# Connecting a 12v Control panel to a 24v Truck system

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1. May 9, 2015

### CHARLOTTE34

Help!
I am connecting a Sergent control panel (to power a motorhome 12v/240v system), with a 1200W converter for a solar panel that trickle charges a 12v battery and a leisure battery.

This would not be the problem but my truck runs on 2 batteries that run 24v.

Does anyone have an idea on how these two can be connected??

2. May 9, 2015

### insightful

Are you sure the two truck batteries aren't just used in parallel for starting only? Have you measured 24V anywhere in the truck?

3. May 9, 2015

### Svein

Get hold of some two-pole switches (with a high current rating, ask in boat accessory shops) and connect them as shown. When all the switches are in upper position, the trickle charges goes to both batteries. In the lower position, the batteries are connected for driving. Use the lower battery as a leisure battery.

4. May 9, 2015

### insightful

I think I answered my own questions. You're probably in the UK where 24V truck systems are not uncommon. Still confused; are the truck and motorhome two vehicles? If so, you want to share the solar cell between them?

5. May 9, 2015

### CHARLOTTE34

Thanks, I belive this is the case as we have measured only 12v across each battery individually.

6. May 9, 2015

### Staff: Mentor

12V across each battery individually doesn't tell you anything (except that they're 12V batteries, which we already knew). The question is whether they're connected in parallel to produce a 12V system with two battery's worth of capacity, or in series to produce a 24V system. To answer that you need to measure the voltage between the negative terminal of one battery and the positive terminal of the other, while the moor is running. If it is 24V the batteries are connected in series and you have a 24V system; if it is 12V the batteries are connected in parallel and you have a 12V system.

7. May 10, 2015

### CHARLOTTE34

Ok thankyou for that information, I will check this today.

If that is the case I have a control panel EC328, that i would like to connect to which has the facility to charge the battery when the motorcaravan engine is shut off, do you know a way of connecting the two? as in it's wiring diagram it only states connection to 1 leasure battery (which I have) and one 12v battery, not two.

Kind regards and thankyou for your patience with a layperson.

8. May 10, 2015

### CWatters

Can you confirm that you have three batteries...

The 12V leisure battery.
Two 12V batteries associated with the engine of the truck/motorhome that might be connected in series (24V) or parallel (12V).

If that's the case then...

If the two 12V batteries in the truck are connected in parallel you can treat them like one big 12V battery.

If they are connected in series to make 24 V I don't think it's possible to connect them to that control panel.

Got a photo of the two batteries? We might be able to work it out from that.

9. May 10, 2015

### CWatters

It could be a lot more complicated than that. For example if these are the main/starter batteries for the truck things like the radio may cause issues (eg need to enter PIN number each time you switch over). Any alarm system may also get unhappy.

10. May 10, 2015

### Svein

As I said - use the lower battery as a leisure battery (including radio and alarm etc.). The only thing I assume, is that the upper battery is needed for start and driving.

11. May 10, 2015

### CHARLOTTE34

Thankyou CWatters,

I shall take some photos tomorrow and post by the evening.

What you have stated above is the case, I have one leisure battery 12V and I am still to find out whether the two 12V batteries associated with the engine are 12v or 24v,

but the truck is running now so tomorrow i hope to measure the voltage across the two batteries to determine this.

Thanks again

12. May 11, 2015

### CWatters

Ah ok yes I misunderstood.

If it's a 24V system it should be possible to use your circuit in post #3.

13. May 11, 2015

### CHARLOTTE34

Thankyou.

14. May 11, 2015

### Svein

A slightly simpler version. Both switches in the lower position: Trickle charge both batteries. Both switches in the upper position: 24V for driving. The diodes must be able to block 30V and conduct the trickle charge. The lower battery is still used as a leisure battery.

15. May 11, 2015

### CWatters

I think your first version might be better. The control panel Charlotte mentioned can use the vehicle battery to power the mobile home when the 12V leisure battery in the mobile home is low.

Edit: The diodes may also mess with the charging. Looks like it changes the charge current depending on the battery voltage. Para 3.2..

http://www.sargentltd.co.uk/EC328_User_Instructions.pdf [Broken]

Last edited by a moderator: May 7, 2017
16. May 11, 2015

### CHARLOTTE34

To all,
I have found it is a 12v battery set (x2) connected in parallel.

I now have the continuing task of connecting the system,

Thankyou to all for your knowlege and help.

It is most appreciated.

Kind regards
Charlotte34

17. May 11, 2015

### CWatters

That should make life a lot easier.

18. May 11, 2015

### CHARLOTTE34

Oh dear.....I was given misinformation and on checking myself again...

I have not been able to use a multimeter over the batteries, but I have checked a couple of lamps and they are rated at 24v.

So from this I gather I have a 24v truck system.

19. May 11, 2015

### Staff: Mentor

Not necessarily. A 24v-rated lamp will glow if you apply 12v. Test lamps are not for measuring unknown volatges, they're for detecting the presence or absence of known voltages.