24v supply

[stumog]

Hi

I have maybe got a nice 24v compressor from a merc lorry/bus i know they are good as they run all the air brakes doors.

I am needing to find where to take the 24v supply from should i take it from the starter not sure if its go a permante 24v supply or just when it turns over?

If i connect up the + from one battery to the - of the other will this put 24v's up everything else that is meant to be 12v?

any other idea would be good

thanks
stu

 

[grantw]

I'm pretty sure it's only when starting. Easy to test with a multi meter though.

Connecting the positive to one battery and the negative to another will still only give you 12v normally and 24v whilst starting.

You really need something like this http://www.ebay.com/itm/WaterProof-...ep-UP-Power-Converter-Regulator-/301009537870 probably at a lot higher than 10amps @ 24volts.

 

[stumog]

to get a 24v supply you normally connect 1 + to the - of the other then out of other + you will get 24v just the same as a lorry set up.

 

[Jon Wildsmith]

yep, only 24v during starting, the rest of the time the starter cable is at 12v. You could rig it to change over on a switch just when you need your compressor without the starter firing but there may be other side effects as a few things are inhibited when the changeover solenoid is active.

 

[grantw]

to get a 24v supply you normally connect 1 + to the - of the other then out of other + you will get 24v just the same as a lorry set up.

I thought you meant connect the compressor itself this way. Then you would only get 24v when starting if you connected the positive to the l/h side battery. If you connected the batteries themselves like that (in series) then you would blow all the electrics in your car!

 

[Jon Wildsmith]

to get a 24v supply you normally connect 1 + to the - of the other then out of other + you will get 24v just the same as a lorry set up.

That's what the change over solenoid does temporarily for starting. I doubt it is rated for continuous use like that and would cause other complications doing that anyway like only the passenger side battery being charged.

 

[stumog]

I thought you meant connect the compressor itself this way. Then you would only get 24v when starting if you connected the positive to the l/h side battery. If you connected the batteries themselves like that (in series) then you would blow all the electrics in your car!

I understand what you are saying grant what i was thinking is if you ran seperate wires in a stand alone system?

 

[grantw]

I'd say what Jon says pretty much kills any idea of it.

Do you know how many amps the compressor is? The step up convertor is your only real solution.

 

[stumog]

yes i was typeing when jon posted that.

just trying to find out what kind of amps its pulling and then see if i can find a convertor.

thanks so far

 

[Jon Wildsmith]

the 24v start is a long way from KISS, they got a bit carried away with being clever there I think.

 

[grantw]

the 24v start is a long way from KISS, they got a bit carried away with being clever there I think.

I have wondered how it works ... I guess (with my limited electrical understanding) that there is a huge diode in there somewhere?

 

[Jon Wildsmith]

I have wondered how it works ... I guess (with my limited electrical understanding) that there is a huge diode in there somewhere?

No diode involved, not in the way you mean. The wiring at the change over solenoid is such that normally the batteries are connected in parallel. When the change over solenoid is powered it re-arranges things so that the batteries are in series. You only get 24v when measuring from the positive terminal of the passenger side battery (what the starter is connected to) to the negative terminal of the drivers side battery or bare metal on the car though. The 12v systems are connected to just the drivers side battery so they still only see 12v. That's how the 12/24 works but another twist is that the starter relay (the one just inside the passenger wing) earths via a control unit in the passenger side kick panel that will only connect that earth if it sense 12v on the passenger side battery negative terminal, so the starter solenoid isn't powered until 24v should be available for the starter. So when fault finding 24v start and the starter solenoid isn't getting power from the starter relay check that relay is being earthed as well as checking it has power.

If you look at the connections on the change over solenoid it all makes sense and is quite clever how it's arranged but boy did they over think it!

 

[Bat21]

No diode involved, not in the way you mean. The wiring at the change over solenoid is such that......

Jon, after doing the mod you mention HERE, which battery actually starts the car, the drivers side one or the passenger side one.... or is it essentially both but still in parallel supplying 12v?

I want to do this mod to make things less complex regarding the starting system, but at the same time I want to make sure I understand what's happening.

 

[AndycruiserguyLomas]

I think I know what Stu is trying to achieve but AFAIK you cant have 12V and 24V items running on a vehicle together.

Andy

 

[Jon Wildsmith]

Jon, after doing the mod you mention HERE, which battery actually starts the car, the drivers side one or the passenger side one.... or is it essentially both but still in parallel supplying 12v?

I want to do this mod to make things less complex regarding the starting system, but at the same time I want to make sure I understand what's happening.

If that is all you do then yes both in parallel. For a bit more effort you can make it so the passenger side battery powers the normal 12v circuits inc starter and the drivers side is available to use as an aux which is what I've done.

 

[Bat21]

Ideally that's what I want Jon, it would be good to isolate the DS battery form the rest of the system once switched off.

I already have a split charge system for the 3rd battery, but it would be good to have an additional 'auxiliary' battery.

 

[Iwan]

Thats funny cause I want to run some 12v stuff off my 24v 60 series. If it was low draw equipment off the top battery (+ outlet connected from is 12v) does the 24v earth interferer with this equipment. I want to run a EGT gauge but cant find one in 24v??

I know not to run a 12v winch off the top battery as the other battery will over charge and blow..

 

[AndycruiserguyLomas]

It might work taking the feed from the radio as thats 12v from the dropper or fit a 2nd dropper.

Andy

 

[Chris]

Exactly what I am in the middle of Paul, but I am not having a third battery this time. The driver battery will be the aux to run the fridge etc. This truck is going to be simple but effective. Don't need the extra weight of a third battery. I will post the set up on the build thread for my 80.

I think trying to nab 24v from the batteries to run the compressor could be tricky and does have the potential to mess things up. If you went to 12v start as well, then maybe it would be simpler to consider series connection of the batteries as the starting electrics would be out of the picture. Yiu could then use the redundant 12v/24v change over relay to do that work for you?

 

[Bat21]

Just want to go as simple as possible Chris and do away with (or by pass) as much of the electrickery/wizardry as possible, no 24v needed.

One 12v for starting, and two auxiliary batteries that are isolated from the starter battery once the engine is off.

I have the existing auxiliary battery fed from a split charging device that isolates it once the alternator stops charging. This can be used to also charge the drivers side battery which will become the 2nd auxiliary battery. But Jon says the cars 12v system runs off the drivers side battery, so I'm guessing I need to remove the connections going to it and move them over to the passenger side?

Once the weather improves I'll get out there and have a poke around, maybe it will all become more apparent then.

Not sure what you mean about connecting 2 batteries in series to give 12v, connecting 2 x 12v in series will only ever give 24v.