A simple all-in-one DC-DC charging system – viable?

[CaneyJ]

My current boat is small in size and currently has a small starter battery fed from a Beta 28 engine driving a 65-Amp alternator. It manually splits to a pair of 85AH leisure batteries in parallel via a rotary selector switch.

 

The leisure batteries are also charged via a CTEK 15-Amp mains charger when on shore power and there is also a 600-Watt Pure sine Inverter drawing off them occasionally.

 

I've been considering adding 200 to 300 watts of solar along the entire top of the roof feeding a 15-Amp MPPT controller. I've also been looking at updating the charging system as well since the volts my alternator puts out is vairable between 13.9V to 14.2V and not giving the batteries a complete engine charge.

 

The current leisure set are also getting a bit old so I want to upgrade to a pair of T105 trojans which need 14.8 Volts to get to full charge.

 

Whilst looking at updating the DC systems and looking at Sterling kit, I also happened upon this item linked below:

http://www.ebay.co.uk/itm/Ring-DC-Solar-Battery-Charger-30A-Split-Charge-System-Leisure-Batteries-RSCDC30-/231684355262?hash=item35f176b4be:g:xVsAAOSwFnFV8oBi

 

Instead of using a seperate AC charger, instead I was thinking of using a 400-Watt switched AC-12VDC [slight output variable] power supply. Since it's only 400-Watts; this can be driven from a small and crude generator like an EX650 but also give enough for the full 30-Amp multi-stage charge. The slight variation on the output allows it to put out upto 13.9V which is enough to activate the Battery-to-battery charger.

 

It could be connected into the same input terminals as the alternator cables and end in a 50-Amp anderson plug which is then connected to the AC supply and generator when required.

 

http://www.ebay.co.uk/itm/DC12V-400W-33A-Switching-Power-Supply-115V-230V-to-Stepper-Motor-3D-Printer-CNC-/121684006529?hash=item1c54ee9681:g:Mj4AAOSw~gRVjj1W

 

It seems to allow adjustable voltage outputs with the mention of it's default output being 14.8V and also integrates an MPPT solar controller.

 

This means I can get a decent setup for around £200 and cut down on the number of components. Would this idea be viable?

 

Here's a wring diagram of the concept below

 

 

[Nickhlx]

I use these power supplies but would not suggest using them as a charger as they ( mine) are constant voltage and not current limited. In anything other than a high state of charge, the batteries would draw more than the power supply could handle and any overheat / protection device would be constantly tripping ...

 

Nick

[MtB]

I use these power supplies but would not suggest using them as a charger as they ( mine) are constant voltage and not current limited. In anything other than a high state of charge, the batteries would draw more than the power supply could handle and any overheat / protection device would be constantly tripping ...

 

Nick

 

 

Does that mean you actually understood the original post?!

 

[Nickhlx]

Maybe not from your inference - I am not familiar with the functions built in to a battery-battery charger so do not know if they have a current limiting function within them - my point was that the AC to "12V" unit does not have this and if more is attempted to be drawn for any period, it will get (too) hot...

[Phil Ambrose]

I have a Sterling battery to battery charger and according to Sterling it is current limited.

Phil

[CaneyJ]

The maximum output of the B2B Charger is 30-Amps and the alternative input AC-DC switching power supply I suggested was rated at 33-Amps but they also offer 500-watt and 600-Watt (50A) versions for not much extra cash and there must be a cutoff on the maximum input.

 

I'm more interested in top-end multi-stage voltage output than raw amps in the first hour of charging or I'd get a volt-sebsitive relay.

[dmr]

A novel way of drawing a circuit diagram!

The concept looks ok but that DC power supply looks very cheap and cheerful. I would be a bit cautious about very cheap power electronics for both reliability and fire risk. The 13.9v maximum is a bit low for charging the starter battery.

Also the battery-battery charger really needs to utilise the full output of the alternator to avoid excess engine running hours, raw amps early on is important!

There is a very very small chance that the PSU and B2B will not like each other.

 

..........Dave

[by'eck]

Sounds like you are complicating the installation rather than simplifying. Suggest as a starting point fitting an external alternator regulator to get the engine driven charge voltage up to 14.8 volts with added advantage of battery sensing and float mode when fully charged. If feeling brave and to save money you could achieve similar charge voltage increase with a diode mod as here.

[WotEver]

I'm more interested in top-end multi-stage voltage output than raw amps in the first hour of charging...

This sentence makes no sense to me.

[Tony Brooks]

I have a Sterling battery to battery charger and according to Sterling it is current limited.

Phil

 

Personally I would want to see the circuit diagram before I believed it had any current limiting circuitry apart from overheat protection that marketeers may claim as current limiting.

 

I think that we are back to the fact that under NORMAL operating conditions as the current from a given charging source rises the maximum voltage it can produce falls. This is to do with internal design and not special circuits. As a (say) 30 amp source approached 30 amps the voltage starts to fall so by 30 amps the voltage will be low enough to prevent the charging current flowing being any higher than 30 amps.

 

If you short the charging leads out then hopefully the device will protect itself (blow a fuse! - that's current limiting but not what I understand by the term).

 

I know Nick has put forward a differing view and I do not know how switched mode chargers react to increasing charging currents apart from getting hotter so maybe modern chargers really do have current limiting circuits but over the years the marketing departments across many sectors have pushed so many half truths puffing up natural features I believe few of them. An example is the need to give charging the engine battery priority over the domestic bank.

[Phil Ambrose]

 

Personally I would want to see the circuit diagram before I believed it had any current limiting circuitry apart from overheat protection that marketeers may claim as current limiting.

 

I think that we are back to the fact that under NORMAL operating conditions as the current from a given charging source rises the maximum voltage it can produce falls. This is to do with internal design and not special circuits. As a (say) 30 amp source approached 30 amps the voltage starts to fall so by 30 amps the voltage will be low enough to prevent the charging current flowing being any higher than 30 amps.

 

If you short the charging leads out then hopefully the device will protect itself (blow a fuse! - that's current limiting but not what I understand by the term).

 

I know Nick has put forward a differing view and I do not know how switched mode chargers react to increasing charging currents apart from getting hotter so maybe modern chargers really do have current limiting circuits but over the years the marketing departments across many sectors have pushed so many half truths puffing up natural features I believe few of them. An example is the need to give charging the engine battery priority over the domestic bank.

Tony, my comment about the Sterling B2B charger that I have being limited was only what Charles told me himself, I have no idea how it works just that it does.

Phil

Edited January 4, 2016 by Phil Ambrose

[Tony Brooks]

I would not trust the person named to tell the whole un-gilded truth - or his marketing department. That is not to say it does not have current limiting circuitry but until it is independently proven to have I will remain sceptical. I think the B2B uses circuitry similar to switched mode power supplies and I have already said I am not sure how they work.

 

My post was not directed against what you said, you can only say what you are told, it was more of a warning no to believe everything sales brochures etc try to imply or even state.

[Phil Ambrose]

I would not trust the person named to tell the whole un-gilded truth - or his marketing department. That is not to say it does not have current limiting circuitry but until it is independently proven to have I will remain sceptical. I think the B2B uses circuitry similar to switched mode power supplies and I have already said I am not sure how they work.

 

My post was not directed against what you said, you can only say what you are told, it was more of a warning no to believe everything sales brochures etc try to imply or even state.

Appreciate that your remarks were not directed at me and yes you are right to point out that all we are told may actually differ from the truth (sometimes)

Phil