lithium and lead acid/sealed?

Same answer for both - it's just a solar charge controller but with two outputs. That model has four charge profiles including lifepo4 for the main battery and the second trickle charge is sla only. Other models with dual charging capability may be more suitable, haven't researched those.

Sterling also do a 1A DC DC trickle charger if you wanted to keep your three victron solar controllers for the solar.

 

[JT14]

I think Sterling make DC-DC that works in both directions. Stick the solar on the lithium and when the house is full it will charge the starter battery. Not used one but info is on their website.
I would have chosen this if I knew about it when I was putting my system together,

I'm already on the back foot as I've got a Renogy DC-DC that only charges one way. I'm hoping to make it work without spending much more money. This is a very neat solution though..

 

[PaulRainbow]

Put existing MPPTs to the lithium. Buy and extra one for the panel without. Buy a small DC/DC charger to keep the engine battery on float off the lithium when you are not onboard. You want the maximum amount of solar going to your lithium as they will make best use of it.

This, but fit a 10w panel to the engine battery, no need for a controller. No need for the second DC-DC charger.

 

[JT14]

This, but fit a 10w panel to the engine battery, no need for a controller. No need for the second DC-DC charger.

I like this solution, and was my suggested option 3 in the first post.

How will the MPPTs on the lithium side react when the starter battery is being trickle charged via solar?

Will the DC-DC feed the lithium from the starter, therefore raising their voltage and tricking the lithium MPPTs to turn off?

 

[PaulRainbow]

I like this solution, and was my suggested option 3 in the first post.

How will the MPPTs on the lithium side react when the starter battery is being trickle charged via solar?

Will the DC-DC feed the lithium from the starter, therefore raising their voltage and tricking the lithium MPPTs to turn off?

I think it will be OK, the small solar panel won't raise the engine battery voltage by much, but should keep it at a float voltage. Just set the alternator running detection above the voltage that the small solar panel keeps the engine battery at.

 

[Graham376]

We are a long-distance cruising boat, and rely on our solar panels for regeneration, therefore the low output from alternator is not too much of a concern as we spend most of our time sailing. Potentially in the future we will upgrade to a Balmar system, when the wallet allows.

How often do you run the engine? Our start battery, isolated when we're not aboard, will last several months without charging. Our panels just feed the domestic bank.

 

[JT14]

How often do you run the engine? Our start battery, isolated when we're not aboard, will last several months without charging. Our panels just feed the domestic bank.

A valid question! We have sailed over 15,000 nautical miles now without trickle charging the starter battery. Charging has only been via alternator when engine running, no problems.

However as we're installing lithium, I'd like assurance that the starter will be full(ish) when we turn the engine over. In your system can you crank the engine via lithium bank? As an aside, is your system wired via a 1/2/BOTH, or an ON/OFF isolator switch?

 

[JT14]

I think it will be OK, the small solar panel won't raise the engine battery voltage by much, but should keep it at a float voltage. Just set the alternator running detection above the voltage that the small solar panel keeps the engine battery at.

This solution seems like the best, and cheapest fit. Thanks !

 

[Graham376]

A valid question! We have sailed over 15,000 nautical miles now without trickle charging the starter battery. Charging has only been via alternator when engine running, no problems.

However as we're installing lithium, I'd like assurance that the starter will be full(ish) when we turn the engine over. In your system can you crank the engine via lithium bank? As an aside, is your system wired via a 1/2/BOTH, or an ON/OFF isolator switch?

Yes we can crank the engine from domestic bank but LA not Lithium, via 3 switches - domestic, engine or both.

 

[geem]

This, but fit a 10w panel to the engine battery, no need for a controller. No need for the second DC-DC charger.

I used to do just that but from a pure engineering perspective, I didn't like the fact that the solar would put the battery through a charge cycle every day, even though they were fully charged, when all the battery needs 99% of the time is constant float. It would be nice to see a scientific study that could compare the two for long term battery life. I have my two 12v lead acid engine batteries( wired in series for 24v) and the generator 12v battery connected to dc/dc chargers floating the batteries constantly. Occasionally, I turn them off and put them through a charge cycle. Since they very rarely see an absorption phase, there is minimal gassing of the electrolyte, so in theory, minimal water loss

 

[geem]

Same answer for both - it's just a solar charge controller but with two outputs. That model has four charge profiles including lifepo4 for the main battery and the second trickle charge is sla only. Other models with dual charging capability may be more suitable, haven't researched those.

Sterling also do a 1A DC DC trickle charger if you wanted to keep your three victron solar controllers for the solar.

Is it user configurable so you can set the voltage to exactly what you want and a 5 minute absorption period? If not, then it only has generic lithium setting, which in my experience are pretty crap.

 

[PaulRainbow]

I used to do just that but from a pure engineering perspective, I didn't like the fact that the solar would put the battery through a charge cycle every day, even though they were fully charged, when all the battery needs 99% of the time is constant float. It would be nice to see a scientific study that could compare the two for long term battery life. I have my two 12v lead acid engine batteries( wired in series for 24v) and the generator 12v battery connected to dc/dc chargers floating the batteries constantly. Occasionally, I turn them off and put them through a charge cycle. Since they very rarely see an absorption phase, there is minimal gassing of the electrolyte, so in theory, minimal water loss

The 10W panels isn't going to put much into the battery though, should just keep it from losing power.

My engine batteries get a 4A charge (at 24V) from the Multiplus, but on Sunny days the charger doesn't even come on, cloudy days like today it might come on for 30 mins, obviously more in the Winter in the UK. The generator battery is connected to a little Ctek charger (also 12V as yours is).

Not at all scientific, but lots of boats have multiple outlet mains chargers, or solar with a VSR and the engine batteries don't seem to fare to badly. My current, experimental, domestic system has 280Ah of LFP wired in series with 120Ah of LA (@24V). the LA sits at the same voltage as the LFP (obviously) but doesn't take much, if any, current, so my felling is they aren't going to appreciably suffer.

 

[JT14]

I used to do just that but from a pure engineering perspective, I didn't like the fact that the solar would put the battery through a charge cycle every day, even though they were fully charged, when all the battery needs 99% of the time is constant float. It would be nice to see a scientific study that could compare the two for long term battery life. I have my two 12v lead acid engine batteries( wired in series for 24v) and the generator 12v battery connected to dc/dc chargers floating the batteries constantly. Occasionally, I turn them off and put them through a charge cycle. Since they very rarely see an absorption phase, there is minimal gassing of the electrolyte, so in theory, minimal water loss

What are the DC-DC's charging from in this setup?

 

[geem]

The 10W panels isn't going to put much into the battery though, should just keep it from losing power.

My engine batteries get a 4A charge (at 24V) from the Multiplus, but on Sunny days the charger doesn't even come on, cloudy days like today it might come on for 30 mins, obviously more in the Winter in the UK. The generator battery is connected to a little Ctek charger (also 12V as yours is).

Not at all scientific, but lots of boats have multiple outlet mains chargers, or solar with a VSR and the engine batteries don't seem to fare to badly. My current, experimental, domestic system has 280Ah of LFP wired in series with 120Ah of LA (@24V). the LA sits at the same voltage as the LFP (obviously) but doesn't take much, if any, current, so my felling is they aren't going to appreciably suffer.

It might be interesting if insurance companies start requesting compliance with ISO or ABYC. This set up of mixed chemistries won't comply with either standard.