Split charging sanity check

[PCSB]

Hope everyone had as good a Christmas as possible. After a bit of a sanity check if possible 🤪

 

The current (no pun intended) situation is our bow thruster battery is charged via a split charge diode device from Sterling. The battery is not in great shape as it cannot supply power for very long - 10 or 15 seconds type thing. It soon flattens. Not sure if it is recoverable or not, will worry about that later. I won't replace it until I have sorted out the charging though.

 

I know that split charge diodes drop the voltage, the max I have seen at the battery end is 13.9v but when I measured that there were zero amps being drawn so indicating the battery was fully charged. After using the thruster the volatge dropped on the charging circuit to 13.1v. What was interesting was that the amperage when in use shot up to 69amps - this was on the charging cable NOT on the battery to thruster supply cable. This seems far too high to me for 110 Ah battery. I guess the split charge diode is a dumb device or the battery is goosed (or both). When not in use the amperage was around 17 or so briefly but seemed to drop off which I suspect is normal. 

 

My meter cannot read the draw from the battery to thruster as it exceeds the range.

 

I haven't yet checked the voltage from the alternator directly recently, the display in the engine control panel shows 14.5v. Next time I'm in the engine bay I'll do a quick check to confirm. The starter battery seems to be fine showing no signs of lacking power, even on the coldest days.

 

I intend to replace the split charge diode in the next month or two, I rarely use the bow thruster but its nice to have it as it can make life easier. I'm thinking of putting in something like the Victron Orion Smart DC-DC 12v 30A charger or Victron Argofet Battery Isolator. The latter would be the quicker switch as in wiring terms it looks to be a straight replacement but the Orion seems more controllable.

 

I'd like to stick with Victron kit if going the smart route as it makes life easier for me, inverter, shunt, mppt all being Victron therefore all available in one app.

 

So for the sanity check:

1) Am I right in thinking that receiving 69 amps when in use from the alternator is likely to damage the battery? I'm surprised the fuse hasn't blown too as it is rated at 60 Amps slow blow iirc.

2) When in use should the max draw be around the 30 amps on the charging cable?

3) Are there better options than those I'm considering?

 

TIA,

Paul.

[ditchcrawler]

35 minutes ago, PCSB said:

Hope everyone had as good a Christmas as possible. After a bit of a sanity check if possible 🤪

 

The current (no pun intended) situation is our bow thruster battery is charged via a split charge diode device from Sterling. The battery is not in great shape as it cannot supply power for very long - 10 or 15 seconds type thing. It soon flattens. Not sure if it is recoverable or not, will worry about that later. I won't replace it until I have sorted out the charging though.

 

I know that split charge diodes drop the voltage, the max I have seen at the battery end is 13.9v but when I measured that there were zero amps being drawn so indicating the battery was fully charged. After using the thruster the volatge dropped on the charging circuit to 13.1v. What was interesting was that the amperage when in use shot up to 69amps - this was on the charging cable NOT on the battery to thruster supply cable. This seems far too high to me for 110 Ah battery. I guess the split charge diode is a dumb device or the battery is goosed (or both). When not in use the amperage was around 17 or so briefly but seemed to drop off which I suspect is normal. 

 

My meter cannot read the draw from the battery to thruster as it exceeds the range.

 

I haven't yet checked the voltage from the alternator directly recently, the display in the engine control panel shows 14.5v. Next time I'm in the engine bay I'll do a quick check to confirm. The starter battery seems to be fine showing no signs of lacking power, even on the coldest days.

 

I intend to replace the split charge diode in the next month or two, I rarely use the bow thruster but its nice to have it as it can make life easier. I'm thinking of putting in something like the Victron Orion Smart DC-DC 12v 30A charger or Victron Argofet Battery Isolator. The latter would be the quicker switch as in wiring terms it looks to be a straight replacement but the Orion seems more controllable.

 

I'd like to stick with Victron kit if going the smart route as it makes life easier for me, inverter, shunt, mppt all being Victron therefore all available in one app.

 

So for the sanity check:

1) Am I right in thinking that receiving 69 amps when in use from the alternator is likely to damage the battery? I'm surprised the fuse hasn't blown too as it is rated at 60 Amps slow blow iirc.

2) When in use should the max draw be around the 30 amps on the charging cable?

3) Are there better options than those I'm considering?

 

TIA,

Paul.

What happens if you try to use the thruster with the engine stopped, Has the battery got the guts to turn it ?

[David Mack]

A voltage sensitive relay connecting the domestic and bow thruster batteries will ensure that the bow thruster battery sees the full charging voltage from the alternator (when no current is being drawn by the bow thruster). The length of wire between the two batteries (assuming located near bow and stern) will limit the current flowing between the two when the bow thruster is in operation. The interconnecting wire should be fused at both ends.

[PCSB]

8 minutes ago, ditchcrawler said:

What happens if you try to use the thruster with the engine stopped, Has the battery got the guts to turn it ?

Yes it works. Haven't tested duration as such but several 3 second blasts each way seemed ok. Battery voltage shortly after was 12.6v which I think is ok-ish.

2 minutes ago, David Mack said:

A voltage sensitive relay connecting the domestic and bow thruster batteries will ensure that the bow thruster battery sees the full charging voltage from the alternator (when no current is being drawn by the bow thruster). The length of wire between the two batteries (assuming located near bow and stern) will limit the current flowing between the two when the bow thruster is in operation. The interconnecting wire should be fused at both ends.

It's definitely fused at the bow thruster end, will have to check at the other end. 

[Sailbadthesinner]

The 69A current you are seeing is fine.

It will be going to the theater not the battery. A VSR in place of the split charge diode would give you a better charging Voltage. Otherwise I think you're OK. 15 seconds is quite a long burst of power for a bow thrusters.

 

[Tony Brooks]

Hang on. Although the OP did not give us chapter and verse on the so-called diode splitter model, I think there is a good chance that it is a so-called zero volt drop diode, basically a box of electronic gubbins that works like an electronic split charge relay. Exactly what the OP has needs clarifying because if it is not a passive split charge diode (as the OP and others seem to think) then changing it for a Victron equivalent may not be the best use of money. I would what to look at cable size etc. If the boat has an always on inverter, then a mains battery charger close to the bow thruster is another possibility.

[PCSB]

34 minutes ago, Tony Brooks said:

Hang on. Although the OP did not give us chapter and verse on the so-called diode splitter model, I think there is a good chance that it is a so-called zero volt drop diode, basically a box of electronic gubbins that works like an electronic split charge relay. Exactly what the OP has needs clarifying because if it is not a passive split charge diode (as the OP and others seem to think) then changing it for a Victron equivalent may not be the best use of money. I would what to look at cable size etc. If the boat has an always on inverter, then a mains battery charger close to the bow thruster is another possibility.

Its this model Split Charge Diodes 70 - 200A, 2 - 3 Outputs. – Sterling Power Products (sterling-power.com) specifically the 130 2 D130A2 if that helps. The table on that page seems to show voltage drops, though it is confusing (the table that is!!).

 

Also if it helps the alternator is rated at 75Amps. The splitter was installed by the boat builder fwiw, originally it split the charge from the domestic bank to bow thruster, I had them change it to starter and bow thruster. The starter is directly charged from the alternator. It has been in this configuration for a year or so now. I believe the cable is Hi-Flex 25mm2.

 

Hadn't considered a mains charger tbh, if I wet this route I believe it woud have to be permanently wired, i.e. no croc clips. Is this correct?

[Tracy D'arth]

Nothing wrong with it. It is doing what it was designed for, leave it alone.

[Tony Brooks]

1 hour ago, PCSB said:

Its this model Split Charge Diodes 70 - 200A, 2 - 3 Outputs. – Sterling Power Products (sterling-power.com) specifically the 130 2 D130A2 if that helps. The table on that page seems to show voltage drops, though it is confusing (the table that is!!).

 

Also if it helps the alternator is rated at 75Amps. The splitter was installed by the boat builder fwiw, originally it split the charge from the domestic bank to bow thruster, I had them change it to starter and bow thruster. The starter is directly charged from the alternator. It has been in this configuration for a year or so now. I believe the cable is Hi-Flex 25mm2.

 

Hadn't considered a mains charger tbh, if I wet this route I believe it woud have to be permanently wired, i.e. no croc clips. Is this correct?

 

1. That is a "zero volt drop" device but put a voltmeter between the + input and each output terminal in turn and measure the volt drop. From the data it should not be more than 0.75 volts whatever the amperage. This is to ensure it has not developed a fault. also measure the output voltages (both) terminal to negative to ensure the bow thruster side has not gone open circuit.  All the above done at 1200 rpm or more to maximise current flow.

 

2. That cable might cause excess volt drop at high current flows because of the length of run, but as the battery charges the current falls and so does the volt drop. It is likely to work well enough as long as you charge for a few hours, not an hour morning and evening. 

 

3. Yes, a charger would need permanent attachment, and it is no good unless you do have a permanently on inverter. I suspect your system should work, but the battery is sulphtaed and may even have internal shorts.

[PCSB]

2 minutes ago, Tony Brooks said:

 

1. That is a "zero volt drop" device but put a voltmeter between the + input and each output terminal in turn and measure the volt drop. From the data it should not be more than 0.75 volts whatever the amperage. This is to ensure it has not developed a fault. also measure the output voltages (both) terminal to negative to ensure the bow thruster side has not gone open circuit.  All the above done at 1200 rpm or more to maximise current flow.

 

2. That cable might cause excess volt drop at high current flows because of the length of run, but as the battery charges the current falls and so does the volt drop. It is likely to work well enough as long as you charge for a few hours, not an hour morning and evening. 

 

3. Yes, a charger would need permanent attachment, and it is no good unless you do have a permanently on inverter. I suspect your system should work, but the battery is sulphtaed and may even have internal shorts.

Thanks Tony, I'll try ad do the tests tomorrow but have a longish day cruise planned. As always your advice is much appreciated.

[Ewan123]

My bowthruster battery conks out after about 6 seconds I think. That's been the case for 3 years though it only gets occasional use.I wouldnt really want to use the thruster much more than that anyway, and at least it's preventing the thruster from dying due to overuse.

 

Is a maximum 15 seconds of thruster power really problematic/indicative of a struggling battery?

[nicknorman]

I don’t see anything much wrong with the figures and description you’ve given. The 69A is going to the thruster motor, not to the battery. The 17A is going to recharge the battery. The only thing that is non-ideal is the 13.9 charge voltage, probably a consequence of the long cables and or the diode splitter.
If it is a conventional diode splitter it would be better to replace it with a zero volt drop electronic equivalent. Or as suggested, if there is normally ac mains on the boat (usually-on inverter) then a battery charger located near the BT battery is a better idea.

[PCSB]

Thanks all. Sanity restored (well temporarily  ).

[blackrose]

8 hours ago, David Mack said:

A voltage sensitive relay connecting the domestic and bow thruster batteries will ensure that the bow thruster battery sees the full charging voltage from the alternator (when no current is being drawn by the bow thruster). 

 

Why would you split the charge between domestics and BT batteries? Isn't a better arrangement to split the charge between start and BT batteries on the basis that the start battery is more likely be topped up quicker and therefore any charge will be more readily available for the BT batteries?

 

Anyway, that's the configuration I've got and in 18 years of owning the boat I've never run out of BT battery power.

 

 

2 hours ago, Ewan123 said:

...and at least it's preventing the thruster from dying due to overuse.

 

Is a maximum 15 seconds of thruster power really problematic/indicative of a struggling battery?

 

No it's indicative of someone with a heavy finger!

 

Keeping the BT switch pressed down for 15 seconds IS overuse! I use mine in <5 second blips. <10 seconds very occasionally would be the absolute maximum.

Edited December 28, 2023 by blackrose

[Tony Brooks]

9 hours ago, Ewan123 said:

My bowthruster battery conks out after about 6 seconds I think. That's been the case for 3 years though it only gets occasional use.I wouldnt really want to use the thruster much more than that anyway, and at least it's preventing the thruster from dying due to overuse.

 

Is a maximum 15 seconds of thruster power really problematic/indicative of a struggling battery?

 

Assuming the battery is of at least 100Ah size and a starting battery.

 

As the bow thruster motor is similar to a starter motor, I would suggest that cutting out after 6 seconds is indicative of either a very poorly battery or a motor overheating problem, so next time it cuts out feel the motor case. If it is very hot then find out why. If it is cool or slightly warm, suspect the battery. Based on typical starter motor advice re fuel system bleeding, you should be able to run it in up to 30 second bursts if you really want to.

[ditchcrawler]

10 hours ago, blackrose said:

 

Why would you split the charge between domestics and BT batteries? Isn't a better arrangement to split the charge between start and BT batteries on the basis that the start battery is more likely be topped up quicker and therefore any charge will be more readily available for the BT batteries?

 

I would go along with that

[Ewan123]

3 hours ago, Tony Brooks said:

 

Assuming the battery is of at least 100Ah size and a starting battery.

 

As the bow thruster motor is similar to a starter motor, I would suggest that cutting out after 6 seconds is indicative of either a very poorly battery or a motor overheating problem, so next time it cuts out feel the motor case. If it is very hot then find out why. If it is cool or slightly warm, suspect the battery. Based on typical starter motor advice re fuel system bleeding, you should be able to run it in up to 30 second bursts if you really want to.

Thanks 👍 it's quite far down the priority list but I might have a poke around at some point. It's a gradual-ish reduction in power over a couple of seconds and it can be extended with the engine revved up in neutral, so it feels like a battery issue. 

[matty40s]

3 hours ago, Tony Brooks said:

 

Assuming the battery is of at least 100Ah size and a starting battery.

A large number of new build boats (inc some Aqualine) are being supplied with standard domestic batteries as opposed to starter batteries.

The most common problem with bowthruster batteries is the operator. Excessive use, always using them when mooring up, and then turning the boat off and walking away means the battery is never left in a fully charged state, and therefore sulphates away the capacity, reducing it after every trip.

 

[Tony Brooks]

1 hour ago, matty40s said:

the battery is never left in a fully charged state, and therefore sulphates away the capacity, reducing it after every trip.

 

I agree, sulphation seems a very likely cause.

[ditchcrawler]

2 hours ago, matty40s said:

The most common problem with bowthruster batteries is the operator. Excessive use, always using them when mooring up, and then turning the boat off and walking away means the battery is never left in a fully charged state, and therefore sulphates away the capacity, reducing it after every trip.

 

Very true, that and a poor system of charging

Edited December 28, 2023 by ditchcrawler

[Tony Brooks]

14 hours ago, blackrose said:

 

Why would you split the charge between domestics and BT batteries? Isn't a better arrangement to split the charge between start and BT batteries on the basis that the start battery is more likely be topped up quicker and therefore any charge will be more readily available for the BT batteries?

 

Anyway, that's the configuration I've got and in 18 years of owning the boat I've never run out of BT battery power.

 

 

Now more and more boats are fitting significant solar for domestic battery charging, unless they have a dual output controller, then splitting from the domestic battery may have a point. The solar would charge the bow thruster battery when the boat was left moored up.