24v to 12v step down to charge 12v batteries?

[Sy-Revolution]

Hi Folks,
Not strictly boaty but one for the DC gurus .....

I have a lorry that's 24v and a 12v solar system, I'd like to charge my 12v batteries from the lorry. I've got a 100 amp 24v to 12v step down but it's not designed for battery to battery charging. Is there something that I can add to the 12v out on the step down to enable it to be used as such, (diode??) or is it an entirely different animal?

Can anyone enlighten me?

Cheers,
Crispin

 

[Refueler]

Look at Charge Controllers, even such as Solar / Wind ... as often the voltage range they can use is wide enough and the 12v out .. actually more like 14+ is regulated by charge state determined of battery.

 

[PaulRainbow]

Not 100% certain what it is you're doing, but you cannot use a DC-DC converter to charge the 12v battery, it will only output 12v, which isn't enough volts for charging.

You need a battery to battery charger.

A bit more detail about what it is you are doing might help.

 

[Alex_Blackwood]

Not 100% certain what it is you're doing, but you cannot use a DC-DC converter to charge the 12v battery, it will only output 12v, which isn't enough volts for charging.

You need a battery to battery charger.

A bit more detail about what it is you are doing might help.

+1 for that. Also is his 24-12 definitely DC , not an ac transformer by any remote chance?

 

[Sy-Revolution]

Look at Charge Controllers, even such as Solar / Wind ... as often the voltage range they can use is wide enough and the 12v out .. actually more like 14+ is regulated by charge state determined of battery.

I had thought about using a solar charge controller as they're much cheaper but my concern would be the amperage of the 24v alternator, would have to be a hefty controller to cope?

 

[Alex_Blackwood]

I had thought about using a solar charge controller as they're much cheaper but my concern would be the amperage of the 24v alternator, would have to be a hefty controller to cope?

Amps out from the alt. will be limited by what the battery can take / requires.

 

[geem]

Look at Victron battery to battery chargers. They make one that will charge a 12v battery from your 24v battery for about £250. 30A charging. I have one on my 24v boat to charge my 12v genset battery

 

[Refueler]

I bought this :

10/20/30A Solar Charge Controller For 12V/24V Panel Dual Battery Regulator Kit | eBay

Accepts up to 41V (Solar) .... so I reckon a 12 / 24V standard car battery charger / regulated Power supply should not be problem.

I would connect your "I've got a 100 amp 24v to 12v step down " DC - DC 24V adaptor to power it rather than straight of alternator. The controller will only take what batterys demand

Still waiting suitable weather to go down to boat to fit ... but others have reported it works fine ...

 

[PaulRainbow]

I bought this :

10/20/30A Solar Charge Controller For 12V/24V Panel Dual Battery Regulator Kit | eBay

Accepts up to 41V (Solar) .... so I reckon a 12 / 24V standard car battery charger / regulated Power supply should not be problem.

I would connect your "I've got a 100 amp 24v to 12v step down " DC - DC 24V adaptor to power it rather than straight of alternator. The controller will only take what batterys demand

Still waiting suitable weather to go down to boat to fit ... but others have reported it works fine ...

Can you feed 12v into a PWM controller and get 14.4v out ?

 

[Refueler]

Can you feed 12v into a PWM controller and get 14.4v out ?

Probably not .... but in my case I am inputting from a charger that will be higher than that - so I expect to see it work. If not - then I shall be looking to add a solar panel .... total cost still less than half a Victron.

PWM .... there are in fact Step Down and Step UP PWM controllers as what its doing is basing on the WATTS rather than just Volts.

Problem with lower end single stage PWM is that they are designed to switch on / off to reduce the averaged power output. In effect Step Down only. They require a higher input voltage so they can actually regulate the pulse based on the battery state.

But if he can sort connecting the 24V to it .... then ??

 

[LadyInBed]

I used a Mobitronic Voltage converter/charger from 24 to 12 Volts, 18/15A - 818-2412L
I have now done away with the 24v battery system so the converter/charger is now spare.
PM me if interested.

 

[Sy-Revolution]

My battery bank is 900amh, 8 x Trojan T105s. However, I'll have 700watts of solar feeding them and I never let them drop below 12.2v.

Might well try the pwm solar controller route. Thanks

 

[VicS]

My battery bank is 900amh, 8 x Trojan T105s. However, I'll have 700watts of solar feeding them and I never let them drop below 12.2v.

Might well try the pwm solar controller route. Thanks

IF you are thinking of adding that to your 24v to 12v converter it wont work because normally they wont increase the volts to the 14 or so needed for charging. Theoretically its possible but I dont know if you will actually find one that will do that. Solar panels for 12 volt systems have a open circuit volts over 20 and the specified power is produced when the terminal volts is around 17 or so volts.

 

[William_H]

Presumably you only want to recharge from Lorry when solar has failed due to lack of sun. I would suggest you first check with a volt meter the actual voltage out of your 24v to 12v converter. I have one here that delivers 13.75 volts. (not 12v) If that is the case you might find that it delivers adequate charge for your purposes. An amp meter to confirm actual charge would be most useful. I don 't think you could add a diode in negative side of supply to increase voltage as you might in some systems.
You might find a voltage adjustment inside the converter which may facilitate increase of voltage so increase charge current. Other wise you need a converter set up as a charger with stepped charge voltage. However you might also find that an MPPT solar regulator like Victron will convert and charge in stepped manner. Or just buy from China a stepdown regulator with adjustable output voltage. (With no current/voltage reduction when fully charged.) DC-DC 8V-60V TB 1-36V 200W 15A 12V Voltage Power Buck Converter Step Down Module | eBay
No a PWM controller would be bad. It does not have the "flyback inductor/diode" that a regulator has. ol'will

 

[Refueler]

As Will says - many so called converters actually produce higher open voltage than listed. Its when connected to the intended load that the voltage settles to listed.
In fact - you can test this yourself - many power adaptors if you just put probes to leads without a load - show literally zero or only slight voltage. Only when a load is connected - does the adaptor then come to life.
This is one of the reasons that most solar controllers should be connected to the batterys before connecting the power source - ie panels.

I am not sure whether the Solar Controller I have in hand will do OP"s or my intended ... but I also know that all my battery chargers for my model activities powered from 12V PSU's are PWM based and charge up to 6S packs ... that's 6 x 4.2V ..... 25.2V.

Its a shame that weather is so foul out there - otherwise I could solve this quickly with regard to the controller I suggested.

OP has source of 24V ... with care - I would expect the Solar controller to accept that and provide charge out ... as its above the threshold voltage .... but first as a precaution - I would try the 24 to 12v adaptor ... see what happens. Just playing safe.

There are other ways of course ..... online sellers such as Banggood have small adaptors that accept user settable voltage in ... with user settable voltage out - with auto shut off when charge state reached. They are not expensive either ...

 

[geem]

The advantage of using a proper B2B charger is you get a bulk, absorption and float charge profile ideal for you batteries. These voltages are programmable to meet the battery manufacturers recommendations.

 

[Refueler]

The advantage of using a proper B2B charger is you get a bulk, absorption and float charge profile ideal for you batteries. These voltages are programmable to meet the battery manufacturers recommendations.

As with most systems ........

Having been a Caravan owner as well as Boats ...... the world is much wider than just the 'Marine' designated gear ....

My last caravan .... 16ft. Had a full Carver system installed ............ not something that comes cheap.

It had automatic change from Car power (during tow) to Caravan Battery (unplugged) ,,,, automatic change from Caravan Battery to Mains supply if plugged into site. It monitored batterys - 2 batterys - on board and had individual displays.
It controlled all power distribution - even the mains electric AND the Hot Water heater which used Mains or Calor Gas ....

When I look back all those years ago - that was late 90's and read what people suggest for boats - I understand there's still a long way to go !!

 

[geem]

As with most systems ........

Having been a Caravan owner as well as Boats ...... the world is much wider than just the 'Marine' designated gear ....

My last caravan .... 16ft. Had a full Carver system installed ............ not something that comes cheap.

It had automatic change from Car power (during tow) to Caravan Battery (unplugged) ,,,, automatic change from Caravan Battery to Mains supply if plugged into site. It monitored batterys - 2 batterys - on board and had individual displays.
It controlled all power distribution - even the mains electric AND the Hot Water heater which used Mains or Calor Gas ....

When I look back all those years ago - that was late 90's and read what people suggest for boats - I understand there's still a long way to go !!

Victron isn't just marine gear. They produce equipment for off grid and RV use. Its all the same stuff. No marine designation to it. What point are you trying to make?

 

[Refueler]

Victron isn't just marine gear. They produce equipment for off grid and RV use. Its all the same stuff. No marine designation to it. What point are you trying to make?

Point ? Often same gear at Caravan Dealer is significantly cheaper ... wider ranging than the Chandlers ............

 

[geem]

Point ? Often same gear at Caravan Dealer is significantly cheaper ... wider ranging than the Chandlers ............

So what piece of caravan kit would install that's appropriate in this instance?