Split relay troubles

[Ewan123]

I recently installed a split charge relay (replacing a split charge diode), with thanks to @Tony Brooks for http://www.tb-training.co.uk/MarineE09.html 👍 in order to get the port alternator to join the leisure charging as that's a hybrid lithium bank so can take much more than the 50Aish it's currently getting from just the starboard alternator.

 

However, it hasn't been connecting the battery banks when the engine is running. The port alternator is only charging the starter and bowthruster bank, the starboard alternator is only charging the leisure bank (I can tell as each alternator matches the voltage of each bank and there's a difference between the two, and I'm only getting 50Aish into the Leisure which seems right for one 70A, not two together).

 

I think I may have identified a possible cause, but I don't know what to do about it (if indeed it is the cause). I've got the relay energising wire going to the warning lamp (circled blue in the image below, marked "W" on the alternator case. This measures 0V with the engine off, and only half the charging voltage with the engine on, e.g. charging at 14.2V, this connection shows 7.1V (measured with the alternator case as the -ve). I can't find another connection on the alternator that is 0V engine off and charging voltage with engine on.

 

 

Should this connection not be getting up to the same as the charging voltage?

Could this be the reason for the relay not connecting the battery banks?

[Canal321]

Hi I'm no expert but I have wired a few alternators. 

I think the W terminal is for the tacho, you need to connect the split charge to the d+ terminal. If I'm seeing it correct that should be the brown wire with the yellow stripe. 

 But like I say I'm not expert, maybe wait for Tony to answer. 

[Tony Brooks]

11 minutes ago, Canal321 said:

Hi I'm no expert but I have wired a few alternators. 

I think the W terminal is for the tacho, you need to connect the split charge to the d+ terminal. If I'm seeing it correct that should be the brown wire with the yellow stripe. 

 But like I say I'm not expert, maybe wait for Tony to answer. 

No need, you have it.

 

The thin brown wire with a 6mm female blade on the end and gong into a roughly rectangular shaped hole in the back of the alternator is the D+

 

It might be easier to run a cable from the charge warning lamp terminal, the one on the alternator side of the bulb.

I am not too sure about the readily available split charge relays being able to cope with the long term current flows lithium batteries produce.

[Ewan123]

Well I'm not too surprised that I failed to follow the wires properly to identify the connections 🤦‍♂️ thank you both.

 

59 minutes ago, Tony Brooks said:

I am not too sure about the readily available split charge relays being able to cope with the long term current flows lithium batteries produce.

 

I don't expect to be getting much more than 100A out of the two alternators, so hoped the 200A relay should do well enough.

[Tony Brooks]

Just now, Ewan123 said:

Well I'm not too surprised that I failed to follow the wires properly to identify the connections 🤦‍♂️ thank you both.

 

 

I don't expect to be getting much more than 100A out of the two alternators, so hoped the 200A relay should do well enough.

 

Let's hope so, I don't trust the maximum current rating on a lot of the stuff that seems to originate in the Far East, not that I have any proof a [articular item may have optimistic specs.

[Ewan123]

I did splash out on a genuine Durite part with similar thoughts, didn't fancy risking a cheapo.

[Ewan123]

On 02/09/2024 at 19:13, Tony Brooks said:

It might be easier to run a cable from the charge warning lamp terminal, the one on the alternator side of the bulb.

I did something which I thought was what you suggested here but I may have got confused... I've joined the relay cable to the cable running to/from the alternator warning light bulb - does that sound/look right?? It doesn't appear to have resolved the issue though so I'm guessing not.

 

(Sticking them both into the wago connection was just a quick method to test)

[Tony Brooks]

10 minutes ago, Ewan123 said:

I did something which I thought was what you suggested here but I may have got confused... I've joined the relay cable to the cable running to/from the alternator warning light bulb - does that sound/look right?? It doesn't appear to have resolved the issue though so I'm guessing not.

 

(Sticking them both into the wago connection was just a quick method to test)

 

I can't work out what I am looking at. I can't see the bulb holder for what I assume is the charge lamp, and there seems to be too many wires. What is the black disk with the silver nut around it.

 

Where is the relay coil negative cable? I think there is a shadow of the black wire in the photo.

 

I don't think that is the charge light bulb. If it were, there should only be one wire on the alternator side until you add the relay coil positive. It might be just an ignition on warning lamp.

 

I suspect the white wire comes from the ignition switch, which is why it is connected to another lamp. That means the red cable is the ign. on feed to the charge light. The black wire on the bulb should go straight to D+ on the alternator, with no other connections to it, but it s T'd into the green cable that also seems to feed another warning lamp.

 

Assuming the feed from the ignition switch is looped into each warning lamp, then whichever wire that is should be a single wire feeding the bulb. The other bulb terminal should run to D+ with the new relay wire attached. I would comment that the 1.5w bulb you seem to have may not be large enough to supply the relay couil AND energise the alternator.

[jonathanA]

I can't help think it's easier to run a wire to split charge relay coil direct from the d+ terminal in the alternator. Presumably the relay is close to the engine and batteries. I think the D+ was previously identified as the brown/yellow on the alt. Would save all the confusion about what wire is what at the panel for the op. 

[Ewan123]

57 minutes ago, Tony Brooks said:

 

I can't work out what I am looking at. I can't see the bulb holder for what I assume is the charge lamp, and there seems to be too many wires. What is the black disk with the silver nut around it.

 

Where is the relay coil negative cable? I think there is a shadow of the black wire in the photo.

 

I don't think that is the charge light bulb. If it were, there should only be one wire on the alternator side until you add the relay coil positive. It might be just an ignition on warning lamp.

 

I suspect the white wire comes from the ignition switch, which is why it is connected to another lamp. That means the red cable is the ign. on feed to the charge light. The black wire on the bulb should go straight to D+ on the alternator, with no other connections to it, but it s T'd into the green cable that also seems to feed another warning lamp.

 

Assuming the feed from the ignition switch is looped into each warning lamp, then whichever wire that is should be a single wire feeding the bulb. The other bulb terminal should run to D+ with the new relay wire attached. I would comment that the 1.5w bulb you seem to have may not be large enough to supply the relay couil AND energise the alternator.

I'll explain what we're looking at there as best I can: there are two bulbs, one visible in the image (dark green and black wire attached, which I put the relay cable onto with the wago) and one we can only see the back of (white and green wires attached) which is in the engine control panel. I'm not sure what the purpose of the one we can see is as it just hangs around in a closed cupboard. Both bulbs illuminate with ignition (along with the buzzer sounding) and go off shortly after ignition.

 

There's just the one -ve cable from the relay here going into that wago connector. The other -ve from the relay goes straight to the battery negative post.

 

19 minutes ago, jonathanA said:

I can't help think it's easier to run a wire to split charge relay coil direct from the d+ terminal in the alternator. Presumably the relay is close to the engine and batteries. I think the D+ was previously identified as the brown/yellow on the alt. Would save all the confusion about what wire is what at the panel for the op. 

 

I think that may well be easier, I just didn't have any appropriate connections to do it with at this moment. I'll get a proper spade splitter to go straight into the D+ on the alternator.

[Tony Brooks]

I now think that there are two bulbs in parallel, presumably to help exite the alternator so if the white wire is ign. on pos. then the relay coil positive is on the wrong side of the bulb, BUT that should have made it energise as soon as the ignition is turned on. If I am correct, then it looks as if the green wire changes to brown & yellow somewhere along the harness.

 

There should be thin positive and a negative wires on the relay or two small 6mm blades, depending upon the relay. Both wires might be black, but that does not mean both are negatives.

 

If you are putting two terminal on the D+ in the alternator ensure there is no way the terminals can move and short out on the case, the hole in the case is not very large.

 

I think that you need to find out which cable (white or green) is the ign. on pos.

[Ewan123]

11 hours ago, Tony Brooks said:

I now think that there are two bulbs in parallel, presumably to help exite the alternator so if the white wire is ign. on pos. then the relay coil positive is on the wrong side of the bulb, BUT that should have made it energise as soon as the ignition is turned on. If I am correct, then it looks as if the green wire changes to brown & yellow somewhere along the harness.

 

There should be thin positive and a negative wires on the relay or two small 6mm blades, depending upon the relay. Both wires might be black, but that does not mean both are negatives.

 

If you are putting two terminal on the D+ in the alternator ensure there is no way the terminals can move and short out on the case, the hole in the case is not very large.

 

I think that you need to find out which cable (white or green) is the ign. on pos.

I've just checked with the multimeter and the white cable is positive with ignition on (though across each bulb I only measure about 8.5V?). I tried swapping the relay cable to the other side of the visible bulb but no difference - in theory would I want to connect the relay cable to the green negative cable before it splits off between the two bulbs, so it's getting the full power? (This is more for my education at this point, I've ordered a piggyback spade connector for the D+ and will be careful of shorting, thanks).

[jonathanA]

I assume that was with the engine off, but ignition on ? Once running there should be zero or very little voltage across the bulb 

, so the bulb is not glowing. 

 

I'm not sure what type of piggy back you have ordered but I would think there may not be enough space for one. Anyway as Tony points out be careful. Might be worth making up a short female to male lead to fit between the alt terminal and your piggy back. 

[Tony Brooks]

1 hour ago, Ewan123 said:

I've just checked with the multimeter and the white cable is positive with ignition on (though across each bulb I only measure about 8.5V?). I tried swapping the relay cable to the other side of the visible bulb but no difference - in theory would I want to connect the relay cable to the green negative cable before it splits off between the two bulbs, so it's getting the full power? (This is more for my education at this point, I've ordered a piggyback spade connector for the D+ and will be careful of shorting, thanks).

 

Taking this at face value. As wired in the photo as long as the negative relay connection is a good negative then the relay should have clicked in at the moment you turned the ignition on, it seems it did not, so that means either there is a poor connection in one of the connectors or a negative problem.

 

Personally, I would look at the bulb in the black warning lamp and if 2 watts or above, simply take the extra bulb out of circuit and see how the alternator energises. If it does, be it with a slight rev on starting, then I would reconnect the relay to the green wire.

 

Measuring between the green wire and a decent negative should give you more or less charging voltage with the engine running and the warning lamp out. If it does, then connecting the relay to the green wire should make the relay work - assuming a good relay negative connection. if it does not, then it looks like a faulty relay. Try connecting the two thin wires across a battery and see if it clicks each time you make contact, OR measure the resistance/continuity between the two thin wires. Any mis-wiring you may have done can not have damaged the relay coil circuit, even if it had a surge quench diode and you reverse connected it so the diode blew. The relay would still work.

 

Edited September 5 by Tony Brooks

[Eeyore]

@Tony Brooks saved me a lot of typing 😎

Its possible the relay coil could be damaged by connection to what is effectively a low voltage ac supply? Probably going to heat the coil fairly quickly, the resistance check will confirm.

 

[Tony Brooks]

1 minute ago, Eeyore said:

@Tony Brooks saved me a lot of typing 😎

Its possible the relay coil could be damaged by connection to what is effectively a low voltage ac supply? Probably going to heat the coil fairly quickly, the resistance check will confirm.

 

FWIW, for reasons I won't go into, I ran my split charge relay from the W terminal on the Paris-Rhone alternator with no bad consequences. I was more concerned about a single unbalanced phase, but it was OK. In any case, the W terminal provides a pulsed DC supply because a negative diode is still in circuit doing half-wave rectification. I feared that may allow the relay contacts to "chatter" and burn, but apparently not.

[Ewan123]

2 hours ago, Tony Brooks said:

 

Taking this at face value. As wired in the photo as long as the negative relay connection is a good negative then the relay should have clicked in at the moment you turned the ignition on, it seems it did not, so that means either there is a poor connection in one of the connectors or a negative problem.

 

Personally, I would look at the bulb in the black warning lamp and if 2 watts or above, simply take the extra bulb out of circuit and see how the alternator energises. If it does, be it with a slight rev on starting, then I would reconnect the relay to the green wire.

 

Measuring between the green wire and a decent negative should give you more or less charging voltage with the engine running and the warning lamp out. If it does, then connecting the relay to the green wire should make the relay work - assuming a good relay negative connection. if it does not, then it looks like a faulty relay. Try connecting the two thin wires across a battery and see if it clicks each time you make contact, OR measure the resistance/continuity between the two thin wires. Any mis-wiring you may have done can not have damaged the relay coil circuit, even if it had a surge quench diode and you reverse connected it so the diode blew. The relay would still work.

 

I've tested the relay with wires across a battery, it clicks nicely. I did this with the engine running too - nice click, no change in charge behaviour. So that narrows it down to the other two connections on the relay! The port/starter alternator is definitely correctly connected to the relay 👍but the connection to the leisure battery positive... I used a cable that was connected to the diode splitter which I think should have been right, but it's a sod to follow - seems to go through the inverter-charger (and at the very least takes a much more circuitous route than apparently necessary for the relay). I think this might be the only remaining possible issue. Spare time is running out now and I might not have a cable spare to easily rectify that connection, but I'll report back in a few days hopefully. 

[Tony Brooks]

35 minutes ago, Ewan123 said:

I've tested the relay with wires across a battery, it clicks nicely. I did this with the engine running too - nice click, no change in charge behaviour. So that narrows it down to the other two connections on the relay! The port/starter alternator is definitely correctly connected to the relay 👍but the connection to the leisure battery positive... I used a cable that was connected to the diode splitter which I think should have been right, but it's a sod to follow - seems to go through the inverter-charger (and at the very least takes a much more circuitous route than apparently necessary for the relay). I think this might be the only remaining possible issue. Spare time is running out now and I might not have a cable spare to easily rectify that connection, but I'll report back in a few days hopefully. 

 

I think that you may be overcomplicating things. My website does NOT deal with split charge relays when used with mixed LA and lithium banks, it only deals with split charging for toe LA banks.

 

Having gone back to the start of this thread, I think that you may be in danger of destroying the lithium bank or an alternator. As I understand things, you simply can't have automotive alternators charging lithium batteries unless you also fit an expensive alternator controller that will provide a greater control of charging voltage AND maximum currant than the automotive alternator can provide. Without such control, you need to let the automotive alternatorS charge the engine battery and then use the engine battery to charge the lithium bank. The bodge way (that may shortly be forbidden) is a long piece f cable connecting the two to limit the charging voltage at the lithium bank or a battery to battery charger that can be programmed to limit current and maximum voltage.

Because this needs to appear to the alternators as a singe battery bank set up, considerable rewiring is required. However, the lithium domestic bank is fed, be it a long piece of wire or a B2B, both alternators need to feed the LA engine battery, otherwise the one on the lithium battery will cause you grief of one sort or another.

 

I am happy for those with more knowledge of lithium systems to correct me if needed.

 

I don't think that you need a relay unless it is a long wire system and the relay disconnects the long wire when no charging is taking place. A B2B should do that automatically.

 

Assuming either system is in use.

 

I would just connect the original domestic alternator to a suitable point on the engine battery circuit. For full BSS compliance, that would be on the load side of the engine master switch.

 

At a high state of engine battery charge, one alternator might shut down, but I doubt it will as long as the lithium bank is drawing maximum current. After that, one alternator will be delivering as much charge as the LA battery is willing to take.

 

 

Edited September 5 by Tony Brooks

[Ewan123]

23 hours ago, Tony Brooks said:

I think that you may be overcomplicating things.

 

Given that the relay works and I can get the small wires to the right places now (thanks for all of the advice to get me that far), it seems like it can only be an incorrect connection to the batteries now though, does it not?

 

On 05/09/2024 at 15:10, Tony Brooks said:

My website does NOT deal with split charge relays when used with mixed LA and lithium banks, it only deals with split charging for toe LA banks.

 

Having gone back to the start of this thread, I think that you may be in danger of destroying the lithium bank or an alternator. As I understand things, you simply can't have automotive alternators charging lithium batteries unless you also fit an expensive alternator controller that will provide a greater control of charging voltage AND maximum currant than the automotive alternator can provide. Without such control, you need to let the automotive alternatorS charge the engine battery and then use the engine battery to charge the lithium bank. The bodge way (that may shortly be forbidden) is a long piece f cable connecting the two to limit the charging voltage at the lithium bank or a battery to battery charger that can be programmed to limit current and maximum voltage.

Because this needs to appear to the alternators as a singe battery bank set up, considerable rewiring is required. However, the lithium domestic bank is fed, be it a long piece of wire or a B2B, both alternators need to feed the LA engine battery, otherwise the one on the lithium battery will cause you grief of one sort or another.

 

I am happy for those with more knowledge of lithium systems to correct me if needed.

 

I don't think that you need a relay unless it is a long wire system and the relay disconnects the long wire when no charging is taking place. A B2B should do that automatically.

 

Assuming either system is in use.

 

I'm happy to be corrected, but I'm not sure there's much difference between a split charge relay working with two LA banks vs one LA and one hybrid LA/lithium. The hybrid bank will draw more power for longer, so care needs to be taken with the alternator, but otherwise no difference?

 

I understand the potential issues with the lithiums working an alternator too hard - I'll be monitoring the Amps from each alternator as well as the temperature of the alternators to ensure they're not getting overworked by the lithium. As it stands, (no B2B, I've not installed any long wire system as there seemed to be enough resistance in the system already, such that it wasn't necessary for the domestic alternator) the domestic alternator is charging the lithium hybrid bank without problems - the alternator (rated 70A) remains below 80°C and puts out no more than about 50A at the most, so I believe that's within the capabilities of the alternator (all I changed in the charging system when adding the lithium was disconnecting an external Sterling regulator from that alternator). I'll monitor the same on the engine alternator once I get the relay working and make some changes if the alternator gets worked too hard - I'm aware that since it already gets to a good charging voltage without an external regulator upping the voltage, I might need to keep a closer eye on this one to be sure the lithium doesn't make it work too hard.

 

On 05/09/2024 at 15:10, Tony Brooks said:

I would just connect the original domestic alternator to a suitable point on the engine battery circuit. For full BSS compliance, that would be on the load side of the engine master switch.

 

At a high state of engine battery charge, one alternator might shut down, but I doubt it will as long as the lithium bank is drawing maximum current. After that, one alternator will be delivering as much charge as the LA battery is willing to take.

 

So... two alternators charging the engine battery, and the relay connecting the engine bank and domestic bank when the engine is running? I'm not sure I understand the significance of this different approach.

 

Thanks for your continued patience and assistance.

[Tony Brooks]

46 minutes ago, Ewan123 said:

 

Given that the relay works and I can get the small wires to the right places now (thanks for all of the advice to get me that far), it seems like it can only be an incorrect connection to the batteries now though, does it not?

 

 

I'm happy to be corrected, but I'm not sure there's much difference between a split charge relay working with two LA banks vs one LA and one hybrid LA/lithium. The hybrid bank will draw more power for longer, so care needs to be taken with the alternator, but otherwise no difference?

 

I understand the potential issues with the lithiums working an alternator too hard - I'll be monitoring the Amps from each alternator as well as the temperature of the alternators to ensure they're not getting overworked by the lithium. As it stands, (no B2B, I've not installed any long wire system as there seemed to be enough resistance in the system already, such that it wasn't necessary for the domestic alternator) the domestic alternator is charging the lithium hybrid bank without problems - the alternator (rated 70A) remains below 80°C and puts out no more than about 50A at the most, so I believe that's within the capabilities of the alternator (all I changed in the charging system when adding the lithium was disconnecting an external Sterling regulator from that alternator). I'll monitor the same on the engine alternator once I get the relay working and make some changes if the alternator gets worked too hard - I'm aware that since it already gets to a good charging voltage without an external regulator upping the voltage, I might need to keep a closer eye on this one to be sure the lithium doesn't make it work too hard.

 

 

So... two alternators charging the engine battery, and the relay connecting the engine bank and domestic bank when the engine is running? I'm not sure I understand the significance of this different approach.

 

Thanks for your continued patience and assistance.

 

As I understand things lithium:

 

With an automotive alternator and no LA "buffer" when the lithium control system or BMS simply open circuits the charging to prevent overcharging and killing the lithiums it will cause a voltage surge that can and does wreck the electronics in the alternator. There are surge suppression components in the alternator, but they can not be relied upon to be 100% effective, so with lithiums one would expect the control system or the BMS to disconnect the alternator regularly giving a greater chance of alternator damage.

 

It is perfectly safe to control the charging of lead acid batteries by the crude automotive regulators simply referencing the charging voltage, but they are too crude to prevent damage to lithium cells. On LA batteries, the voltage gradually rises as they charge, so providing they are set to just below the batteries gassing voltage, no damage will occur. On lithiums the voltage does not rise in the same way. It stays high until the cells are virtually fully charged and then drops of a bit. This is called the knee, but if you regularly take the batteries up to the knee voltage and especially if you keep charging, the lithium cells will be damaged. The standard automotive regulator is too crude for the safe charging of lithium batteries.

 

There is no doubt that because the voltage does not rise in the same way with lithium cells and the internal resistance of the battery is so low the alternator with the automotive regulator will charge at its maximum output and that will lead to it running hot and possible damage. So ideally a way has to be found to stop this happening. Now A127 alternators started life with a 50 amp output, but nowadays they are often rated as high as 75 amps, so I am not sure why you only get 50 amps and why it does not run far hotter than 80C. The fact you had a Sterling controller suggests that there may be a resistance problem in the wiring that the Sterling device covered up. I also wonder if the alternator may already have some open circuit diodes that reduce its maximum charging voltage and maximum output.

 

The difference between using automotive alternators to charge LA and lithium banks are described above, the voltage regulation is not really suitable AND there is no current control, the alternators rely upon the fact that LA batteries only accept the currant they want, lithiums will take it all plus more if they get a chance, until the cells are damaged.

 

The above is as I understand things and would welcome the input from @nicknorman and any others who have been using lithiums for a long time. Note that Nick who is very knowledgable in electronics felt it necessary to build his own alternator regulator to suit his lithium bank, because here was nothing on the market that was suitable at the time. The control needs far more accuracy and sophistication than an automotive regulator can provide.

 

I am not clear why a two alternator engine ever needed a split charge diode unless it was also charging another bank like a bow thruster. The diode system would explain why the Sterling was fitted and if it was still in use the roughly 0.7V volt drop through the diodes may have been enough to protect the alternator.

 

Assuming diode had an alternator charge cable fitted (B+) and a charging cable to the domestic and another to the engine battery (but why that should be I don't know) I also don't know how the engine alternator is wired.

 

I think that you want to keep one alternator connected to the lithium bank (until the BMS disconnects it), and the other permanently connected to the engine battery, but combine the two to both banks when the engine is running. If so the wiring needs modifying in this sort of way.

 

By all means join the alternator B+ cable at the diode to the one that feeds the relevant battery bank. Then the other alternator B+ needs connecting to its bank. This might mean running an extra cable.

 

Now you have each alternator charging its own bank.

 

To combine the charges, connect one of the split charge relay large terminals to one battery bank positive and the other relay terminal to the other bank positive.

 

Connect one thin relay wire to battery negative, ensuring both bank's negatives are linked as is standard. you seem to have already connected this cable.

 

Connect the other thin relay wire to D+ on whichever alternator you want to control it.

 

That should work, but I take no responsibility if you suffer damage.

 

I also get a feeling there is more to this than you let on, like why the split charge diode on a twin alternator engine, so without an accurate circuit diagram I don't really know what is going on.

 

 

1 hour ago, Ewan123 said:

So... two alternators charging the engine battery, and the relay connecting the engine bank and domestic bank when the engine is running? I'm not sure I understand the significance of this different approach.

 

The significance is that it provides a LA buffer battery for when the lithium BMS shuts the charging down in a very crude way.

 

It also removes a potential point of failure (the relay contacts) from a circuit that is likely to carry high currents for long periods.

 

This is only appropriate if you are using the LA battery as a buffer against alternator shut down damage, and it seems that you are not.

 

 

 

 

[Ewan123]

On 06/09/2024 at 17:05, Tony Brooks said:

 

As I understand things lithium:

 

With an automotive alternator and no LA "buffer" when the lithium control system or BMS simply open circuits the charging to prevent overcharging and killing the lithiums it will cause a voltage surge that can and does wreck the electronics in the alternator. There are surge suppression components in the alternator, but they can not be relied upon to be 100% effective, so with lithiums one would expect the control system or the BMS to disconnect the alternator regularly giving a greater chance of alternator damage.

 

It is perfectly safe to control the charging of lead acid batteries by the crude automotive regulators simply referencing the charging voltage, but they are too crude to prevent damage to lithium cells. On LA batteries, the voltage gradually rises as they charge, so providing they are set to just below the batteries gassing voltage, no damage will occur. On lithiums the voltage does not rise in the same way. It stays high until the cells are virtually fully charged and then drops of a bit. This is called the knee, but if you regularly take the batteries up to the knee voltage and especially if you keep charging, the lithium cells will be damaged. The standard automotive regulator is too crude for the safe charging of lithium batteries.

 

There is no doubt that because the voltage does not rise in the same way with lithium cells and the internal resistance of the battery is so low the alternator with the automotive regulator will charge at its maximum output and that will lead to it running hot and possible damage. So ideally a way has to be found to stop this happening. Now A127 alternators started life with a 50 amp output, but nowadays they are often rated as high as 75 amps, so I am not sure why you only get 50 amps and why it does not run far hotter than 80C. The fact you had a Sterling controller suggests that there may be a resistance problem in the wiring that the Sterling device covered up. I also wonder if the alternator may already have some open circuit diodes that reduce its maximum charging voltage and maximum output.

 

The difference between using automotive alternators to charge LA and lithium banks are described above, the voltage regulation is not really suitable AND there is no current control, the alternators rely upon the fact that LA batteries only accept the currant they want, lithiums will take it all plus more if they get a chance, until the cells are damaged.

 

The above is as I understand things and would welcome the input from @nicknorman and any others who have been using lithiums for a long time. Note that Nick who is very knowledgable in electronics felt it necessary to build his own alternator regulator to suit his lithium bank, because here was nothing on the market that was suitable at the time. The control needs far more accuracy and sophistication than an automotive regulator can provide.

 

I am not clear why a two alternator engine ever needed a split charge diode unless it was also charging another bank like a bow thruster. The diode system would explain why the Sterling was fitted and if it was still in use the roughly 0.7V volt drop through the diodes may have been enough to protect the alternator.

 

Assuming diode had an alternator charge cable fitted (B+) and a charging cable to the domestic and another to the engine battery (but why that should be I don't know) I also don't know how the engine alternator is wired.

 

I think that you want to keep one alternator connected to the lithium bank (until the BMS disconnects it), and the other permanently connected to the engine battery, but combine the two to both banks when the engine is running. If so the wiring needs modifying in this sort of way.

 

By all means join the alternator B+ cable at the diode to the one that feeds the relevant battery bank. Then the other alternator B+ needs connecting to its bank. This might mean running an extra cable.

 

Now you have each alternator charging its own bank.

 

To combine the charges, connect one of the split charge relay large terminals to one battery bank positive and the other relay terminal to the other bank positive.

 

Connect one thin relay wire to battery negative, ensuring both bank's negatives are linked as is standard. you seem to have already connected this cable.

 

Connect the other thin relay wire to D+ on whichever alternator you want to control it.

 

That should work, but I take no responsibility if you suffer damage.

 

I also get a feeling there is more to this than you let on, like why the split charge diode on a twin alternator engine, so without an accurate circuit diagram I don't really know what is going on.

 

 

 

The significance is that it provides a LA buffer battery for when the lithium BMS shuts the charging down in a very crude way.

 

It also removes a potential point of failure (the relay contacts) from a circuit that is likely to carry high currents for long periods.

 

This is only appropriate if you are using the LA battery as a buffer against alternator shut down damage, and it seems that you are not.

 

 

 

 

I might have been unclear in the first place, apologies - the leisure bank comprises two Lithium and one LA in parallel, so we've got that LA buffer to protect the alternator when the Lithiums disconnect during charging.

 

Oh we do have a bow thruster battery as well... I had thought this was in parallel with the engine battery but now that I think about it, I'm not sure why I thought that. Time to follow some wires again I think - I guess the split charge diode was probably wired to that, and is what I've wired the relay to as a result. Which would explain why the relay appeared to click nicely but not affect the leisure bank charging. 

 

Assuming that's the case, is it a daft idea to parallel the starter and bow thruster batteries (the latter is ~58ft away in the bow) in order to have just two banks that the relay can connect?

[nicknorman]

41 minutes ago, Ewan123 said:

Assuming that's the case, is it a daft idea to parallel the starter and bow thruster batteries (the latter is ~58ft away in the bow) in order to have just two banks that the relay can connect?

 

Do you mean connect them directly, not via some sort of split charge device? I would not recommend it due to the possibility of the BT draining the starter battery and thus creating cold starting difficulties. In practice it will be OK most of the time, but one should design for worst case!

[Tony Brooks]

Just now, Ewan123 said:

I might have been unclear in the first place, apologies - the leisure bank comprises two Lithium and one LA in parallel, so we've got that LA buffer to protect the alternator when the Lithiums disconnect during charging.

 

Oh we do have a bow thruster battery as well... I had thought this was in parallel with the engine battery but now that I think about it, I'm not sure why I thought that. Time to follow some wires again I think - I guess the split charge diode was probably wired to that, and is what I've wired the relay to as a result. Which would explain why the relay appeared to click nicely but not affect the leisure bank charging. 

 

Assuming that's the case, is it a daft idea to parallel the starter and bow thruster batteries (the latter is ~58ft away in the bow) in order to have just two banks that the relay can connect?

 

Sorry, I have done my best to help, but with a lithium and LA battery paralleled with nothing between them to modify optimise the charging voltages I am bowing out. I very much fear that such a system may very shortly fall foul of new regulations, give insurance companies a "get out of jail free" card, and damage one or both battery types. None of this is certain, but whispers seem to indicate it is the way things are going.

[Ewan123]

50 minutes ago, Tony Brooks said:

 

Sorry, I have done my best to help, but with a lithium and LA battery paralleled with nothing between them to modify optimise the charging voltages I am bowing out. I very much fear that such a system may very shortly fall foul of new regulations, give insurance companies a "get out of jail free" card, and damage one or both battery types. None of this is certain, but whispers seem to indicate it is the way things are going.

Understood, thanks for your time.

6 hours ago, nicknorman said:

 

Do you mean connect them directly, not via some sort of split charge device? I would not recommend it due to the possibility of the BT draining the starter battery and thus creating cold starting difficulties. In practice it will be OK most of the time, but one should design for worst case!

Yes I thought that's why it wouldn't be ideal, thanks for confirming.