So.... I've bought a ThermoKing Tripac auxiliary power unit to install in our Gillig. This is a new wrinkle in the conversion plan, and I don't yet have my mind around it. I have some idea of how to proceed with installing the AC and the heat (both backups/supplements for existing systems), but one of the primary uses for this APU will be charging the 490 amp hour battery bank in our solar electric system.
The bus charging/starting system is 24v. So is our house system. The APU comes with a 65 amp, 12v alternator. I need to be able to convert that output to 24v to be able to top our house batteries. What are my interface hardware options?
I want a charger robust enough to handle 65 continuous amps without strain, but I'm also interested in efficiency. I briefly considered replacing the 12v alternator with a 24v model, but I need to charge the 12v battery that will start the APU. Apparently, in most OTR truck installations, APUs are started by the chassis batteries. That's not an option here, even if the bus used 12v. I need a separate starter battery for the APU since it will be operating mostly when the chassis batteries are switched off.
I can think of several ways to approach this, but I'd like opinions. I appreciate your sharing.
Jim
How is your bank made up? 6es 12ves or 24s? If 6 or 12 it can be wired to be charged with the 12 volt system and costs little to do.>>>Dan ( the 12 volt starter battery for the generator can be stand alone)
Battery bank consists of 4 12v 8D AGM batteries. How would that wiring work?
Jim,
So you have *no* use for 12vdc in your coach?
Is the APU's alternator the single source of electricity on the unit?
Ok, well I'm sure you've pondered the several ways this can be done.
In my rig, I'm designing a 48v inverter system so I have a similar issue, but my route might be overly complicated or expensive for what you are doing.
My goal was to get the alternator of the truck to charge 48v. The way I will do this is to use a 12v inverter that outputs 120vac to a 48vdc battery charger.
The inverter will be switched to the ignition key so it doesn't operate when the truck is off.
What I like about this setup is that I get 3 or 4 stage charging of the house batteries vs "dumb" charging from an alternator.
You could do this by using the APU's run signal (there are ways around it if it doesn't have one) to open a relay that switches on the inverter (and subsequently the charger).
There are inverters that have this "switched" provision built in, but it could be done on those that don't using a HD relay directly to the inverters' input.
Option 2 might be to see if there's space to mount a separate 24vdc alternator to charge the house batt's, and have the 12v system only charge the APU battery.
Quote from: Utahclaimjumper on June 29, 2014, 05:51:21 PM
How is your bank made up? 6es 12ves or 24s? If 6 or 12 it can be wired to be charged with the 12 volt system and costs little to do.>>>Dan ( the 12 volt starter battery for the generator can be stand alone)
Yes, please tell us! Ia this a series/parallel configuration? I thought that couldn't be done.
Can you swap out the Alternator? Whats it powering on the APU? Are there 24v parts available? How about a dual powered alternator with 12v and 24v outputs?
Just typing out loud here :)
-Sean
I'd put a 24V alternator on the APU and use a 24V -> 12V converter to charge the little battery for the APU. Make the power output of the APU what you really want and need, and do the conversion for the "small stuff". That is the most efficient way; also, you're only converting a small amount of power, not the largest amount.
Yes, it seems like the 24v alternator is the answer. You can wire one of your 12v batteries or center tap the bank to start the APU. An equalizer can also be used as a 24v to 12v charger. We do that to charge the house bank OTR.
There are equalizers around that can charge a 24 volt battery from 12 volts, they exactly double the input voltage and work fine. They are a little pricey at around $200 and they only handle around 10 amps on the 24v side. I can't find the link I had to where I ordered mine. I am using one as a 24v to 12v converter for my trailer lights but when I wired it up to a trailer that had a battery, the brake lights came on on the bus - it was feeding 24 volts back into the bus system. Here is a bigger brother to the one I have: http://www.cooperindustries.com/content/public/en/bussmann/transportation/products/power_conversion/battery_equalizers/12040x_converterequalizer.html (http://www.cooperindustries.com/content/public/en/bussmann/transportation/products/power_conversion/battery_equalizers/12040x_converterequalizer.html) It would charge the 24V side at up to 40 amps from a 12V source. You can only go as high as 32 amps on the 24v side maxing out your 65 amp 12v alternator, so it would have ample headroom. I don't know how much it costs, probably a bit under $500 from looking at similar sized units.
If you hook up a second alternator to the APU you can float it's ground and use it to charge the 12v to 24v battery of the 24v set, while the regular grounded alternator charges the 0v to 12v battery. As long as you hard-wired it so you couldn't hook it up wrong that would work fine and probably be as cheap and foolproof as anything else.
Brian
Why are youall making this so complicated ?
Lostranger has 4 12 volt batteries and a 12 volt source on the APU which is (or better be) isolated from his coach's 24 volt system. Just run positive and negative directly to the 4 batteries - 2 wires in parallel along with voltage regulation and, if needed, isolation.
edward
Quote from: shelled on June 30, 2014, 11:36:30 PM
Why are youall making this so complicated ?
Lostranger has 4 12 volt batteries and a 12 volt source on the APU which is (or better be) isolated from his coach's 24 volt system. Just run positive and negative directly to the 4 batteries - 2 wires in parallel along with voltage regulation and, if needed, isolation.
edward
This sounds like short to me. While I understand that it is an array of 12v batt's, and each has it's own voltage of 12vdc, once you have them series wired the voltage potential between any battery's negative and another's positive is different.
It seem like you would need 2 totally isolated alternators to do this (or 4 alternators for 48v). It would be slick if someone had an isolator for this purpose, but I'm not quite getting how you can tie either the grounds, nor the positives together in a series wired array?
Maybe need a diagram or am missing something?
I can't see a way to charge a 24v bank from a single 12v source while it's being used to supply 24v loads at the same time, just with wires. Obviously easy to charge the battery bank if it's temporarily reconfigured to a 12v bank, but that's not the ask here. I see either make 24v out of the 12v with a converter, add a second 12v source, or add a 24v source.
Brian
First, all the early posts here were about more and more complicated ways of utilizing the APU to charge a 24 volt battery bank and I am downright allergic to complications - that's what the doctor calls it when something goes wrong.
Second, you cannot charge a battery bank without charging the batteries. The batteries are not 24 volt, they are 4 12 volt batteries wired wired to give 24 volts with 2 batteries in series to make 24 volts and two sets like this wired in parallel to give greater overall capacity. The individual batteries are still 12 volts and if you add a seperate circuit (both pos and neg) from the 12 volt alternator, it will charge the 12 volt batteries just fine.
Brian, if what you say were fact, you would not be able to run 2 standard batteries in parallel because the 12 volt battery is actually 6 x 2 volt batteries built into one case.
Audiomaker, the wiring to do this is not complicated. One wire from the alternator goes to all the battery positive terminals and stops. Another wire goes to all the negative battery terminals and stops. Voltage regulation and isolating elements if/as needed go in the appropriate wire.
I think it is important to look for simple solutions wherever possible. That may not be the case here, but it ought to be considered at least as a thought experiment.
edward
Shelled, what about the fact that in a 24 volt system the 0 - 12v battery has it's positive post connected to the negative post of the 12 - 24v battery? You've just connected your negative to your positive and created a dead short in your charging system. I could say trust me, I've been doing this for 40 years, but I won't. You are missing the point that while the system is charging it is still an operational 24 volt system. Your approach is to just rewire the batteries as a 12 volt parallel bank, and does not satisfy the requirement.
Brian
been watching this: I have very little 24V requirements. wiper & defroster fans.--The truck engine came with a 12V alternator & starter. The ddec is 12 volt. I have 2 series 31's in parallel=12 volt for starter. I then need 24V so I added another 31 battery and achieved 24 volt The starter and 12 volt tap is before the #3 battery which then supplies a 24 volt main. question is how to charge batt #3. The alternator supplies 13.87 V to batteries 1 & 2. Observation: the charge in # 3 is increasing but does not show 13.87 volt--It reads 12.7 up from 12.5 in 20 minutes idle time. The dash gauge shown 27 volt with engine running. all things hooked to either 12v or 24 volt have the correct readings. I forgot there is a 12V master switch also. Comments please--do I need to add a charge system to #3? Bob
It sounds like there is nothing to charge battery #3, if there is you didn't mention it. You need something to charge it, either of the systems that have been discussed here. Since it is essentially half the size of the other pair of batteries whatever you do will probably over-charge it. If you really have very small 24v requirements I would use a voltage converter to create 24v from 12v and have a stand-alone 24v bank - basically add a fourth battery. They need to be the same as each other but they don't need to be group 31's, unless that is easier for you.
Are all your other bus systems converted to 12v, like lights and so on?
Brian
everything except wiper motor and defroster fans is 12 volt. That what I thinking about # 3 charging. I have a vanner 100 amp but have not thought that thru yet(not in system). I have a 4 bank battery charger and it worked out .(On another project-)- 4ea 10amp 12 volt leads(like in bass boat) Guess the light just came on! Trolling motor was 24volt in it.. has 4 each 12 volt batteries. I took wiper motor to re-builder and they wanted $400 to change/duplicate it to 12 Volt plus I would have to replace defroster motors also.. I have no house bank and don't plan on it. Thanks for helping me think this thru.. Charge rate on # 3? would it be effected by charging 1&2 which are hooked up to 12V alt on engine( If separate charge source)..Bob
Quote from: bevans6 on July 01, 2014, 01:31:25 PM
Shelled, what about the fact that in a 24 volt system the 0 - 12v battery has it's positive post connected to the negative post of the 12 - 24v battery? You've just connected your negative to your positive and created a dead short in your charging system. I could say trust me, I've been doing this for 40 years, but I won't. You are missing the point that while the system is charging it is still an operational 24 volt system. Your approach is to just rewire the batteries as a 12 volt parallel bank, and does not satisfy the requirement.
Brian
I must concur, however you could charge from multiple 12v sources in a series array if they were totally isolated.... which is an interesting prospect.
For instance, 4 12v battery chargers (or alternators) could charge a 48v array.
Simply wiring parallel to each battery in a series string would not work, and as described...would make a heck of a short.
Also, having 4 100% isolated 12v alternators (2 for a 24v array), might look cool, but it's impractical.
But what about isolators? I wonder if there is any way to wire a dual battery isolator to do this (actually a pair because you'd need it for the ground too).
Sounds like some sparky fun to find out!
I'll be honest - charging batteries isn't rocket science, all you need to do is figure out the charge rate, how to monitor the charge level ( easy with a modern charger or alternator, they automatically monitor charge level) and then balance the system. I bet the boat guys have this covered - there is probably an off-the-shelf product that does exactly what Audiomaker suggests - multiple independent charging systems from a 12 or 24 volt input. I could easily design and put one together from off the shelf products, but if it isn't productized you are paying retail for all the parts so you pay a lot. The real key would be to have 12v input, 12 volt output (basically passing through the alternator output voltage) but with all the outputs having floating grounds so they can be connected to individual batteries without worrying about shorts, and each having independant smart charger capability built in to control the charge rate for each battery.
Here is an easy way to go. Get a cheap 1000 watt pure sine inverter, two 12 volt 20 amp smart chargers, run the inverter from the APU (or bus) alternator and connect one charger to the 0 - 12v set and one charger to the 12 - 24 volt set. Total cost under $250 bucks. Robert, you could do that and cut it in half, all you need to do is charge the 12 - 24 volt single group 31 you have. A little inverter that is powered by the 12v start batteries (and the bus alternator when running), a small smart charger and a switch to control it so you aren't charging the battery when the engine is off. A 20 amp smart charger draws around 300 watts from an inverter, you do want a pure sine inverter to run the charger though. It's counter-intuitive to use an inverter to power a battery charger but in the context of powering from an APU or bus alternator, it makes a lot of sense.
Brian
Glad I asked. Thanks for all suggestions. I especially love background explanations.
Still pondering this one. We have some need for 12v in bus (CB, cable modem, cell phone chargers), but we use a step down. I was leaning toward changing to a 24v alternator and charging APU starter battery with a step down converter and isolator. The complication with this approach is that the APU brain and systems work on 12v. This includes engine fan, condenser fan and evaporator fans. Our 12v need will be larger than before. Guess I'll have to keep the 12v alternator.
I'm still in the process of harvesting the APU and its systems from a wrecked tractor. Soon as I can get home, I'll look into the possibility of adding a second (24v) alternator. I'd like the idea of having an alternator dedicated to charging the main bank.
Someone on the thread asked if the APU will be the only means of charging the main battery bank. Our primary charging source is solar.
Jim
Brian, your post came up while I was typing. I'll read it slowly later today when I can think about it. Thanks for chiming in.
Jim
Quote from: bevans6 on July 02, 2014, 03:59:16 AM
I'll be honest - charging batteries isn't rocket science, all you need to do is figure out the charge rate, how to monitor the charge level ( easy with a modern charger or alternator, they automatically monitor charge level) and then balance the system. I bet the boat guys have this covered - there is probably an off-the-shelf product that does exactly what Audiomaker suggests - multiple independent charging systems from a 12 or 24 volt input. I could easily design and put one together from off the shelf products, but if it isn't productized you are paying retail for all the parts so you pay a lot. The real key would be to have 12v input, 12 volt output (basically passing through the alternator output voltage) but with all the outputs having floating grounds so they can be connected to individual batteries without worrying about shorts, and each having independant smart charger capability built in to control the charge rate for each battery.
Here is an easy way to go. Get a cheap 1000 watt pure sine inverter, two 12 volt 20 amp smart chargers, run the inverter from the APU (or bus) alternator and connect one charger to the 0 - 12v set and one charger to the 12 - 24 volt set. Total cost under $250 bucks. Robert, you could do that and cut it in half, all you need to do is charge the 12 - 24 volt single group 31 you have. A little inverter that is powered by the 12v start batteries (and the bus alternator when running), a small smart charger and a switch to control it so you aren't charging the battery when the engine is off. A 20 amp smart charger draws around 300 watts from an inverter, you do want a pure sine inverter to run the charger though. It's counter-intuitive to use an inverter to power a battery charger but in the context of powering from an APU or bus alternator, it makes a lot of sense.
Brian
That's pretty similar to what I posted on the 1st page of this thread... just go from the 12v APU battery to an inverter in the 1500w range (sine), and then to a charger (just use a single 24v smart charger).
The Xantrex ProWatt SW is sine wave, and can be turned on and off by 12v+, so you use the run signal of the APU to switch it on.
The inverter runs only when the APU is running...the charging is "smart", and you get an extra inverter circuit to anything you might like to power only while the APU is running. (and a 12vdc battery source as well instead of tapping the 24v array).
The downside is you lose a little efficiency in the conversions so your cost per amp hour goes up maybe 20%, but if it's a secondary system to solar and also used for heat and A/C mechanically, then the efficiency increases on that side more than make up for it.
Sean
Brian,
Thanks for sharing, you have added a lot to my understanding.
You mentioned a theoretical system that would wrap all this up in one unit. My nephew works for a rural wireless ISP and they use a controller for their solar power systems that sounds like it provides individual charging control for multiple non-identical batteries and multiple voltage outputs from multiple DC and AC inputs. I'm hoping to get a look at this when I get a chance to visit him later this summer. Knowing how cost conscious these folks are, I'm also hoping it's affordably priced.
edward
And, as a total aside from this but I hope it's helpful, a friend of mine has a bus charter company and if he has a hard-starter, he takes an ordinary 12V "jump box" (the plug in type that looks kind of like a briefcase with jumper cables coming out of it) and attaches it to one of the 12V batteries in a 24V pair. It's amazing how a just-barely-turning-over engine without will suddenly jump into life when that single box is added. I might not work *all* the time but it is amazing when it does, which seems to be usually.
Hey Guys:Don't know if this will be any help or not,but my Prevost has a 12/24v system.It has six house battery's and 24v and a 12v that they refer to as "isolators"?.This whole system is charged off a, as far as I can tell, a 12v alternator.A very large one!Some of the guy's on the Prevost web site can probably shed more light on this than I can.On the Prevost, this is a can of worms as you never know which voltage you are dealing with until you check it with a volt meter!
Bigred: red wires are 24 volt and yellow 12volt on prevost wiring. # tatoo on wire will give you what they are for. prevostcar.com under wiring diagram gives you the code. Bob