48V Alternator/Generators for automotive use? Do they exist? - Page 1
Forum section: electronics / general

author: rx8pilot
author_rank: Super Contributor
timestamp: October 24, 2018, 10:26:08 pm
content: I had a conversation with a friend that is building a commercial vehicle that has a lot of equipment that needs a lot of power. His plan (the company building the vehicle) are basing it all on 12v inverters and a huge LiFePO4 battery.The max load is about 5kW and averaging about 4kW or so. That is a range of 325A to 400A which is pretty ridiculous in a vehicle. I know people do crazier things with car stereos, but this is a commercial system that is expected to be very high reliability. They have 4/0 cabling, massive fuses, huge distribution blocks, giant ring terminals. Kinda nuts.I asked if anyone considered 24v or even 48v as a technical buss to power all the sensitive gear. Far more manageable cabling, distribution, fusing, etc. 48v sine wave inverters are regular off-the-shelf products from many manufacturers, 48v to any other common DC voltage are also regular off-the-shelf products. The only thing that would seem to be a challenge is that I have not seen any 48v alternators that can be installed in the auxiliary accessory position on the engine. I have seen industry articles that car manufacturers are likely moving to 48v systems - but I don't see any commercial items on the market.Anyone see a 100A 48v vehicle based alternator/generator? My Google-fu is either weak or they are a unicorn. Found one random, no manufacture one Amazon of all places - but I am thinking of a reputable brand with high-reliability.Maybe putting (2x) 24v in series? Spitballing here on a topic that is outside of my wheelhouse.

author: langwadt
author_rank: Super Contributor
timestamp: October 24, 2018, 11:51:09 pm
content: https://www.ebay.com/itm/362454809374?

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 24, 2018, 11:54:50 pm
content: What about a 240V generator?

author: rx8pilot
author_rank: Super Contributor
timestamp: October 25, 2018, 12:19:21 am
content: Quote from: langwadt on October 24, 2018, 11:51:09 pmYes - that! Although when I looked at the manufacturer website, they say they only have up to 28v. No evidence they make a 48v.Quote from: NiHaoMike on October 24, 2018, 11:54:50 pm240AC??

author: station240
author_rank: Unknown
timestamp: October 25, 2018, 01:06:06 am
content: After I bit of poking around, I found your problem.For 48V they make the starter motor and generator into one unit.So you need to search for "48v starter generator"Might be case of finding a vehicle that has this equipment, and buying spare parts.https://www.valeo.com/en/48v-affordable-hybrid/https://jalopnik.com/everything-you-need-to-know-about-the-upcoming-48-volt-1790364465

author: dcarr
author_rank: Regular Contributor
timestamp: October 25, 2018, 03:06:28 am
content: 24V alternators and other parts are fairly common due to heavy trucks/buses/marine/aircraft. I think that would be the way to go if shifting away from 12V---at least the current gets cut in half. Delco Remy makes some models that could support the loads you mentioned:http://www.delcoremy.com/Alternators/Find-by-Model-FamilyDavid

author: Ian.M
author_rank: Super Contributor
timestamp: October 25, 2018, 05:17:54 am
content: Putting over 3HP through a belt drive will be problematic - it can be done but tends to result in poor belt life and the side loads required for adequate belt tension can cause premature bearing failure of the drive shaft and/or alternator. IMHO two 24V alternators, one of them isolated ground so it can be 'floated' to charge the top half of the 48V battery bank, would be well worth looking into. They should have separate belts, and the angle between them should be as great as possible, preferably in excess of 120 deg so most of the side load cancels out at the drive shaft.

author: rx8pilot
author_rank: Super Contributor
timestamp: October 25, 2018, 05:47:25 am
content: That makes sense..... and uses common parts. Curious how to safely float it.Quote from: Ian.M on October 25, 2018, 05:17:54 amShort and misplld from my mobile......

author: Ian.M
author_rank: Super Contributor
timestamp: October 25, 2018, 06:02:23 am
content: Isolated ground alternators are fairly common in marine applications to prevent corrosion due to stray currents.

author: Whales
author_rank: Super Contributor
timestamp: October 25, 2018, 08:38:26 am
content: Step back a sec.Car alternators have a field winding (rather than permanent magnets). You put current through this and change it to control the output voltage. The 'voltage regulator' unit that controls this field current is sometimes separate (older cars) or built into the alternator (most modern cars?).How far can this be controlled? Perhaps all you need to do is mod this. Power output will still have to be respected, and you might need to check/replace the rectifiers on the alternator if they can't handle the voltage, but that's all doable.Nonetheless 5KW is a hell of a lot of power. Car alternators don't put out anywhere near that much. 110/240V motors will probably be much better options to look at -- they don't necessarily have to output 110/240V.

author: Ian.M
author_rank: Super Contributor
timestamp: October 25, 2018, 09:42:41 am
content: Uprating a 24V alternator to get 48V (nom.) at high currents isn't going to work reliably without rewinding the stator, even if you replace the diode and regulator. You'd have to double the flux from the field coil on the rotor, which would require twice the current through it, resulting in four times greater Joule heating of the rotor, which IMHO is likely to result in it burning out.5000W is under 105A at 48V. That's well within the capabilities of a pair of Balmar 24V alternators from their extra large frame product range.http://www.balmar.net/products/extra-large-case-alternators/They have isolated ground as standard, so floating the top one in a 48V (2x 24V) system should be easy.You'll need a pair of suitable regulators for them to match the battery technology and configuration you are using.http://www.balmar.net/multi-stage-regulators/Check with Balmer for supported LiFePO4 battery configurations, whether the top regulator will need isolated mounting, and any advice they have on use in a 48V system.

author: amyk
author_rank: Super Contributor
timestamp: October 25, 2018, 11:50:26 am
content: 400A at 12V is doable... multiple alternators in parallel is probably easier than trying to float one.Something like this...

author: DenzilPenberthy
author_rank: Frequent Contributor
timestamp: October 25, 2018, 02:49:52 pm
content: Trying to generate 5kW from the engine's belt driven alternator is not the right way to approach this.Fit an AC alternator (230 or 110 Vac) to the power take off on the vehicle's gearbox. You say it is a commercial vehicle so it should have one, or at least an option to fit one. If you want batteries so you can run your system without the engine on (but really? at 4kW load?), charge the batteries from the PTO alternator via a battery charger.Could be cheaper and easier though, if you are using it a lot, to fit a 5kVA diesel generator somewhere in the vehicle as you could run that on untaxed fuel and save running the vehicle engine all day.Edit: I don't know anything about fuel tax in the USA. Here in the UK you can buy diesel that is dyed red which has no 'fuel duty' paid on it so is about half the price of undyed diesel for road use. If you are running your vehicle's engine to generate power it will still need to run on 'white' diesel. A separate diesel generator can run on 'red'.

author: schmitt trigger
author_rank: Super Contributor
timestamp: October 25, 2018, 03:00:54 pm
content: I second the idea of a secondary 120/240 volt commercially available generator. It would be perhaps cheaper than all the massive cabling, fuses and connectors.If you run this generator from LP gas, it should be very clean.

author: duak
author_rank: Super Contributor
timestamp: October 25, 2018, 07:11:56 pm
content: It's not quite true that you have to increase the excitation voltage of an alternator to get a higher output voltage. They'll happily put out a higher voltage if you increase the RPM since Vout is a function of Vexc * RPM. However, there will be a limit at some point, either magnetic, mechanical or thermal. Note that the rectifier diode triads have a low breakdown voltage, probably 50 V peak, so there's probably not much margin with a 12 V alternator on 24 V and up.One goofy idea is to look for positive ground alternators as many large vehicles are or were positive ground until the 70's. Two alternators could give +/- 24 V. I understand that aircraft also use higher voltage DC (28 V?) but I'd bet anything aircraft costs $$$.For a few years in the 90's & 00's 42 V was going to be the new automotive standard:https://en.wikipedia.org/wiki/42-volt_electrical_systemI don't think it went further than a few models from some manufacturers. However, when I looked for it, I saw some blurbs about 48 V systems coming in as a new standard for small hybrids.Cheers,

author: Bratster
author_rank: Frequent Contributor
timestamp: October 25, 2018, 07:45:54 pm
content: Quote from: DenzilPenberthy on October 25, 2018, 02:49:52 pmWe have the same dyed red diesel fuel here in the US for off-road use.I would vote for a generator as well. Either diesel or propane.I see that on some of the big power company service trucks, saying something like "emisson friendly APU onboard"(Auxiliary power unit)Instead of using the truck engine to be a poor generator use a dedicated generator.Sent from my Fi Moto x4 using Tapatalk

author: rx8pilot
author_rank: Super Contributor
timestamp: October 25, 2018, 08:33:20 pm
content: So I asked a few more questions about how the vehicle builder is configuring this thing.....They have a small-ish 12v alternator that is capable of about 125A at idle. They have 400Ah LiFePO4 battery pack (yes 400aH at $8700) that deals with short-term full loads. They have no expectation for continuous operation, but the actual runtime would be hard to predict at any given moment. The user would have to know exactly what the load is, the state of charge, and the charge rate to get an idea of how long it can run. Seems like a PITA to me. He is planning to use UPS's to keep everything alive while switching to shore power when available or possibly a small generator. That is a compromise from what he originally was hoping for.There is limited space for an on-board genny. The genny would need to be better than average for reliability, low noise, and electrical quality which generally equals a larger unit.I am wondering if my idea of having a primary 48vdc bus is a good idea.Conceptually, I am thinking:It needs multiple sources of power - The vehicle engine, shore power, large battery bank, and maybe an on-board genny for 'emergencies'It needs to output - 120VAC, 12VDC, 15VDC, 28VDC, and 5VDC.I was thinking that having a 48vdc system bus, everything could feed that with relative ease and manageable cable size. 2x 24 isolated alternators in series is not a bad option. The external AC input is easy to convert to 48v with off-the shelf power supplies, 48v battery and charger is easy, 48v to pretty much any voltage/current requirement is easy and off-the-shelf, 48vdc sine wave inverters are easy and common.This, to me, seems like an easy way to switch between numerous sources of power while having the 48v battery bank keep it alive as long as needed. Allowing the user to simply start the engine and disconnect the shore power without any switching or planning. If the engine has been idling too long, fire up the on-board or external genny and turn the engine off. All the loads would have a reasonably stable 48v bus all the time regardless of where the power is originating.Does this logic sound reasonable? It is not my project or my money - but it is an interesting problem - a mobile unit with 5kW of continuous power that can come from multiple sources without interruption.

author: richard.cs
author_rank: Super Contributor
timestamp: October 26, 2018, 12:13:13 pm
content: I have seen 48 V and 60 V d.c. systems in UK military vehicles but 28 V is much more common. It was a while ago but from memory it was a multiple-output machine that produced 48 or 60 V DC and 240 V a.c. and was direct-coupled without belts. No idea what it was used for.Options for getting 48 V from one of more 24 V alternators include:1) Stacking two in series, isolation needed on at least one, but some thought also needs to go into keeping the regulators happy. Or with identical alternators you could put the two field windings in series and use a single 48 V regulator, that might be best actually.2) Getting 48 V out of a 24 V one by fitting a 48 V regulator. The trick is to make it so the field current cannot exceed the design value even if it comes from a 48 V source (could be as simple as a resistor equal to the field winding resistance). There's no point trying to double the field current - even if the winding survived it wouldn't work because the thing will just saturate. Instead you simply accept that the cut-in RPM is two times higher. i.e. if you take two 24 V alternators that are designed to give full output at 3000 rpm (say 1000 engine revs geared up 1:3) then they will give full output at 48 V from 6000 rpm (2000 engine revs). You can't simply gear them up if they're on the vehicle engine as they would then be destroyed at high engine revs in normal driving so you have to set the engine revs higher when generating instead.3) If a 24 V alternator of suitable output power can be found strip it down and remove the rectifier. Feed the three-phase high frequency AC into a transformer to double the voltage, then rectify to 48 V and drive with a 48 V regulator. Essentially the only high current bit is between the alternator and transformer which can be kept nice and short. The transformer may need to be custom made but it's not hard to find someone to do that, and it can be small and lightweight because of the high frequency. This behaves like a 48 V alternator

author: schmitt trigger
author_rank: Super Contributor
timestamp: October 26, 2018, 01:04:26 pm
content: Curiously, the New York Times has an article today mentioning 48V system in vehicles.The reason: an "e-booster" for turbos. Turbocharged engines offer many advantages, but they suffer from turbo-lag.Attached a link to the article, which deals mostly with the future of forced induction on gasoline engines. Interesting read overall. The e-turbo is discussed towards the end.https://www.nytimes.com/2018/10/25/business/turbocharger-cars-vehicles-power.html?emc=edit_th_181026&nl=todaysheadlines&nlid=371077491026

author: langwadt
author_rank: Super Contributor
timestamp: October 26, 2018, 02:20:41 pm
content: might try googling for 56V instead of 48V