dual or 3 alternators

Greetings to All.. This is my first post here but I am not new to this sort of thing, just never done what I am wanting to do and hoping I can get some guidance from someone that has experience with this. As you might guess by my username I drive a truck for a living. I just purchased a new (to me truck)that is equipped with an APU. What is an APU you ask? It is an assembly of parts that is designed to provide heat, A/C and 110v to the cab/sleeper of a truck so that the driver does not have to run the truck engine all night to eat/sleep/whatever.. They normally run on a small diesel engine that burns about 25% of the fuel that the big motor uses per hour. They are pretty expensive normally running from $6,000 to almost $12,000 installed. So anyway... my APU is no longer made. The company went out of business a few years ago and some (most)of the parts are no longer available. The engine part runs just fine and it is a brand/model that is used in many current APUs so parts for it are no problem. The issue is the generator section of the unit. It is supposed to put out 6kw of 110volt AC. It does not. "IF" I am able to find a power head to replace the DOA one it will run about $2,000. I am looking to find a more economical way to get the rest of the system operational until I can afford to replace the entire thing with a new APU. What I am thinking about doing is using the good diesel engine to power 2 or 3 165a alternators that I can get new for about $200 each. I already have an inverter sufficiently large to run what I need to run, I just need a way to power it and keep the batteries charged. Physically installing the alternators should not be a problem. My issue is how to properly wire them so that they will work in unison to provide the needed amperage in a happy, harmonious way. I have done some searching here (And on other sites) and have read about alternators fighting each other if not wired correctly. I know for a fact it can be done and done properly with at least 2 alts. Ford (And perhaps others) offer dual alts from the factory on their diesel trucks. I have seen pictures of some of the audio competition rigs some guys build with 5 or more alts. The APU will be run for about 10-12 hours per day, 5-6 days a week. It needs to be ultra reliable. I can not be having to repair it every week. It needs to last so it needs to be done right. All alternator power will be going into a single bank of 3 truck batteries. (This is the normal configuration for large trucks) So, the question is, how to do it right? NOTE: An additional question is what happens when I have both the APU and the truck engine running at the same time? I have researched pretty much all possible options to doing this and have arrived at this as most likely the best way to get to the desired end result. This does not mean that I am not open to suggestions of other ways to get it done but most likely I have considered and researched it and for 1 or more reasons it is not as good of a solution as this may turn out to be. I appreciate any help in this and will be happy to answer any relevant questions and or provide any needed but missing information to help work out the wiring solution. Thanks in advance!

It seems that paralleling alternators is not a big issue, I'd merely suggest that they be matched (same model & capacity). PS - I'd stay away from Bosch and other alternators that are damaged after jump starts etc. PS #2 - it doesn't hurt to have long (and identical) cables from each alternator to their common join point. Not that it may make much difference being low-Ohmage cable, but paralleled voltage sources are often joined using resistors to help ensue current sharing (unless sources are designed to be paralleled - eg, same voltage regulator & active current sharing). Re the AC, could you run an AC generator instead? Powering heavy AC loads from 12V or 24V inverters isn't as efficient and usually requires heftier batteries. With engine & APU at the same time, any interconnecting power sources must be isolated unless configured for sharing.

oldspark wrote: It seems that paralleling alternators is not a big issue, I'd merely suggest that they be matched (same model & capacity). PS - I'd stay away from Bosch and other alternators that are damaged after jump starts etc. PS #2 - it doesn't hurt to have long (and identical) cables from each alternator to their common join point. Not that it may make much difference being low-Ohmage cable, but paralleled voltage sources are often joined using resistors to help ensue current sharing (unless sources are designed to be paralleled - eg, same voltage regulator & active current sharing). Re the AC, could you run an AC generator instead? Powering heavy AC loads from 12V or 24V inverters isn't as efficient and usually requires heftier batteries. With engine & APU at the same time, any interconnecting power sources must be isolated unless configured for sharing.

THANK YOU for the response!! A few questions/responses for you.... When you say parallel install of alts are you meaning... use the normal alt chassis ground the hot wire from both (Same size/length) go to the battery +? (That being the case, I'm assuming I could use 2 short same size/length cable from the alts to a junction and a single cable from the junction to the +?) Yes, planning on using 2 (or 3) new same make/model alts with same size pulley for a matched set. Talk to me about this AC generator idea... The APU currently has a 6kw DOA AC generator. (The next to impossible to find $1,800 if you do find it part). It is direct coupled to the back of the APU diesel engine. I plan to remove it and in it's place mount a pulley to run the alternators. I had considered raping a gas powered portable 6.5kw AC generator for it's powerhead and figuring out a way to connect it to the diesel engine. However... I know nothing at all about regulating/controlling the 110 it would make. This is why I was going to just go with something I know(12vdc alternators charging batteries that run an inverter). I know there is going to be loss and inefficiency in that system but i'm much more confident that I can make it work. I do agree that building it back as a 110vac system would likely be better but I do not have the electrical engineering / portable generator repair background I need to make it function. It did occur to me to strip ALL the generator components form the portable generator and instead of using the outlets they provided install a junction box and use that as a point to hardwire in the current APU supply to the truck wires. My first question about doing that though is don't I need to be able to regulate the diesel engine RPM somehow? I believe the current gas engine is regulated by the control box for the AC generator. I also think the gas generator is designed to turn at a higher RPM than the diesel engine normally runs at. I suppose I could accommodate that with proper pulley sizing through. Any help/guidance would be GREATLY appreciated.

Common to a single point - usually some "common" point - ie, usually not a battery terminal; maybe a main fuse/rely box; usually a point of your choosing and construction - depending perhaps on what the main load will be. And keep in mind, the alternator(s) could blow if not suitable for paralleling tho it has been years since I've heard of that (not that I've searched, but I have seen lots of parallel alternator pics without negative reports). I presume they won't be single wire aka D+ types but will have a separate "Sense" = S connection in addition to the usual D+ aka L = charge-Light? AC generators usually operate at fixed RPM. 1500RPM is common here (50Hz; it would be 1800RPM in 60Hz stateside) or close to that if motor slip is involved, but other "50Hz time number of poles" versions exist (eg 3000RPM).    Voltage-wise they should be self regulating - not unlike car alternators where the voltage-regulator fed rotor current regulates the output voltage (and thus current supply) to the load. The speed is separately regulated to provide constant speed - it's a mere RPM control - and that is specific to each driver (diesel or gas engine, or motor) and their injectors or carbies etc. The driver has to be capable of providing the required torque - eg, 6kW @ 3000PRM = ~14Nm plus inefficiencies & overhead. A DIY engine-alternator should only require driver (prime mover) matching to the alternator assuming each do their own regulation, ie speed & voltage respectively. IMO diesels are attractive provided glazing from underloading isn't an issue. You should be able to find some suitable genset... 2.5kW units can be obtained for $400 here (they usually sell for $800 to $2500) - I bought a used eBay Chonda {branded Carol) 2.5kVA petrol (stateside gas, but NOT LPG etc!) genny with starter (pushbutton) for $220. [It was for an electric chainsaw. I was considering an inverter and battery(s) but soon came back to my senses. The genny is now a general supply (camping {as if! As if I'd bring a generator camping!} or during local outages. I got a gas petrol chainsaw later (LOL).] Hooking up to gensets isn't an issue if you simply use AC plugs etc. Doing your own AC wiring may require a licensed or approved installer tho in some places Licensing does/did not apply to AC generators/sources that are/were NOT connected to the grid (commercial supply etc). However more international jurisdictions are agreeing, if someone does AC wiring and it is not in principle done iaw local AC requirements AND something does goes wrong, may they pray to whatever deity they mistakenly think will help. I'd certainly look at the genset option UNLESS the AC loads aren't that big in which case ditch the APU and use inverter(s) instead. But for >1500W, or maybe even 1kW (longterm), I'd prefer the genset as a technical solution - it's subject to other issues like noise & fuel. As a bonus, it's an independent power source. You can recharge your own flat cranking battery. If you do make your own, consider an APU replacement. Is there a market out there, or would others appreciate your DIY details? It might simply be a 6kW or 10kW portable genset but with extended controls (cabin on-off switch or timer) which so confuse people yet they can so easily do (if not understand) given reasonable instructions. IMO the DOA is an essential, but technology & times change. If that's the reason the APU company went out of business, oh well, its the DIY forums... or maybe a backyard cottage...? If using the alternator scheme I guess you'd want to run it off the truck engine in preference to any separate motor. Probably a simple changeover switch (to switch relays?) so you can leave it on or off during short stops etc. (But is that extra alts on the truck engine AND alternators driven by a separate engine? Nah - we didn't go there... ) Using the AC alternator... Well over 2 years out in the weather and by $220 2.5kVA eBay Chonda engine still hasn't seized, but when if it does I was thinking of driving it with my vehicle engine (or maybe a solar-charged motor for typical inductive pure-sinewave "inverter" (AC genny) AC output). But that requires the engine to be at the alternator's RPM - eg, 3000RPM without gearing. That should be easy to do with modern EFIs (set RPM or throttle signal) and can still be done with carby systems. There are AC alternators that provide constant output frequency irrespective of shaft speed. These days they use "inverters" (eg, rectify AC to DC and invert to fixed a frequency AC), but in contrast, who cares these days if the frequency varies [warning: motors? aircons? And clocks (LOL)]? And beware AC generator AVRs (Automatic Voltage Regulation etc) or features that cut the supply if frequency varies my more than 5% or 10% etc.

My responses are "buried" in your very informative reply. Look for #### at the beginning of the line to find my response/question..

oldspark wrote: Common to a single point - usually some "common" point - ie, usually not a battery terminal; maybe a main fuse/rely box; usually a point of your choosing and construction - depending perhaps on what the main load will be. ########### Understood. And keep in mind, the alternator(s) could blow if not suitable for paralleling tho it has been years since I've heard of that (not that I've searched, but I have seen lots of parallel alternator pics without negative reports). I presume they won't be single wire aka D+ types but will have a separate "Sense" = S connection in addition to the usual D+ aka L = charge-Light? # ####### Actually I was thinking of using the single wire type for simplicity sake. Apparently you see an issue with that? Assuming I go with the separate wire type like you mentioned, could install a light for each unit on the charge (L)to show if each individual unit was charging? Or would that only work with diode separation in the charge wire for each unit? Don't want to do that because of the voltage drop of installing diodes. AC generators usually operate at fixed RPM. #### That's what I always thought 1500RPM is common here (50Hz; it would be 1800RPM in 60Hz stateside) or close to that if motor slip is involved, but other "50Hz time number of poles" versions exist (eg 3000RPM). ###### Where are you located? (Yes, we use 60Hz.... LOL...) Voltage-wise they should be self regulating - not unlike car alternators where the voltage-regulator fed rotor current regulates the output voltage (and thus current supply) to the load. # ####### Now that you say that I seem to remember something about that. I think the voltage is constant (and regulated) and the Hz is controlled by the speed at which the alt is turned by the motor. The speed is separately regulated to provide constant speed - it's a mere RPM control - and that is specific to each driver (diesel or gas engine, or motor) and their injectors or carbies etc. # ###### On the gas generators I have messed with there has been a linkage attached to the throttle of the prime mover. When power needs rise the linkage is pulled thus speeding up the engine. However... It may be the case that the RPM stays the same, it is simply giving more throttle to provide the additional torque to keep the output RPM the same as at low load. Because the linkage moves and the thing makes more noise I just assumed it was turning faster. Quite possible I could have been wrong about this all along. I never put a tachometer on one to see... The driver has to be capable of providing the required torque - eg, 6kW @ 3000PRM = ~14Nm plus inefficiencies & overhead. ###### Understood. A DIY engine-alternator should only require driver (prime mover) matching to the alternator assuming each do their own regulation, ie speed & voltage respectively. ### The APU prime mover is sized to run a 6kw alternator unit. The alt is currently nonfunctional but (As noted in initial post) the prime mover runs just fine. I have to assume that if the PM is sufficient to turn the factory alt is is good to turn what I need it to now...filling a gas (petrol) generator every day is a lot of extra work when the truck is far to large to maneuver at the gas pump and would have to be hand carried in portable containers IMO diesels are attractive provided glazing from underloading isn't an issue. # ##### The APU PM is diesel. That is the primary reason I want to keep it instead of replacing with a portable generator strapped onto the frame of the truck. A suitable diesel genset is $5k+. Having to keep a gasoline generator fueled every day with a vehicle far to large to maneuver to the gas pump means I would have to shlep portable containers back and forth from the diesel side where the truck is to the other side of the building where the gas pumps are. And I do not ever pay at the pump (To much risk of falling victim to fraud) so I would have to wait in line to pay twice. That just ain't gonna happen... You should be able to find some suitable genset... 2.5kW units can be obtained for $400 here (they usually sell for $800 to $2500) - I bought a used eBay Chonda {branded Carol) 2.5kVA petrol (stateside gas, but NOT LPG etc!) genny with starter (pushbutton) for $220. [It was for an electric chainsaw. I was considering an inverter and battery(s) but soon came back to my senses. The genny is now a general supply (camping {as if! As if I'd bring a generator camping!} or during local outages. I got a gas petrol chainsaw later (LOL).] # ######## I have a donner gasoline generator with a 6.4kw rating. (As with most of these units that rating is likely overstated)It currently runs and makes 110 but would be worth sacrificing to the project. And the PM of the gas unit would still be available for some other project later... Hooking up to gensets isn't an issue if you simply use AC plugs etc. Doing your own AC wiring may require a licensed or approved installer tho in some places Licensing does/did not apply to AC generators/sources that are/were NOT connected to the grid (commercial supply etc). However more international jurisdictions are agreeing, if someone does AC wiring and it is not in principle done iaw local AC requirements AND something does goes wrong, may they pray to whatever deity they mistakenly think will help. # ###### I'm ok with this aspect of the "Conversion"... lol. I'd certainly look at the genset option UNLESS the AC loads aren't that big in which case ditch the APU and use inverter(s) instead. But for >1500W, or maybe even 1kW (longterm), I'd prefer the genset as a technical solution - it's subject to other issues like noise & fuel. As a bonus, it's an independent power source. You can recharge your own flat cranking battery. If you do make your own, consider an APU replacement. Is there a market out there, or would others appreciate your DIY details? # ##### I'm not sure I understand you here. Are you saying to consider perfecting my "Conversion" and then taking it to market? If so, I don't think that is feasible because every APU is different and it seems that there are not that many of this particular type around anymore. It might simply be a 6kW or 10kW portable genset but with extended controls (cabin on-off switch or timer) which so confuse people yet they can so easily do (if not understand) given reasonable instructions. IMO the DOA is an essential, but technology & times change. If that's the reason the APU company went out of business, oh well, its the DIY forums... or maybe a backyard cottage...? If using the alternator scheme I guess you'd want to run it off the truck engine in preference to any separate motor. Probably a simple changeover switch (to switch relays?) so you can leave it on or off during short stops etc. (But is that extra alts on the truck engine AND alternators driven by a separate engine? Nah - we didn't go there... ) # ####### I was thinking of using the APU PM to run the alts. I DO NOT want to use the big engine on the truck for 3 reasons.. 1) fuel economy. The APY engine burns 25% as much as the big motor 2) Wear/tear/hours put on the big engine. 3) More and more there are anti idling laws preventing you from running the big engine. Thoughts?? THANKS..!!!!! Using the AC alternator... Well over 2 years out in the weather and by $220 2.5kVA eBay Chonda engine still hasn't seized, but when if it does I was thinking of driving it with my vehicle engine (or maybe a solar-charged motor for typical inductive pure-sinewave "inverter" (AC genny) AC output). But that requires the engine to be at the alternator's RPM - eg, 3000RPM without gearing. That should be easy to do with modern EFIs (set RPM or throttle signal) and can still be done with carby systems. There are AC alternators that provide constant output frequency irrespective of shaft speed. These days they use "inverters" (eg, rectify AC to DC and invert to fixed a frequency AC), but in contrast, who cares these days if the frequency varies [warning: motors? aircons? And clocks (LOL)]? And beware AC generator AVRs (Automatic Voltage Regulation etc) or features that cut the supply if frequency varies my more than 5% or 10% etc.

"Actually I was thinking of using the single wire type for simplicity sake ". It's not much simpler... The D+/L is circuit is the trickiest - each might each need its own charge light (... or resistor) whereas the S (battery voltage Sense) simply connects to its battery's +12V. Sensing lines rarely consume >20mA. IMO the extra S wire per alternator is a HUGE benefit with minor "extra". But my BIG reason for always using 2 wire etc alternators is that the alternator will give the battery its correct voltage (say 14.2V - 14.4V) even if this means 14.9V at its B+ output because of some 0.5V drop somewhere... Also S-types can easily produce higher output voltages - insert a Schottky diode for ~0.3V or a normal silicon diode for a ~0.6V increase in alternator output voltage. That could be handy for for battery maintenance - ie, equalisation; reversal of discharge sulfates - of maybe some 15.6V AGM charging...? A single wire D+ alternator uses its B+ terminal voltage for its regulation irrespective of what the battery voltage is. And its connection is usually internal hence making diode insertion or extension to battery +12V relatively unattractive or difficult.     Re the charge light OR-ing into a single light via diodes, the diode voltage drop should be irrelevant (lamps & LEDs are still functioning within specs). Two series diodes are not uncommon in older vehicles with firstgen IGN-On warning-light bulb testing.    The alternator's charge-lamp terminal usually only GROUNDs loads of up to an Amp or two, and the charge-lamp's bulb voltage has no impact on the alternator's regulated voltage. Charge lights may need to be less than a certain resistance to initially power the regulator or provide a tickle or trickle rotor current to ensure power generation initiates) but not low enough to overload the regulator's D+/chargeLamp circuit. [These can usually be thought of as an SPDT relay or changeover switch - the chargelight is at alternator +12V and hence unlit when charging else grounded (and lamp on) if not charging. You don't want to short +12V or GND thru it, nor involve more current than they can handle.] Aside from adding current sensing and more cost and complexity, each alternator's charge lamp is probably the best indication of operation. Some sense internal faults whilst others seem happy if the alternator is outputting more than a handful of volts. Because alternators are paralleled, all will share the same output voltage. You'd have to disconnect an alternator to tell if it was operating, or sense its current, or insert diodes. IMO diodes are out due to waste & expense - I'd try for some PWM instead. But if used, they definitely need to be 2-wire types so the alternator can correctly sense the battery voltage and hence compensate for the diode voltage drop (which varies with current thereby adding its own non-linearity to what the alternator's voltage regulator already has to deal with).    But 200A diodes, each wasting probably over 100W of heat at 100A with a 1.0V diode drop...? That's far from my preferred choice! So a suitable AC alternator does solve (all) your problem(s). Something with the same RPM of similar output. (If smaller, the alt should be self protecting. If bigger, the engine might stall under higher loads, but limit your loading - maybe interlocks or load-shedding abilities.) Merely a case of reliable dialog between the engine and new alternator... alas that involves heavy metal things like mechanics... (My preference: sledgehammers and heating spanners over blades & welders & other tools. But that's all part of the design & its suitable implementation. And wherever possible using standard items like links & couplers.) For such things I do my own wiring, but I understand wiring requirements and would most likely review them or seek advice... Of course you know how good but unlicensed installs are detected - they are far to neat! ..."But honestly Sir, he was a fresh-out Lektrishun - you know, the rare ones still with unreality in their eyes - with his supervisor...". Actually, make that HER supervisor... this isn't becoming a discrimination issue is it? Tho that reminds me - "earthing" and "power sources"... where earthing means to an Earth-stake as opposed to (normal) chassis 0V battery grounding... I have not kept abreast but a decade or 2 ago there was advice or even insistence that earth-stakes or equivalent were to be used. Now whilst that may be valid (& IMO essential!) when interconnected with or similar to a typical domestic AC distribution, in other cases it is probably a no-no - why create a new hazard and extra risk? AC lines can be floating. Normal chassis grounding looks after fusing and equipment protection. AC sources with a line-current imbalance due to a leak or electrocution can be isolated by RCDs (Residual Current Devices, aka (earth) safety switches etc). If you come between an AC line and provide a suitable path you become what we in the trade call electrocuted. [No, no puns.] But why provide that path intentionally? If you "earth" a floating AC line you become its voltage reference. But the hazard is then if a 2nd "fault" exists... (But earthed distribution is the norm for large or widespread AC systems.) I was quizzing the business opportunity tho I suspected a hostile environment - eg the low volume and non-stanardisation involved. There's always the posting of what you eventually do so that others may benefit, but afaik the12volt isn't about commercialisation, it's about solutions to problems. IMO the ability to repair some discontinued device to regain irreplaceable functionality... but why did I waste it on a 49 year old ute!? (..!!) Or in my case, the ability not to spend as much money... IMO it would be easier fitting a single AC alternator than 2 or 3 alternators thru heir gearing for whatever speed they need for desired output. But as before, if your DC loads outweigh your AC loads.. Of course dc alternators to dc-ac inverters need a battery in between, and for a few 160A alternators I'd expect more than a few batteries... I think that's covered the main stuff. Things like how carby speed governing works... It just does - it varies the butterfly hence fuel intake to keep constant RPM. If the RPM drops, it increases torque by adding more fuel (opening carby butterfly) - no different to electronic RPM sensing and adjustments to injector duty cycle. I revisit aka google such detail if needed. [These days my knowledge needs are usually only tactical. Even organised long-term strategic leaning is rare. But to learn or relearn something for the mere filling of old potholes or sake of knowing...? Nah - not generally for me - except perhaps for certain non-technical itches.]    And of course a gas engine will not run faster than its equivalent diesel (for a 3000 or 3600 or whatever RPM alternator). (That was in an older reply...?)

This thread has answered a question of mine, so I will chime in with what I know in hope that it helps someone else. I don't know much about speed regulation on some of the newer units with electronic controls, but with a typical industrial type engine that operates at a fixed RPM, speed is regulated by a mechanical governor connected to the throttle. In some older small engines, a set of weights are affixed to a gear which is driven by either the camshaft or the crank. The weight set is connected to a lever, a spring, and then the butterfly on the carb(gas engine). When engine speed slows(more load), the weights move in(less centrifugal force) and the lever pivots to open the throttle butterfly. When speed increases, the weights move out(more centrifugal force) and the lever pivots to allow the throttle butterfly to close. In other engines, the governor lever is moved by the air speed from the flywheel. There are other systems, but they all do the same thing: regulating fuel delivery to keep the engine running at the desired speed regardless of load. The APU alternator head can likely be repaired. If it uses brushes, then there is a possibility that they have worn out and just need to be replaced. On the other hand, if there is a fault with either the stator or rotor, then one or both would need to be rewound or otherwise repaired. It's an avenue you might want to consider...brushes should be very cheap. The APU manufacturer was probably just an assembler of the engine/alternator/electronics(if present) so it's unlikely that they would develop and use a proprietary brush in the alternator. Of course, that also assumes that they didn't use a brushless design. All that being said, if repair is not economical, then replacing the alternator would be the next best route. I'm assuming that the alternator is direct drive, meaning it is directly coupled to the engine's crankshaft. In all of the direct drive "generators" I've seen taken apart, the crankshaft has a taper which mates into a corresponding female taper in the alternator head. The taper is a "locking taper" design, but manufacturers add a through bolt to ensure that it doesn't come apart. By removing this bolt, inserting a slightly larger diameter of round stock, and giving said round stock a few sharp raps with a hammer, the alternator can be removed from the crankshaft taper for replacement or repair. The alternator may or may not have have more bolts mounting the housing to the crankcase of the engine. One thing of note is that there are two completely different tapers that I have found reference to, J609A and J609B. Apparently these are S.A.E. specified in terms of taper per foot and mounting flange pattern. You'll need to determine which one you have to secure the proper replacement. Since the APU has a diesel engine which I presume runs at around 1800rpm(not an inverter type), you'll need to dig a little deeper and find a four pole alternator. The typical two pole alternators are designed to run at 3600rpm on a gas engine and would only produce around 60 volts at 30hz frequency(if I remember correctly) if coupled to an 1800 rpm engine. The four pole versions are not anywhere near as easy to find, but it's also possible that I just don't know where to look. All in all, it should be cheaper to fix or replace the APU alternator than adding three more to the truck engine and buying an appropriately sized inverter. You'll just have to find and contact an electric motor rewind shop to find out. Good luck. P.S. Once in a while a "dead" alternator head on a generator set can be revived by simply plugging in a hand drill set to turn clockwise, depressing the trigger, and then manually spinning the drill chuck counterclockwise. If there is a fault in the windings of the rotor or stator, this won't help, but if it has lost residual magnetism then this will flash the field and sometimes get it generating power again.