Please define "Hot Shift" for a hydraulic generator.
Does it mean shifting under a load at any RPM?
Do Amps, Smart Power, Hartagen, Harrison, & Onan use the term for the same thing?
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Thread: Hot Shift Generator?
12-16-2002, 10:01 PM #1
Hot Shift Generator?
Last edited by AC1503; 12-16-2002 at 10:03 PM.
12-17-2002, 06:08 AM #2
A "hot shift" PTO (power take-off) allows you to engage / disengage the unit while the engine is running. While the PTO may be capable of doing this under load at any speed or RPM, make sure that the manufacturer of the generetor (or whatever else is connected to the PTO) can handle that. In the case of AMPS generators, they must be equipped with their "Soft Start" feature if a hot shift PTO is used, or else bad things will happen (read: breaking expensive parts). I believe that all of the currently manufactured AMPS electronically-controlled units have this feature standard, but be sure to check before purchasing. The other common type of PTO is a "constant-mesh", meaning that it is always engaged. When you start the engine, the PTO spins. The down side to these is whatever is connected to the PTO is being powered all the time, whether you need it or not. Another potential problem is should a hydraulic line fail, you can't run the engine at all without destroying the hydraulic pump - they can't be run dry, and there is no way to shut off a constant-mesh PTO. Always check with the manufacturer of the equipment to get the correct info before you spec a generator (or anything else for that matter). They're way too expensive to just wing it.R.A. Ricciuti
Mt. Lebanon Fire Department
01-09-2003, 01:54 PM #3
- Join Date
- Dec 2001
- Sugar Land TX
Dear raricciuti & AC1503
I normally have people contact me privatly for better communications on brand specific questions, but in this case I will make an exception. First and foremost, I don't want anyone to misconstrue this reply as a sales pitch. I would never use this forum to "sell" my product, but there are some publically asked questions here that require correct and definate answers.
Yes raricciuti , you are correct. All AMPS generators come standard equipped with an electronically controlled "soft-start" with every unit. This feature, along with many others, was added about a year ago and called the eHP series.
I will add to your explanation of Hot Shift PTO and soft starts.
When a Hot Shift PTO is engaged the engine is already running. There is a seperate switch for the PTO to engage. Do not confuse this switch with the generator excitation switch, they are two seperate switches with two seperate functions.
(or at least with our systems they are supposed to be)This switch literally engages the PTO to the transmission and it is at that point that you get pump rotation, thus turning the generator. Most PTOs step the RPMs up, so there is an instantanious pressure spike transferred to whatever the PTO is pushing, i.e. a hydraulic pump. If that pressure isn't relieved ro diverted, that is where dammage can occur,(see purchasing expensive parts) This is where we saw most of our problems a couple of years ago. Blower wheels came apart, diode packs came flying off, and internal pump dammage was suffered.
I am not sure about Muncie, but I know that for most applications with Chelsea PTOs, your engine rpms have to be below 1000 to engage this type of PTO.
AMPS is not limited to this restriction anymore because of electronic controls and the soft start mechanism with the eHP series. The AMPS unit is now able to engage at any RPM. Once again, do not confuse this with generator excitation. All brands, Harrison, AMPS, etc. can remote start the generator excitation at any rpm and any load, but until now no brands could tollerate literally engaging the PTO at higher RPMs such as 2100rpm.
AC1503, to answer your question about shifting while under loads. I can't answer for the other manufacturers, but AMPS promotes the fact that you CAN engage the Hot Shift PTO with the generator excitation already on and a full load already applied to the generator. This is also another feature of the eHP series.
In all fairness, I do know that Harrison is comming out with electronic controls also. I believe they already have a couple units in the field. I am not sure if this capability or the high speed engagement are some of thier new features.
I would check with Jim Otwell or John Mann on that subject.
AMPS recommends that all installations utilize Hot Shift PTOs instead of constant engaged. The reason being is the eHP series was designed to work with Hot Shift PTOs. Another reason is if you should ever suffer a broken hydraulic line connecting one component to another. On a "constant mesh" PTO, that will shut the entire truck completely down until you remove the pump. With a Hot shift, you simply dis-engage the PTO and you're still in business. It is my opinion that no matter what brand Hydraulic generator you use, you should always utilize a Hot Shift PTO.
I hope that this has answered all of your questions, but if not please feel free to contact me directly at firstname.lastname@example.org
As I said earlier, I hope that I haven't offended anyone by being brand specific, but these are the facts straight from AMPS.
Scott DixonScott Dixon<br />Director of Sales & Marketing<br />AMPS
01-09-2003, 10:46 PM #4
- Join Date
- Jun 2002
HotShift vs. constant mesh
The issue of hotshift is pretty well stated previously. I now have 25 hydraulic generators in service and am awaiting delivery of two more pumpers with hydraulic gensets. All, except one, are hot-shift. The one was a special install where a standard Hot-Shift PTO would not fit under the cab. It functions well, but has inherant problems. Any constant mesh unit will display higher than normal wear on the constant mesh gearing caused by excessive idle times on fire apparatus. As you are aware, when a diesel idles it creates elevated pulses that are transmitted throughout the crankshaft mounted items. Off idle, there is no problem. The constant mesh units are subjected to the hammering pulses of the idle time service. This is not an issue with the Hot-Shift units, as there is not attachment of accessory load at idle with the hot-shift in the "OFF" position. If there is no need to beat it to death, why beat it to death? Go with the extra cost and function of the Hot-Shift. Even with the electronic units, place the system in and out of operation at lower RPM's whenever it is possible.
01-10-2003, 03:20 PM #5
Our new aerials are equipped with Smart Power hydraulic generators. They activate by hitting MODE button on shifter panel. It will not come on until RPM's fall below 1000rpm.
Smart Power is about all that is being used in our area. Just about all types (Harrison, AMPS) have been used with some problems (dont know details, just what has been told by other departments).
FYI::: Harrison carries NO product liability insurance. Sutphen installed in a new engine, while pump testing fitting (within the generator) came loose and sprayed fluid all over exhaust causing fire that totaled unit. Harrison says too bad. Dont think I would spec a truck with a Harrison unless they could provide proof that they NOW carry product liability insurance.
01-12-2003, 12:12 PM #6
It is my understanding that some PTO clutches are rated for a higher start load than others. Example, in Brand X you can start your AMPS generator with a full load and at high engine RPM's, but try it with Brand Y and the clutch pack is likely to come unglued after a few uses. Is there any truth to this, or is the Brand X rep blowing smoke up my pipe?
01-13-2003, 10:40 AM #7
- Join Date
- Dec 2001
- Sugar Land TX
It doesn't sound like their blowing smoke, they may just be
mis-informed or not up to date on new technology in hydraulic generators.
It also depends on how old the system is. If it was built before November, 2001 then this is certainly the case. You must be below 1000 rpms to engage the PTO or dammage will occur. The ability to engage the clutch at high rpms wasn't available on any system, AMPS or otherwise, until the eHP series. The first production units went out in November, 2001.
Now, there are some PTOs that have a higer torque rating than others. For instance Chelsea has their 267 & 277 series PTOs and then they have their 859 and 866 models. The 267 and 277 models are the most commonly used for hydraulic generators on HD4060 and M 3060 transmissions. Then there are the 859 and 866 models. These are for different applications that demand more torque,like running two large pumps "piggy back" off of the same PTO. To my knowledge, the intention isn't to offer a high speed engagement ability, but instead more torque availability.
You or the company you are refering to may contact me privately to discuss this matter further if you would like.
My phone # is 281-240-2555 or e-mail me at email@example.com
ScottScott Dixon<br />Director of Sales & Marketing<br />AMPS
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