24v from 12v

[martynwhiteley]

Having just acquired a 24volt Eberspacher truck heater for the price of a couple of pints, I'm determined to install it in my 12volt Birchwood.

The 3 options I seem to have are:-

1. Convert the unit to 12v.

However I've viewed past posts to confirm my belief that this conversion would not be cost effective.

2. Somehow convert the 12v supply to 24v.

Haven't been able to find any device listed to do this, however suspect I could go from 12v to 230v ac, then back down to 24v. But to end up with a minimum of the 40w required by the Eberspacher would mean sizeable power supplies, and again I think the cost would begin to get a bit silly.

3. Install an extra battery.

I believe this is likely to be the way to go, but has anyone any successful experience of this option, and know any novel ways of overcoming the chargeing hassle.

Any advice would be appreciated.

 

[paulineb]

Isn't there a 24v to 12v step down transformer you can use?

Pxx

<A target="_blank" HREF=http://www.paulinebeddoes.co.uk/php-cgi/gallery>http://www.paulinebeddoes.co.uk/php-cgi/gallery</A>

 

[tr7v8]

It's complicated using relays and in the days when we did it on rally cars bloody dangerous, if a reay is a bit slow then bang!
I've heard of another way which is using car headlight bulbs. Add second battery and connect positive of this to load heater whatever, also couple a car headlight bulb from this positive to the existing pos. another goes between the neg of new battery to neg of existing. A switch is used between the neg of new to pos of old which is closed only when you want the heater on. This could be done by a relay driven from the heater on switch. Drawing is at:-
http:// http://www.yandina.com/24VoltBattery.htm
What happens is that the running current of the headlamps go through the headlamp bulbs and the charge current can also do that.

Jim
---------

 

[pistonbroke]

Read the post properly you soppy mare.

 

[andyball]

wd think you'll need more than 40W to get an eberspacher started.....maybe 40W is for once it's heated/started?

For the lowish (20Amps?) requirements of a 24V diesel heater, a DPDT (changeover) switch can be used to connect two batteries in series (24V) or parallel (12V),tho' the second battery won't charge when being used for the heater.

Index marine seem to sell 20Amp rated dpdt toggle & rocker switches......you'll need a decent battery set-up,since some heaters are very juicy on pre-heat & won't fire up w/o a good 25V.

If you can test the heater using two batteries, & measure the current needed/time to warm up....you'll be better able to decide what to buy.

 

[Strathglass]

This might sound a bit of a roundabout way, but it is quite cost effective and will work well with minimum alterations to the boat wiring.

There are on the market low cost 12 volt emergency power packs.
They are plastic cased and contain a 12 volt 7 ampere hour sealed lead acid battery. I purchased one from the local LIDO store for under £15, this included a 240 volt mains charger. There are terminals to provide a direct 12 volt output which bypass the cigarette lighter socket.
This gives you the top up 12 volts which can be added to your domestic 12 volts to give the required 24 volts.

You will also need to charge the battery and to do this purchase the lowest cost 12 volt to 240 volt inverter you can find ( under £50 ) and run this from your domestic 12 volt battery.

Your invertor can be used for other tasks in addition to keeping the add on 12 volt charged. It need only be run when the heater is on.

The inverter will be isolated as will the charger for the 12 volt add-on, thus the new 12 volt battery will also be floating.

Mount the add on 12 volt supply near the Eberspacier to keep lead length down.

A bit of a twisted way to get a 24 volt supply but by using mass produced 'non marine' items it can be quite cost effective.

Hope this helps

Iain

 

[martynwhiteley]

Thanks Iain,

That seems like an excellent solution, and would you believe, I picked up prob the same 12v power pack from Lidle for £14.99 some weeks ago (still in its box waiting for a use)!

Your reply was only surpassed by Pauline b, I'm not bothered about the wrong-end of-the-stick-advice, but having passively read many posts from the regular crew over recent months, It feels like meeting a celebrity, having a response from Pauline. Mind you, half expected one from Byron advising the correct size of selotape to use to repair the Birwood wiring!

Thanks to all repondees....(past and future...)

 

[ChrisP]

Can't use a tranni for DC to DC conversion. Need ocilator to chop the current.

What do you mean the sea gull in front's walking !!!

 

[Strathglass]

Yes you can. That is how the PSU in a PC works. The AC in is rectified to give a sort of DC. This is then switched by transistors to give a higher frequency AC signal (for better efficiency) which is fed through a transformer to give the voltages the required by the PC. The ac outputs are then rectified and filtered to give the DC voltages. The +5 volts level is used to control the pulse width of the 'on' time of the high frequency AC signal to regulate the + 5 volt supply.
These are very small, efficient, low cost and reliable mass produced boxes but initially they were very far from that.

The design of a DC to DC convertor is not rocket science but The design of a reliable one off box with no follow up production could not be financially justified.

I may be wrong of course and a design may already be available, but the surge load imposed by the glow plug in a diesel heater are very high. The design could be quite difficult.

 

[andyball]

ChrisP: "... ocilator to chop the current ";

iainsimpson: " ...DC. This is then switched by transistors ...."


Wd think you're both talking about excatly the same thing there.

 

[stefan_r]

try:
01202 60 37 42 merlin electrics
or yachtbits.co.uk

they have been very useful to me in the past - alternatively sell me the Eberspacher cos I am on a 24v system already!!


mailto: stefan@athito.com