24v to 12v Step down converters, what is 12v really?

[neoneddy]

When I initially built our bus conversion, I tried to save where I could.  This lead to numerous times I ended up buying items twice, can I get a witness?  I initially went with a cheap Chinese no name 24-12v converter.

Anyway, I was noticing my diesel air heater was giving me some white smoke during full fuel situations.  So I did some thinking, it could be that there is some soot in the burn chamber (still could be the case) but also could it not be from not getting enough air?  I noticed under full load it was only getting 11.3v or less with the glow plug on.  I measured my 24-12v converter and it was non adjustable and outputting 12.3v  Not surprising that by the time it went through all the wires, connections, fuse panels, etc I'd get a volt of drop.  So I'm thinking, if I can get more volts, I'll get more fan speed, more air, less smoke.

I bit the bullet and bought a Victron Orion 24-12v converter last week and installed it yesterday.  I set the voltage to around 13.8, I figure most things work better with traditional alternator output voltage.  So far no real difference in the diesel performance, smoking hasn't been an issue with the warmer temps, but we're getting into -20f range here soon, so we'll see.

I also had a 12v to USB converter die on me this last fall,  it powered my raspberry pi with a LCD screen for my Victron monitor, I suspect I was pushing it to it's limit.  I wonder if the lower volts was harming that.  I'm also hoping the extra volts will help my 21' awning roll up  better.

So curious what everyone's take is on what actual voltage do you run your 12v house voltage at?

[richard5933]

I've run across this problem a few times, most recently when installing a bank of four converters to run my 12v headlights on a 24v bus.

You are correct - nearly all automotive appliances and devices intended for use on a 12v system are configured for optimal performance at about 13.8v, which is typical for an auto alternator when the vehicle is in operation. That's the voltage I've been using for my converters on the headlights and finally have good light output.

On most S&S (sticks and staples) RVs, they are also set up for use when the converter or charger is running which is somewhere between 13.2v and about 14.0v. A fully charged 12v battery will likely measure about 12.7, and by the time it's down to 12.0v it's usually down to about 50% SOC (state of charge) and in need of recharge.

I'd stick with the 13.8v converters, and make sure that the one you use can supply more than the anticipated current draw on them. I usually go with double the needed capacity to ensure that they run cooler, on the thought that cooler operation results in longer life. Push converters towards their max output and things start to fail sooner.

[neoneddy]

This one is 70 amps.. nearly double of what my last one was, I bet that helps too.

[richard5933]

In addition to bigger, I also like redundancy. My headlights are power from the factory with 4 separate circuits - one for each side hi beam and one for each side lo beam. I kept that redundancy and installed four separate 24v-to-13.8v converters so at most I'd lose one of the four and not all four. These replaced the OEM resistor bank which was failing.

I never like to put all my eggs in one basket, or in this case in one converter.

[belfert]

My inverter is 24 volts so my battery bank is 24 volts of course.  Some stuff I can't get in 24 volts so I tap the battery bank to get 12 volts with a Vanner Equalizer keeping the two halves of the battery bank in balance. 

My 12 volts is half of whatever the 24 volt battery bank is sitting at.  I am usually a bit under 13 volts unless the charger is providing power when it will be closer to 13.5 volts.

[Jim Blackwood]

Modern alternators have a sense wire that goes to the battery. That way they don't measure the voltage from the alternator charge which is always a little higher than at the battery due to the resistance in the wire, and then you also have the resistance in the sense wire. It isn't that much but a couple tenths of a volt can make a big difference.

Electrical/electronic components that are made to hold up to 12v are not going to fail on 24v, although that's not true with lights and less certain with motors. It always depends on how well they can get rid of the extra heat. So when it's cold out I can't see there being much of a problem running that Webasto on 24v even when it is supposed to take 12v.

I remember when we did 6v to 12v conversions and all we did was change out the incandescent bulbs. Starter and wiper motors did fine.

Jim

[neoneddy]

Electrical/electronic components that are made to hold up to 12v are not going to fail on 24v, although that's not true with lights and less certain with motors.

So true, this summer I was working on my old onan generator.  I was experimenting with using chassis ground and part of my 24v battery bank to start it.  Well wouldn't ya know it, once time I connected it to the 24v side.  That thing startup so quick I was amazed!   I seriously contemplated on leaving it on 24v.

So far so good the diesel air heater is working better than ever.  Only hit 12.5v during startup this morning.

[Ed Hackenbruch]

If i remember right, 12.2 is at 50% charge and 12.0 is at 25% charge.....for optimum battery life don't let them get below 50%.  This is for lead/acid batteries, don't know what it is for other types.

[neoneddy]

Right, this is about a step down converter and what voltage it was putting out.  I have a 24v battery bank, so my 12v side is consistent no matter what.  Before I couldn't control it, it was always 12.3   Now I can set it anywhere from 10 to 15v , I chose 13.8 for now.

[richard5933]

My Yaesu ham radio gear runs on 12v, but of course they don't recommend that you actually use 12v. The recommended voltage is 13.6v - 13.8v, which is what I have used in the bus for the 12v systems as well.

[fortyniner]

Did you say -20F!!!  What kind of diesel heater is that? 

[richard5933]

Did you say -20F!!!  What kind of diesel heater is that?

You must not be from the upper midwest. We're expected similar weather here in Wisconsin this weekend. Not quite as cold, but still down around -10F. I spent about 3 hours out in 0F this morning clearing snow. It wasn't all that bad being dressed appropriately.

[dtcerrato]

We live in Florida & just gave best offers on two Chinese diesel air heaters on eBay for when the bus is in the cold. We'll see...

[windtrader]

Just curious what the story is for those suffering below freezing conditions. How many buses are being used or they all winterized and parked?
What experience can be shared by those who have ventured out in freezing conditions and gone boondocking? What are the key issues to ensure a happy winter bookdock expedition?
With all the snow up in the Sierras I may be simply stupid but thinking from this warm room that it might be pretty exciting to take the bus up the hill for a few days.

[luvrbus]

People working on heaters for -20* and I am thinking about checking my dash air to see what is wrong you guys are tough