WIth regards to installing a hybrid-lithium bank with a single alternator engine.

[Tasemu]

I ran into an interesting issue recently when I was installing a lithium battery into a friends boat. He wanted to go hybrid which didn't seem a problem to me at the time. The thought process we came up with was as follows:

 

Alternator -> Starter Battery -> VSR -> Lithium

 

The logic being that the engine will use the starter battery to crank until the alternator kicks in and the starter battery voltage rises. This then activates the the VSR and parallels it with the lithium bank. When the engine is stopped then the starter voltage will drop and disconnect the VSR. What we didn't realise is that the VSR units don't only detect one side for disconnection. so while cranking worked fine, once the engine was stopped the lithium bank and even the solar was propping up the starter voltage through the VSR. As such we were uncomfortable trying to crank the engine again with the lifepo4 bank paralleled.

 

I've seen plenty of hybrid setups on dual-alternator systems utilising lead acid leisure batteries in parallel with lithium, but haven't seen much in the say of a single alternator system using the hybrid model. They tend to use B2B chargers. My question is: Is this the reason why? Or is there a modification I can make to this that i'm missing?

 

Thanks in advance for any and all advice!

 

EDIT 1: We are also using a BMS configured for a hybrid setup to ensure no mistreatment of the lithium battery while on charge.

Edited February 9, 2023 by Tasemu

[Tony Brooks]

Originally non-bi-directional VSRs were available, they may still be. However, I am not sure of the wisdom of charging a lithium in that way because of the need for a different charging profile and the need to shut the charging down to prevent damage.

[BEngo]

Not all VSR's are dual sensing. If you find a single sense one, and connect it right the Li will be disconnected when the alternator shuts down.  It will not cure the problem of possible overcharging of the Li.

 

Single alternator with B2B is there to avoid floating the Li at excessive voltages and overcharging it.   

 

In a 12V set up. Once the Li is fully charged at about 3.64 V per cell and the voltage is the same across all the cells in the pack (top balanced)  you want to STOP charging entirely.   Holding the battery at 14.6v or more when full  causes it to carry on trying to charge and is  * bad*  for the Li.   So the B2B is brought in.  This  should be  set to charge until  14.6V is reached, to hold this for a short period, typically an hour but it depends a bit  on the B2B and the Li battery size and make.  After that, the B2B goes to float at say 13.2 V.  This is less than battery voltage so the Li is not charged.  Once the Li voltage drops the B2B starts up again and the cycle repeats.  All the while though the alternator has been holding the start battery at 14.6 V, which is OK for a less acid.  Exact best voltages need to be looked up in the battery data sheets.

 

The solar MPPT should be set up in a similar fashion to the B2B.  Constant current to 14.6V,  hold for a short while, float at 13.4 V or less.

 

I think Moomin Papa has a successful single A127 based hybrid. No doubt he will be along.

 

N

[Tasemu]

6 minutes ago, Tony Brooks said:

Originally non-bi-directional VSRs were available, they may still be. However, I am not sure of the wisdom of charging a lithium in that way because of the need for a different charging profile and the need to shut the charging down to prevent damage.

 

Ah sorry forgot to saw we are running the lithiums through a BMS which has been configured for hybrid, so shouldn't run into those issues theoretically.

5 minutes ago, BEngo said:

Not all VSR's are dual sensing. If you find a single sense one, and connect it right the Li will be disconnected when the alternator shuts down.  It will not cure the problem of possible overcharging of the Li.

 

Single alternator with B2B is there to avoid floating the Li at excessive voltages and overcharging it.   

 

In a 12V set up. Once the Li is fully charged at about 3.64 V per cell and the voltage is the same across all the cells in the pack (top balanced)  you want to STOP charging entirely.   Holding the battery at 14.6v or more when full  causes it to carry on trying to charge and is  * bad*  for the Li.   So the B2B is brought in.  This  should be  set to charge until  14.6V is reached, to hold this for a short period, typically an hour but it depends a bit  on the B2B and the Li battery size and make.  After that, the B2B goes to float at say 13.2 V.  This is less than battery voltage so the Li is not charged.  Once the Li voltage drops the B2B starts up again and the cycle repeats.  All the while though the alternator has been holding the start battery at 14.6 V, which is OK for a less acid.  Exact best voltages need to be looked up in the battery data sheets.

 

The solar MPPT should be set up in a similar fashion to the B2B.  Constant current to 14.6V,  hold for a short while, float at 13.4 V or less.

 

I think Moomin Papa has a successful single A127 based hybrid. No doubt he will be along.

 

N

 

Thanks for the info, yeah we have all charge parameters set up and the BMS is set up to stop the engine overcharging or floating it at high voltage for too long.

Also the one we have does technically only sense on the starter side for activation, its the disconnection that is the issue it seems.

[BEngo]

What are you using to control the alternator charging parameters please?  

 

N

 

 

[Tasemu]

48 minutes ago, BEngo said:

What are you using to control the alternator charging parameters please?  

 

N

 

 

 

We're using a BMS to control what gets into the cells.

 

EDIT: Sorry if i'm misunderstanding and I do appreciate the help. The alternator is charging at ~14v but the BMS itself is what is cutting off the charge before it can do any harm. We don't have anything that is effecting the alternator itself. I've seen this setup before and am fairly sure there isn't anything wrong with it. Its just a standard hybrid LA/Lifepo4 setup. Though we just don't want to crank off the lithiums with this VSR connected as i've heard thats not a good thing to do with them.

 

EDIT 2: We have set the tolerances on the BMS quite low, so when the pack voltage hits 14.2v it disconnects from the system. This still gives it enough SoC to efficiently work on passively balancing the cells, and anything else can be trickled in by the solar over time.

Edited February 9, 2023 by Tasemu

[Tony1]

 

Apologies if I've misunderstood the issue, as I'm certainly no expert, but if I have got it right, your issue is that you don't want the lithium battery to pass any charge back to the lead acid battery. 

I have a roughly similar sort of thing. I have 2 lead acid batteries (one for each alternator). Eeach lead acid battery supplies charge to my lithium battery bank, via its own B2B charger. 

 

But I am concerned that the lead acid batteries are not being looked after very well in this setup, for a lot of the year. This is because In my case I have a lot of panels, so between March-Nov I hardly ever run the engine to do charging- the lithiums get everything from the panels.

I probably start the engine once a week to do a cruise, but sometimes its once every two weeks. So in general,  the lead acid batteries are not getting enough of a charge. 

When I do charge using the engine, it is done via B2Bs, which do not allow any charge back to the lead acid batteries. 

 

So in my case I have this issue where the lead acid batteries are not getting anything back from the lithiums, but I see it as a potential problem that will lead to the lead acids deteriorating. 

So I'm looking at possible ways of getting some charge back from the lithiums into the lead acids, or maybe a switch to divert the MPPT charge from the lithiums into the lead acids. 

 

 

 

[Tasemu]

14 minutes ago, Tony1 said:

 

Apologies if I've misunderstood the issue, as I'm certainly no expert, but if I have got it right, your issue is that you don't want the lithium battery to pass any charge back to the lead acid battery. 

I have a roughly similar sort of thing. I have 2 lead acid batteries (one for each alternator). Eeach lead acid battery supplies charge to my lithium battery bank, via its own B2B charger. 

 

But I am concerned that the lead acid batteries are not being looked after very well in this setup, for a lot of the year. This is because In my case I have a lot of panels, so between March-Nov I hardly ever run the engine to do charging- the lithiums get everything from the panels.

I probably start the engine once a week to do a cruise, but sometimes its once every two weeks. So in general,  the lead acid batteries are not getting enough of a charge. 

When I do charge using the engine, it is done via B2Bs, which do not allow any charge back to the lead acid batteries. 

 

So in my case I have this issue where the lead acid batteries are not getting anything back from the lithiums, but I see it as a potential problem that will lead to the lead acids deteriorating. 

So I'm looking at possible ways of getting some charge back from the lithiums into the lead acids, or maybe a switch to divert the MPPT charge from the lithiums into the lead acids. 

 

 

 

 

Sort of, all i'm really worried about is that the VSR is not disconnecting on engine shutdown, so the next time I start the engine it would be cranking off the lithium bank. And I've heard that's a no-no.

[Tony Brooks]

1 hour ago, Tasemu said:

 

Also the one we have does technically only sense on the starter side for activation, its the disconnection that is the issue it seems.

 

So it seems it is the solar charge to the engine bank that is keeping the VSR energised, if I understand what you are saying. So the question is how to prevent this happening. It seems to me that as engine batteries spend all the time all but fully charged and you are relying upon the BMS to do the lithium disconnect, you could connect the solar to the lithiums. That would make maximum use of the solar output, but when the alternator is charging the VSR would cut in and connect the two banks just as it does now. Engine stops, alternator output drops to zero, and the engine battery voltage could not hold the VSR engaged.

[Tasemu]

4 minutes ago, Tony Brooks said:

 

So it seems it is the solar charge to the engine bank that is keeping the VSR energised, if I understand what you are saying. So the question is how to prevent this happening. It seems to me that as engine batteries spend all the time all but fully charged and you are relying upon the BMS to do the lithium disconnect, you could connect the solar to the lithiums. That would make maximum use of the solar output, but when the alternator is charging the VSR would cut in and connect the two banks just as it does now. Engine stops, alternator output drops to zero, and the engine battery voltage could not hold the VSR engaged.

 

This is how we currently have it set up, the solar is connected to the lithiums. It appears that once the VSR engages it 'combines the batteries' which makes sense. This allows voltage of the Lifepo4 pack + the solar to be able to charge the starter too. Once the engine is stopped, because the VSR is engaged for a second or so and the batteries are still combined, this then allows the 'leisure side' of the VSR to feed power into the starter and never let it drop down below the VSR dis-engage voltage.

[Tony Brooks]

4 minutes ago, Tasemu said:

 

This is how we currently have it set up, the solar is connected to the lithiums. It appears that once the VSR engages it 'combines the batteries' which makes sense. This allows voltage of the Lifepo4 pack + the solar to be able to charge the starter too. Once the engine is stopped, because the VSR is engaged for a second or so and the batteries are still combined, this then allows the 'leisure side' of the VSR to feed power into the starter and never let it drop down below the VSR dis-engage voltage.

 

I wonder if it is a faulty VSR. It still seems it is the solar voltage unless you have the lithium charging voltage at 14.6 or more (typical VSR cut out voltage). What happens if you turn the solar off and try again.

 

I fear it may be pointing to the need for a BtoB.

Edited February 9, 2023 by Tony Brooks

[Tony1]

7 minutes ago, Tasemu said:

 

Sort of, all i'm really worried about is that the VSR is not disconnecting on engine shutdown, so the next time I start the engine it would be cranking off the lithium bank. And I've heard that's a no-no.

 

Yes of course- I'm sure you're right. I didnt know this, but it seems like starter motors can draw 400 amps or more, which is more than I would ever want to pull from my 400Ah lithium battery bank.

I get worried when I draw 80 amps or so for the immersion heater, it feels like I'm stressing them more than is ideal if I want to get maximum life from them.  

 

 

[Tasemu]

28 minutes ago, Tony Brooks said:

 

I wonder if it is a faulty VSR. It still seems it is the solar voltage unless you have the lithium charging voltage at 14.6 or more (typical VSR cut out voltage). What happens if you turn the solar off and try again.

 

I fear it may be pointing to the need for a BtoB.

 

The VSR cuts-in at 13.3v and wont cut-out until the voltage drops to 12.8.

[nicknorman]

22 minutes ago, Tasemu said:

 

The VSR cuts-in at 13.3v and wont cut-out until the voltage drops to 12.8.

Bearing in mind that when the VSR is on, the voltage on the Li and the starter batteries will by definition be (more or less) identical. And the Li will sit well over 12.8v even well quite well discharged. So the strategy isn’t going to work, as you have discovered!

What you want is for the batteries to be connected together when the engine is running, and disconnected when not. A good engine running indicator is the alternator D+ terminal (assuming it has a 9 diode alternator). So one solution would be a motorised battery switch that is turned on by the presence of 12v on the D+ terminal, and turned off when that voltage drops to near zero. Or of course a manual battery switch, but that is prone to human error.

 

I know you aren’t asking about protection of the Li during charging using the BMS, but I will mention that the devil is in the detail. What you want is for the batteries to be charged until the voltage reaches some limit, say 14 to 14.2v (max 14.6v if you are sure they are perfectly top balanced) and the current has dropped to about 5% of capacity, then charging to stop, and not restart until there has been significant discharge. Presumably your BMS has separate connections for charge and discharge?

What you want to avoid is charging stopping when voltage hit say 14.4v and then restarting when it drops to say 13.8v. With that, you will be repeatedly ramming the maximum amount of charge into the batteries, which isn’t good for longevity.

 

But I also suggest that the Sterling B2Bs are pretty horrid things, very expensive and very inefficient.

 

Edited February 9, 2023 by nicknorman

[Tony Brooks]

46 minutes ago, Tasemu said:

 

The VSR cuts-in at 13.3v and wont cut-out until the voltage drops to 12.8.

 

I stand corrected, thanks. I am sure my bog-standard VSR cut in at about 13.6 and out at about 13.3 but as the boat is sold I can't check it.

 

[Adam]

Use a standard "dumb" 200a relay using the charge light as the switch (so comes on when the engine is running and switches off when the engine is)

[TheBiscuits]

14 hours ago, nicknorman said:

I also suggest that the Sterling B2Bs are pretty horrid things, very expensive and very inefficient.

 

Wonderful space heaters though if you install them so they blow on your feet when steering....

 

 

[Tony Brooks]

11 hours ago, Adam said:

Use a standard "dumb" 200a relay using the charge light as the switch (so comes on when the engine is running and switches off when the engine is)

 

There is a potential problem with this that means care in selecting the relay is important. I found that some relays would close with the current from the warning lamp, so if the OP had one of these it may still allow the starter to draw current from the lithium bank and the relay contact may be short-lived. The other thing to consider is that the relay coil will "rob" some warning lamp current, making alternator energisation somewhat reluctant. Improving the energisation by fitting a higher wattage warning lamp or a parallel resistor makes it more likely that the relay contacts will close as soon as the ignition is turned on. I think there may be a degree of suck it and see needed.

[Tracy D'arth]

Use the oil pressure switch to switch the negative of the relay.

 

 

Edited February 10, 2023 by Tracy D'arth

[1st ade]

2 minutes ago, Tracy D'arth said:

Use the oil pressure switch to switch the negative of the relay.

Just what I was about to suggest!

[Tracy D'arth]

Oh, what great minds do so think alike!

[Tony Brooks]

4 minutes ago, Tracy D'arth said:

Use the oil pressure switch to switch the negative of the relay.

 

That won't work because it is closed with no oil pressure, otherwise the lamp would not come on when oil pressure failed, but a rising oil pressure switch (if they are still available) would be ideal. One of those could control the relay directly with no effect on alternator energisation.

Edited February 10, 2023 by Tony Brooks

[rusty69]

9 minutes ago, Tracy D'arth said:

looked again at the capacitor and diode arrangement. With the inductance of the relay in the cold start control box it is indeed a relaxation oscillator and is responsible for the flashing of the lights. You could prove it by disconnecting one end.

Is this comment on the correct thread? 

[Tracy D'arth]

9 minutes ago, rusty69 said:

Is this comment on the correct thread? 

Of course not, I'm old and addled. Well spotted. That is the problem with edits, they go where they want.

Thanks.

[rusty69]

1 minute ago, Tracy D'arth said:

Of course not, I'm old and addled. Well spotted. That is the problem with edits, they go where they want.

Thanks.

S'ok.I thought it a good comment that may help the guy with the flashing light problem.