Nps second alternator

[Cuddy]

Hi, has any one fitted a second 12v alternator to there Isuzu? I am currently setting up a 2013 nps crew cab for a trip around oz. We will be towing a caravan with a 100ah battery and an absorption fridge that I will want to run from the vehicle when driving. I will have a 12v 165ah battery fitted on the truck to run my 12v evacool fridge and lights etc.
The Isuzu is 24v with a 80 amp alternator. I have some concerns that I may overload the trucks alternator if I run everything off it.
I was planning on using 2 redarc bcdc 25 amp chargers. One on the truck and one in the caravan. The caravan fridge has a big amp draw of 14 amps. If everything is running - fridge in van drawing 14 amps and the 2 chargers (25amp each) I will be drawing 64 amps off the alternator . I don't know what the truck draws to run but I am assuming around 40 amps with everything running, which is obviously more than the alternators output.....

Sooo this has lead me to the second alternator. I know it has been done before and was hoping someone may be able to point me in the direction of a bracket and suggestion of what alternator to use. Any photos of one setup would be great.

Cheers- Brent

 

[Aussie Iron]

Why wouldn't you run the fridges on 24v. Less current draw. You could also upgrade your alternator to a higher output. Lot less trouble. Redarc also make step down transformers to run your fridges if 12v on 24v system.

Welcome to the forum,
Dan.

 

[gait]

I'm a bit confused about what is 12v and what is 24v.

Maybe work in watts = volts x amps

So 10 amps at 12 volts is same as 5 amps at 24 volts.

Are the Redarc amps at 24v or 12v (input or output)?

The diesel requires little to run. Lights take a bit. eg 2 x 60w headlights = 5 amps at 24v or 10 amps at 12v.

I have a sneaking suspicion the existing 24v alternator may have more than sufficient power.

IIRC the alternator has a serpentine (non-slip) rather than vee belt.

Provide large enough cable to caravan to avoid too big voltage drop.

The absorption fridge is a bit thirsty on 12v. 6 amps for a small Waeco.

 

[Cuddy]

Hi Dan, All my gear is 12 volt so wanted to keep the system the same. 24- 12 reducers seem to be inefficient way to convert the power plus a decent redarc one is the same price as the bcdc charger. I am looking into a bigger alternator also but it needs to have a vacuum pump fitted also which might make things a bit harder.
Thanks for the welcome, the forum has been a fantastic source of info.
Brent

 

[steve66]

Hi Brent,

Rapid Power is Brisbane make an upgraded alt for Isuzu's, has vacuum pump mount, look at their RP3 model, top shelf quality but not cheap, around $2k last time I asked.

Instead of voltage reducers look at a voltage equaliser, redarc makes these as well, allows you to take 12v from a 24v bank, I have a 2nd hand one if you are interested.

Cheers Steve

 

[Cuddy]

Hi Brent,

Rapid Power is Brisbane make an upgraded alt for Isuzu's, has vacuum pump mount, look at their RP3 model, top shelf quality but not cheap, around $2k last time I asked.

Instead of voltage reducers look at a voltage equaliser, redarc makes these as well, allows you to take 12v from a 24v bank, I have a 2nd hand one if you are interested.

Cheers Steve

Hi Steve,

Thanks for the info. Wow that is certainly not cheap. I have spoken to redarc Tech several times and we discussed an equaliser. Seems that for the money and the result i require (charging the van battery) that the BCDC is the way to go. After reading Gaits comments above i realised some of my allowances\comments are incorrect. As he mentioned the input of the BCDC chargers is 24v, so it is not drawing 25 amps at 24v more like 15 amps (Allowing for some inefficiency). The fridge in the van will be drawing off the van battery when the vehicle is running, its power is coming out of the second BCDC that is in the van so I wont need to add the fridge amp draw into the sums.
This means i will be drawing closer to 30 amps to run the charging system. I am now thinking that the original alternator will be sufficient.As Gait again mentioned.

I was hoping to try and put a multi meter on the truck with everything running to see if I could get an idea of the amp draw on the alternator, just for piece of mind.

I assume I would not be the first person who may have had a setup like this- perhaps I am looking into it too much??

After saying all of this......I was planning on running 6B&S cable to the van via a 50 amp anderson plug. The cable will have a 40 amp midi fuse at the at both ends of the cable on the truck. This will feed the BCDC charger 24v which is then reduced to 12v to charge the battery. I am planning on using a 24v relay with a wire from the ignition to switch the relay on only when the truck is running- this will control the power to the fridge. I only want the fridge running when the truck is because of the big current draw. Any extended stops with the van connected I will switch over to gas.

Any comments or advice by forum members is greatly appreciated.

Cheers Brent

 

[SkiFreak]

Like Gait, I think you should be working is Watts, rather than Amps, when doing your calculations. This takes the whole 12/24 volt confusion out of the equation. But not everyone thinks that way.

Putting that aside for a moment... will you be drawing 30 Amps @ 24v or 12v?
Assuming that it is 30 Amps @ 24v and you have a cable run of 10 metres (maybe more), if you use 6B&S cable you will have a voltage drop of about 3.5% (0.84v/25.2 Watts @ 25 degrees Celsius).
Ideally you would have less than a 2% voltage drop. Throw in the efficiency losses of the BCDC and you may not be getting the current at the caravan battery that you might expect.

-------------------------------
Edit

If the truck is running then you should have an alternator voltage closer to 27.6v which would give you a 2.96% voltage drop with 10 metres of 6B&S cable @ 30 Amps.

 

[gait]

reasonably common setup among the caravaners,

6 B&S is about the norm. Some run a second cable for the fridge when 12v to 12v. Not feasible/necessary with 24v.

My maths is different to Owen's. 15A @27.5v for 10m (each way) leaves 27.1v to the Redarc.

24v is much better than 12v. Voltage drop is a function of the square of the amps.

Check what your fridge needs.

Most consumer multimeters only read up to 10A and need to be in series (mess about with disconnecting wires). Useful meter is a DC clamp meter. I have one of these. Very useful when things go wrong. Cheaper but slower from overseas. Not all clamp meters are DC.
http://www.ebay.com.au/itm/UNI-T-UT...131867?hash=item4d5944539b:g:voMAAOSw8HBZEGBq

 

[SkiFreak]

reasonably common setup among the caravaners,

That doesn't necessarily make it a good setup.

 

[gait]

That doesn't necessarily make it a good setup.

haha. Just that it works. I recall when I first started messing with this stuff. Several years of arguments until someone added a second cable for the fridge with 12v to 12v. Still much discussion about the need for DC-DC conversion, usually relating to "smart alternators". I needed 12v-12v charger because alternator on old bus only reached 13.7v. Things sort of evolve.

24v to 12v is not common among the vanners but its very much "easier".

 

[steve66]

Hi Brent, Understand your issue now, as Julian says- lots of info on the caravaners forum about the ways to do this, has been done to death. DC-DC charger seems a common solution. I've had to use converters for my 12v stuff as Redarc advised the voltage equaliser is not suitable to use with Lithium's.

Julian, thanks for the link, I've been looking for a good DC clamp meter, yours has 40a min range listed, have you found that it's works at lower currents?

Cheers Steve

 

[Family Friendly 4x4]

Busy doing the same thing

I am about to install a second alternator (120 Amp) in order to charge my 6x 12v deep cycle batteries on the FG84 whilst on the move.

The only challenge I understand is finding space for such a large alternator, they normally fit 100 Amp alternators to trucks or so I am told.

I am having the add-on alternator installed by a truck refrigeration specialist who makes up the engine mount etc it is something they do on a daily basis.

I could obtain some details and a photo once installed but can suggest that you speak to a supplier of truck refrigeration units as these trucks are often fitted with a second alternator.

 

[gait]

..

Julian, thanks for the link, I've been looking for a good DC clamp meter, yours has 40a min range listed, have you found that it's works at lower currents?

Cheers Steve

I've had it detect down to a hundred mA though wouldn't vouch for accuracy.

 

[steve66]

Thanks Julian, for $50 I'll give it a crack. The fluke ones I've being eyeballing are heaps more than that.

 

[SkiFreak]

You might also want to consider something like the Victron Orion 24/12-70A DC-DC converter, which is under $300.