24v on 12v system??

[vasant]

Hi
This is more an academic question i understand buying a DC converter is the clean way to go , BUT
If i have a 24V appliance on my boat could i connect the + to the service battery and the MINUS to the starter when connecting the other two poles in series while all other applinces are served from each battery on 12v?
Just wondering what can go wrong....

 

[oldmanofthehills]

To enable the batteries to be charged by the alternator, they must have a common earth (negative) with each positive fed from common alternator output either by splitter diode or VCR.

So there is no way to connect them in series as they are already in semi-parallel

 

[chriscallender]

Hi
This is more an academic question i understand buying a DC converter is the clean way to go , BUT
If i have a 24V appliance on my boat could i connect the + to the service battery and the MINUS to the starter when connecting the other two poles in series while all other applinces are served from each battery on 12v?
Just wondering what can go wrong....

That would only work if currently the starter wiring and the service wiring are completly independent of each other. For instance, if the negiative of both systems is currently connected to an anode or other common ground point (even indirectly - for example through the engine - it might not be completely obvious ) then you come along and connect the two batteries in series you have just shorted out one of the batteries because you will connect the positive terminal of one of them to the negative terminal of the other which is actally the negative of both.

The other issue is charging - if you want to charge them off a 12v alternator they need to be in parallel, or one at a time for charging. So you need some switching scheme that allows you to get rid of the series connection.

If the 24v appliance doesn't need much power then a non grounded small 3rd battery in series with the 12v house battery would be easier than messing with the starter battery. But you'd still need to switch it to be paralleled for charging and forget powering your 24v appliance while charging battery #3.

But then if the 24v appliance doesn't need much power a DC-DC converter is cheap as chips, so definitely not worth the bother.

https://www.amazon.co.uk/Youmile-Converter-Adjustable-Voltage-Regulator/dp/B0C5HXZ6HT

It all depends how much juice you need at 24v. Bur regardless, it is almost always more trouble than it is worth unless the whole system is 24v, so as you say its an academic question. Even powering a diesel heater glowplug off 24v would be straigtforward with a DC-DC boost converter from 12v.

Chris

 

[oldmanofthehills]

That would only work if currently the starter wiring and the service wiring are completly independent of each other. For instance, if the negiative of both systems is currently connected to an anode or other common ground point (even indirectly - for example through the engine - it might not be completely obvious ) then you come along and connect the two batteries in series you have just shorted out one of the batteries because you will connect the positive terminal of one of them to the negative terminal of the other which is actally the negative of both.

The other issue is charging - if you want to charge them off a 12v alternator they need to be in parallel, or one at a time for charging. So you need some switching scheme that allows you to get rid of the series connection.

If the 24v appliance doesn't need much power then a non grounded small 3rd battery in series with the 12v house battery would be easier than messing with the starter battery. But you'd still need to switch it to be paralleled for charging and forget powering your 24v appliance while charging battery #3.

But then if the 24v appliance doesn't need much power a DC-DC converter is cheap as chips, so definitely not worth the bother.

https://www.amazon.co.uk/Youmile-Converter-Adjustable-Voltage-Regulator/dp/B0C5HXZ6HT

It all depends how much juice you need at 24v. Bur regardless, it is almost always more trouble than it is worth unless the whole system is 24v, so as you say its an academic question. Even powering a diesel heater glowplug off 24v would be straigtforward with a DC-DC boost converter from 12v.

Chris

Heaven, what a receipe for disaster. Though I think one could arrange such switching to be applied at the point of using the 24V, there is clear risk that if switching fails one battery is shorted out and destroyed, or if effective and forgotten one battery fails to charge and engine cannot be started from it - which means no alternator and no way to get electric back except jump pack.

Of course a complex auto control system could be devised and all wiring modified, but it would be invasive, possibly expensive, and probably beyond the capability of the OP. What is more it leaves the 24V system use capable of flattening the engine starter battery thus resulting in the earlier mention failure situation

DC to DC converters from aux battery by comparison are cheap and easy

 

[Refueler]

Simple answer is NO.

 

[chriscallender]

Heaven, what a receipe for disaster. Though I think one could arrange such switching to be applied at the point of using the 24V, there is clear risk that if switching fails one battery is shorted out and destroyed, or if effective and forgotten one battery fails to charge and engine cannot be started from it - which means no alternator and no way to get electric back except jump pack.

Of course a complex auto control system could be devised and all wiring modified, but it would be invasive, possibly expensive, and probably beyond the capability of the OP. What is more it leaves the 24V system use capable of flattening the engine starter battery thus resulting in the earlier mention failure situation

DC to DC converters from aux battery by comparison are cheap and easy

Indeed. The OP asked an academic question so I tried to answer it. I agree with you, there's plenty to go wrong. It might have made sense 30 or more like 40 years ago, but it would be a silly way to get a 24v applicance to work in 2025 when you can get DC-DC boost converters for a few quid. Don't do this old school approach!

 

[Refueler]

Indeed. The OP asked an academic question so I tried to answer it. I agree with you, there's plenty to go wrong. It might have made sense 30 or more like 40 years ago, but it would be a silly way to get a 24v applicance to work in 2025 when you can get DC-DC boost converters for a few quid. Don't do this old school approach!

Old School approach ??

Its just plain wrong ... and would create more problems than the single its supposed to solve.

 

[rogerthebodger]

I have an issue in that I have a 12 DC boat but T have 2 48ST 24 Vdc electric winches that I would like to power

I will have solar charging and thinking of charging the 2 series 12 V batteries with independent solar panels or I could keep the 2 battries separate yet use only one for the rest of the domestic setup with maybe 12 Vdc batteries in parallel for the 12Vdc domestic bank and just one 12Vdc in series to give 24Dc for the winches

 

[oldmanofthehills]

I have an issue in that I have a 12 DC boat but T have 2 48ST 24 Vdc electric winches that I would like to power

I will have solar charging and thinking of charging the 2 series 12 V batteries with independent solar panels or I could keep the 2 battries separate yet use only one for the rest of the domestic setup with maybe 12 Vdc batteries in parallel for the 12Vdc domestic bank and just one 12Vdc in series to give 24Dc for the winches

Thats more like it. A third winch only battery with 3 way split rectifier charging to it from alternator along with aux and engine bat. Then all one needs is a break before make changeover switch that switches the neutral on the winch battery, to join instead to the positive of the normal auxiliary and take the positive of the winch bat to drive the 24v winches

If you fail to switch over when using winches they will grind along at one quarter power (if at all) - if you switch over they will go. The add on battery if only for the winch could be less AH than the main aux. You just have to remember to switch back or engine wont charge winch bat

One issue there is that most shore battery chargers only have two outlets so winch bat will risk going flat until engine on. However though it seems extravangent to dedicate a solar panel to charging the winch bat, you could

The alternator should not mind still being nominally connected to winch battery after changeover as a/ its a diode so no back current from 24v and b/ it then has no reference earth so now floating. It might be harder with VCR not diodes but b/ might still apply

 

[PaulRainbow]

Thats more like it. A third winch only battery with 3 way split rectifier charging to it from alternator along with aux and engine bat. Then all one needs is a break before make changeover switch that switches the neutral on the winch battery, to join instead to the positive of the normal auxiliary and take the positive of the winch bat to drive the 24v winches

If you fail to switch over when using winches they will grind along at one quarter power (if at all) - if you switch over they will go. The add on battery if only for the winch could be less AH than the main aux. You just have to remember to switch back or engine wont charge winch bat

One issue there is that most shore battery chargers only have two outlets so winch bat will risk going flat until engine on. However though it seems extravangent to dedicate a solar panel to charging the winch bat, you could

The alternator should not mind still being nominally connected to winch battery after changeover as a/ its a diode so no back current from 24v and b/ it then has no reference earth so now floating. It might be harder with VCR not diodes but b/ might still apply

The vast majority of shore chargers are either 1 or 3 outlets, 2 outlets is very, very rare.

Other than that, this sounds like a complete bodge compared to a dedicated pair of batteries in series, charged by a DC-DC charger.

 

[oldmanofthehills]

The vast majority of shore chargers are either 1 or 3 outlets, 2 outlets is very, very rare.

Other than that, this sounds like a complete bodge compared to a dedicated pair of batteries in series, charged by a DC-DC charger.

Roger did not suggest having two extra batteries, so I took him at his word. Who knows how much space he has. There is always more than one solution, and always cost constraints. Mine would work on one battery, one switch and one 3 way diodes block. I reckon £50 plus small battery yours is over twice that

He doesnt have to do it, but parallel series switching is standard technology in controls etc etc. Before your time maybe but not before mine

 

[PaulRainbow]

Roger did not suggest having two extra batteries, so I took him at his word. Who knows how much space he has. There is always more than one solution, and always cost constraints. Mine would work on one battery, one switch and one 3 way diodes block. I reckon £50 plus small battery yours is over twice that

He doesnt have to do it, but parallel series switching is standard technology in controls etc etc. Before your time maybe but not before mine

He said "thinking of charging the 2 series 12 V batteries with independent solar panels". Which involves 2 batteries, a solar controller and some solar panels. A DC-DC charger would cost less. But, as you say, more than one way of doing it....

 

[MontyMariner]

I used to have a dual voltage system with two 12's & a 24v bank, two altinators, it was a nightmare.
I ditched the 24v alternator, integrated the batteries from the 24v into the 12v banks and installed a 12 to 24v converter to supply the 24v equipment.
It works very well, I wish that I had done it years ago.

 

[rogerthebodger]

Roger did not suggest having two extra batteries, so I took him at his word. Who knows how much space he has. There is always more than one solution, and always cost constraints. Mine would work on one battery, one switch and one 3 way diodes block. I reckon £50 plus small battery yours is over twice that

He doesnt have to do it, but parallel series switching is standard technology in controls etc etc. Before your time maybe but not before mine

initially I would have one battery of parallel bank to supply 12 vdc domestic supply and a single extra battery wired in series with the domestic bank to provide 24 vdc for the winch power.

No series /parallel switching

Domestic 12v bank charges with engine alternator and or solar and the extra series battery with a single solar 12vdc panel with isoulated supply just to keep the additional battery topped up.

I live where the sun always shines

I have lodes of space for large battery banks close to winches and engine room.

 

[William_H]

I have an issue in that I have a 12 DC boat but T have 2 48ST 24 Vdc electric winches that I would like to power

I will have solar charging and thinking of charging the 2 series 12 V batteries with independent solar panels or I could keep the 2 battries separate yet use only one for the rest of the domestic setup with maybe 12 Vdc batteries in parallel for the 12Vdc domestic bank and just one 12Vdc in series to give 24Dc for the winches

Roger I would fit the electric winches and simply try them on 12v. Unlike a resistive load a DC motor has a high current at low speed that may mean enough torque on 12v. If you are not happy with that then 2 smaller batteries with a boost converter off the 12v system as a charger would work well next to solar panels for 24v battery if you have room for them.
Regarding switching batteries to parallel and series. One aircraft I had contact with (gulfstream 1000) had 2 x 24 v batteries. Normal charge arrangements. However on starting the Garret TPE 331 engines (turbine) the start sequence began with 24v on starter. (both batteries) As RPM increased the batteries were switched to give 48v to get current higher at higher RPM. You can imagine the high current switching arrangements. All do able. (turbines like lots of RPM on start for large air flow cooling) Switching reverted back to 2 batteries in parallel after start.
ol'will

 

[rogerthebodger]

Thanks, will

I did consider a switching arrangement only when the winches are operated ut having lots or room and I go for the KISS.

DC to DC would be OK if I could get a big enough unit.

I did test the motors on 2Vdc and the worked but too slow.

I also looked it there was a way to motors to run on 12VDC

Do you have any details of the switching arrangement on the gulfstream for my consideration

 

[William_H]

No actual details Gulfstream switching except it is fairly straight forward. In that one battery (2nd) must be disconnected both positive and negative from the resting charging connections. The negative is then connected to the base battery positive and the positive becomes 24v (48v) output. This latter can be connected permanently giving 12v on charge 24v when activated. You can use a relay with change over contacts or 2 relays. The connection of the positive to the base battey positive can be just a make contact relay. Or better a changeover (spdt) using the contacts at rest for connection for charge. Use a switch at the winch to activate the 24v change over.
ie make the switch, the negative relay switches the negative of 2nd battery from base battery negative to base battery positive. The positive relay switches the 2nd battery positive away from the base battery positive. That positive terminal becomes 24v.
Timing of the relays may become a problem as potentially you have a short across a battery if contacts do not operate simultaneously.
If you choose to use switches instead of relays always operate the positive switch first disconnecting 2nd battery positive from base battery positive.
I hope I have not confused you Roger. I may have confused myself. ol'will