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Alternator Excitement.........

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  • neiowa
    replied
    Thanks. Interesting. At gov speed the alternators don't reach rated capacity.

    I'm surprise that the LED compartment lights add up to as much as they do.

    Leave a comment:


  • zfdtruckman
    replied
    neiowa,

    Here is the electrical analysis report I promised.
    Attached Files

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  • Catch22
    replied
    Originally posted by firenresq77 View Post
    What are you going to do with a lawn mower on your truck??????
    Let me try again....MDT

    Leave a comment:


  • firenresq77
    replied
    Originally posted by Catch22 View Post
    (we're looking at MTDs and some other little things that add up).
    What are you going to do with a lawn mower on your truck??????

    Leave a comment:


  • Catch22
    replied
    Originally posted by Frmboybuck View Post
    NEiowa, If all your lights will be LED, your amp load will be nill on those. LED lights are extremely efficient and require very low amperage.
    We got to thinking this, then we remembered some things. We install flashlights with charging bases, TIC charging base, mobile radio, portable radio chargers.... Then we considered that our ground lights weren't LED, niether were the pump panel lights and some other items. Gotta keep in mind the add-ons and the like, as well as things you might add in the future (we're looking at MTDs and some other little things that add up).

    Leave a comment:


  • Frmboybuck
    replied
    NEiowa, If all your lights will be LED, your amp load will be nill on those. LED lights are extremely efficient and require very low amperage.

    Leave a comment:


  • zfdtruckman
    replied
    neiowa,

    Next time I'm at work I'll scan our electrical analysis report and post it. It's from a 2007 Arrow XT HDRP. It has twin Leece-Neville 270 amp alternators with 6 group 31 batteries. At idle the system produces 259 amps and at governed speed produces 468 amps. NFPA minimum continuous load is 115 amps giving us a reserve of 143 amps. The minimum continuous load on this apparatus is far less than our previous deliveries due to switching over to as many LED lights as possible.

    Make sure you have plenty of reserve. After delivery, we installed 5 radios and a 12 volt bank charger for 6 portables. You would be suprised as how much of that reserve you use as other equipment is installed over the life of the vehicle.

    Leave a comment:


  • chiefengineer11
    replied
    The load calculations are something that the apparatus manufacturer should provide you. It should be included in the proposal. You need to double check it. You need to know how many amps each item draws and add them up. Each light, each heater motor, the A/C unit, each item that's sitting in an onboard charger, everything that consumes electricity. The starter motor and the siren don't get counted. The primer motor should be taken into consideration, although it only operates for a brief period.

    Leave a comment:


  • neiowa
    replied
    Right. But what I'm getting (more than one builder) is "get the 270 amp don't want to come up short" That's easy when some else (the FD) is writing the check. At the point of cutting out $ and I'm thinking just stick with the 160amp (unless can demonstrate need for additional). Our 1985 pumper has only a 90amp (long before LED) and has been no issues.

    So if anyone has recent load calculations for a pumper would be interested in what your results are.

    Leave a comment:


  • chiefengineer11
    replied
    I guess I should have gone back and looked at earlier posts, looks like I'm repeating myself and others. But maybe it bears repeating, the subject's too important.

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  • chiefengineer11
    replied
    Anyone who's bidding should be able to provide you with their load calculations, including how they arrived at the figure. Here's an item from our specs.

    "An amp draw report for the proposed vehicle is to be provided with the bid. Vehicle manufacturer shall calculate current required to operate all electrical devices of the completed vehicle, except the starter and siren.

    The alternator shall be capable of supplying at least that amount of current at 200F (93C) at the engine manufacturer’s stated idle speed without drawing on the vehicle batteries. The alternator shall not exceed its manufacturer’s stated maximum rotor speed at the engine manufacturer’s stated maximum engine speed."

    T.C. and others may suggest making it 110% of that current, and I won't argue the point.

    A key point is that the alternator has to do that with the engine idling so that you don't run out of power when you're idling, and you don't start shedding loads. Many alternators that come with trucks, and many of the lower rated ones won't make it until you get the engine speed up around 1000 RPM. Some will do it at a lower temperature, but not at the higher temperature. You need to look at the alternator's power curve. Leece Neville and Niehoff both have them available on their web sites. I'm sure that other suppliers do, too.

    Look at performance curve. Usually the RPM shown is the alternator RPM, not the engine RPM. So you'll also need to know what the drive ratio (pulley sizes) is.

    This is not someplace where you want to come up short, but at the same time, you don't want to overdo it. Big alternators take up space and power. They need adequate air flow for cooling and belts to turn them. They need really strong brackets to support them. These are all places that some truck builders will skimp. But having to correct for it several years later can really cost BIG BUCKS. It all comes down to know, don't guess.

    Stay safe out there, everyone goes home!

    Leave a comment:


  • neiowa
    replied
    Bump. Specing our new pumper tanker. Commercial chassis. Will have a 110V generator for flood lights.

    Apparatus guy says should have a 270amp. BIG $. Like +$1200 to go from 160amp to 270amp. Why? LED compartment lights, LED warning lights. Some 12V scene/ground/misc lights. Radio and beer budget siren. As I recall our current 1985 pumper has a 120amp +/- and never had a shortage of 12vDC power.

    So why waste $ on a oversize alternator? Anyone added up the actual 12V load on LED equipped pumper?

    Leave a comment:


  • chiefengineer11
    replied
    Originally posted by FWDbuff View Post
    We solved this problem at the advice of a well known, well-reputed automotive electrical consultant (who also happens to be a Federal Signal Dealer and a volunteer fire officer himself......)from South Jersey.

    We spec's our new engine's alternator to "be able to supply maximum system draw, at engine manufacturer's idle speed, at 200 degrees F." or something to that effect. I'll get the exact wording later. Perhaps Chiefengineer11 will see this in the meantime and chime in.
    Sorry, folks, but I was out of town for a couple of days, no access to a computer, so I'm just now catching up. Here's the text that FWDbuff is talking about.

    "ALTERNATOR An amp draw report for the proposed vehicle is to be provided with the bid. Vehicle manufacturer shall calculate current required to operate all electrical devices of the completed vehicle, except the starter and siren.

    The alternator shall be capable of supplying at least that amount of current at 200 degrees F (93degrees C) at the engine manufacturer’s stated idle speed without drawing on the vehicle batteries. The alternator shall not exceed its manufacturer’s stated maximum rotor speed at the engine manufacturer’s stated maximum engine speed.

    Installation of the alternator shall conform to TMC RP 101B. The entire electrical system of the completed vehicle, including the generator set and its installation (described below) will be surveyed by Vineland Auto Electric Co. of Vineland, N.J. as part of the purchaser’s acceptance tests."

    The logic for it is this: All of our electrical devices are important to us, and we want them all to be available and working at all times. Load shedding might be OK in the event of a failure of the alternator, but not as a matter of routine operations. So we demand that the alternator that we us be capable of doing just that.

    Many of the alternators out there will put out the required current at elevated engine speeds, but not at idle. Unfortunately, engine company operations sometimes require us to be at idle or lower RPM than will give full output for some of these units. Others will cheat and use a small drive pulley, but that runs the risk of overspeeding the alternator rotor when you're on the road at near maximum engine RPM. Many alternators have a maximum rotor speed of 8000 rpm. Put a pulley ratio of 1 : 4.5 and do the math. Some alternators will meet spec at the 72 degree F test but not at 200. But the underhood temperatures we encounter, even with good air flow, require that it perform at the higher temperature. Performance of all units will degrade as temperature increases, so that has to be taken into account.

    Not too many alternators are truly capable of performing to that standard. The ones that will are quite expensive and require plenty of air flow for adequate cooling. But underhood/under dog house space is becoming tighter and tighter. The physical dimensions of an alternator that will do the job are pretty big. And the unobstructed space needed to move air over it is, too. And the 2007 engines will just aggravate matters.

    We're partly to blame. We want more space in the cab, or less hood to have to see over. We want to keep costs down. The manufacturers are looking for ways to underbid the competion. So what do they do? To paraphrase the above mentioned consultant's words, they go to this great cop-out, the load shedding device. Worse yet, since they have all the drag on the 1901 committee, they get NFPA to require it. That's so they can get away with a lesser alternator.

    There's one saving grace. The alternator that we're getting is not the one we originally had in mind. There's only one or two that we've found that will meet spec with the loads we had projected. But by changing all of our warning lights (except two small ones) over to LEDs we've reduced the load down to the point that others will do the job.

    But thanks to 1901, even though we can now make enough electricity to keep things running properly, we're stuck with paying for a load shedder, something we don't need and don't want. Well, maybe not. It appears to be programmed into the V-Mux.

    Some manufacturers have gone over to using two alternators. That idea does have a lot to recommend itself, and I'm sure it has its share of problems, too. In this case, whatever keeps the lights on is OK with me. Just don't start shutting stuff I'm using off on me because you don't want to give me enough power to do the job.

    Stay safe out there, everyone goes home!

    Leave a comment:


  • raricciuti
    replied
    We are in the middle of bids for a new rescue, and we specified a new type of alternator that has a permanent magnet, instead of a field circuit. It's made by Eco-Tech (http://www.eco-techalternators.com/alternators_14.htm). It's a 305 amp unit designed to put out about 240 amps at idle. Most 300 amp alternators can't manage 100 amps at idle.

    Hopefully this thing will be a cure for low DC voltage at idle. Engine management systems really get jiggy when the voltage drops. And we're trying to avoid a high idle, as most rescue scenes have enough noise without having a 450 horse behemoth cranking along at 1800 rpm right next to the incident. Anyone have one of these?

    Leave a comment:


  • Rescue101
    replied
    A lot of modern alternators are internally regulated,self "exciting" units.But to get them to charge initially,you need to raise the rpms to over 1000-1500 depending on the unit.While an alternator will charge at idle,most like to see a little rpm,usually in the 1000 range to get them to perform well.As FWD says(and a lot of specs require.,I believe NFPA included) full output at idle with max load on.No load should be a breeze.An 84 unit could be either internal or external regulated not that is would matter.Probably a LN,and probably near the end of it's service life if it was original.Does this help? T.C.

    Leave a comment:

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