How much power (kw's) do I need for my home?

[tim292stro]

Currently the design is centered around a scooter CVT, and fully variable engine speed from idle to red-line. I'm still talking to the CVT vendor (custom "shift" tune), but I can share more details in the FOBIC build thread when I have them ready. Basically, per the engine manual I'm supposed to have 5-minutes warm-up, 5-minutes cool down with no load. With a custom controller doing auto-start I can program those intervals into the software so it doesn't have to be remembered. The scooter CVT has an idle clutch, so I can start and stop without the alternator inertia.

https://www.youtube.com/watch?v=uCEvBGT8twM


In general I'll be looking at the output voltage, output current, alternator RPMs, engine RPMs, engine TPS. If the current draw from the batteries is large enough the generator will start to make up the used charge and support the load. I'll allow the batteries to discharge while the engine/alternator gets up to a speed that can get the alternator back in the regulation voltage range (too high a current draw causes the alternator voltage to drop). When the alternator is above the regulation range it will slow the engine/alternator down to bring the regulation range for the load. If it has been "floating" the batteries for a given time, it will idle, cool down, and shutdown. The battery pack output will be fused at 225Amps, and soft limited at 200Amps, so I can ensure that I can charge batteries and support the load of the system so I get the most out of the run time.

[EDIT:] Were you asking about the simple kick-up control circuit I described? If so it's "bang-bang" control - you would set the engine RPMs with the solenoid deactivated to you low or high RPM setting, and the engine RPMs with the solenoid activated to the other RPMs. Simple high-low control. [/EDIT]

 

[90cummins]

tim292
Your speed control and custom regulator sounds interesting so I'd like to mention some of my observations during the testing I performed.
I performed my testing using a 10hp diesel so capacity is limited. I found that the 1603 voltage holds at steady 28.5v and drops only because current output is limited due the operating speed.
One of the reason I'm driving the generator so slow is to limit loading on my engine.
I have been thinking that if I could adjust the output voltage down that would allow the battery's to assist the generator during a high load situation instead of attempting to put it all on the engine.
What are your thoughts on that?

90cummins

 

[tim292stro]

The whole reason I'm going with a custom voltage regulator and a CVT is exactly because the capacity is limited. If I was running in the 1800RPM range, and a sudden load of >200Amps was applied over what it was already generating, the engine would stall and die.

An alternator is what we call a "current source". The characteristic of these is that they will put out whatever voltage the current demand and the power for the rotational input can support. Interestingly we control the output voltage, by setting the input (field) current to this "electro-mechanical amplifier".

You can reduce the shaft load for the alternator by reducing the input current demand (field current) using a PWM or chopping circuit, this will have the affect of dropping the voltage as this is the very same mechanism the voltage regulator uses to control the output. However, the crux is, the voltage regulator might not like seeing the field "open" - in it's world the field is always controlled by the voltage regulator, and if it does not see a field coil load - it may throw a fault and stop functioning. If it doesn't happen to throw a fault, it will see the voltage is too low and try to bring up the voltage by increasing the field current - this in itself can lead to system instability because your control would have to react to both the load and the voltage regulator's reaction to your reaction to the load (yeah it's a logical mess), which is again why I'm building a "smarter" voltage regulator that is more of a system controller.

[EDIT:] I picked a V-Twin 18HP diesel and am putting on a GT1241 turbo to squeeze out 23-25HP, and tolerate any high altitude operation. I did this to roughly match the maximum power output of the alternator:

450A x 28.8V = 12.960kW
13kW (rounded up) = 17.433HP
17.433HP / 80% "ideal" efficiency of the alternator = 21.8HP
Throw in a few losses for non-ideal alternator and belt-drive losses (negligible), and I get a 23-25HP engine demand. [/EDIT]

 

[rustystud]

As requested here is the Niehoff performance data along with drawings for fabrication purposes. Hope you find it as useful as I did.
90cummins
View attachment 570329View attachment 570330View attachment 570331

This is the same alternator our buses use. We have had a heating problem with them in the past. We had to have a forced air system installed to blow outside air (out of the engine compartment) around the alternator.

 

[tim292stro]

Your busses use N1603 (Military SKU) not the C803 (Transit SKU)?

My '84 Gillig uses a C803, those which are designed for transit usually have a fan on the pulley side and a intake vent duct on the rectifier end (opposite of the pulley) which goes to a dedicated ram air scoop on the exterior of the vehicle above 8' (air is usually 10°F warmer at ground level).

For my generator design, the engine and alternator are set in two separate air spaces (mostly due to space constraints), with forced fresh air intake on the pulley side blowing into and around the case of the alternator and out the top of the enclosure.

 

[rustystud]

Your busses use N1603 (Military SKU) not the C803 (Transit SKU)?

My '84 Gillig uses a C803, those which are designed for transit usually have a fan on the pulley side and a intake vent duct on the rectifier end (opposite of the pulley) which goes to a dedicated ram air scoop on the exterior of the vehicle above 8' (air is usually 10°F warmer at ground level).

For my generator design, the engine and alternator are set in two separate air spaces (mostly due to space constraints), with forced fresh air intake on the pulley side blowing into and around the case of the alternator and out the top of the enclosure.

Most all transit agency's use oil cooling or forced air cooling , so no external fans. As far as a Military SKU # I didn't notice it. I was seeing an exact model of what our new buses are using.

 

[90cummins]

Getting back to the theme of my post, how much power (kw’s) do I need?
I have found that a 3.5kw generator is sufficient for the majority of my needs with 1 exception; we cannot use the electric dryer @ 5.2kw.
I have slowly acquired generators ranging from my small Honda EU2000i to a 25kw PTO generator and various sizes in-between depending on my needs.
In order to be more self-sufficient and to manage my power efficiently I installed a Hybrid 4kw Inverter that can handle inputs from a 24v battery source, solar, wind, hydro, and a generator. The feature most useful to me is the ability of this system to manage and assist a small generator’s output.
The (Gen-Assist) feature can be programed to (help) a small generator at a specific load by using battery power when the load exceeds the generators capacity, it can also handle unbalanced electrical loads.
When operating in this mode the inverter will allow the generator to supply all the electrical needs and use excess generating capacity to recharge & maintain the battery bank. If the electrical needs exceed the generator’s capacity the inverter will assist by using pulling power from the batteries.
During the evening hours from 6pm to bedtime we average 1kw usage with an occasional surge when the well pump kicks on, after that consumption drops to less than .5kw until the coffee pot is awakened at 6AM!
For nighttime I could use my Honda EU2000i that pulls fuel from a 3 gallon Marine fuel tank for essential circuits using a 6 circuit manual transfer switch.
Testing I did with the Honda resulted in 6 hours per gallon during the day which gives me a solid 24 hours if I include the 1 gallon in the Honda fuel tank, night time fuel consumption would be less.
The Honda is setup to operate the wood furnace, oil furnace, 2 small freezers, 1 refrigerator, entire living room with TV, computer, lights and pellet stove along with bedroom lights and electric blankets.
All these items total more than the Honda can support at the same time but properly managed and using 1 heat source at a time I can keep the load between 300 & 1500 watts.
The wood furnace motor has an input surge current of over 2000 watts so the blower motor must started first and the stack switch controlling it is put in manual-on for continuous operation to avoid the starting surge.
My wood furnace is my major 24/7 power consumer during the winter months and that now uses 236 watts (308va) after the installation of a high efficiency ¼ blower motor.
Over the past month I have replaced all of my lights (over 70) with 60 watt LED’s that consume 8.5 watts. I also replaced my porch rope lights (50ft) that used 242 watts with LED’s that now use 26 watts.
I don’t know what next but I’m open to suggestions!
90cummins

 

[Ratch]

That hybrid inverter sounds like an awesome device. I was going to home brew a similar system, using a 3.5kw UPS to run us during the overnight, and a genset to recharge it during the day.

 

[90cummins]

tim292
I need to ask why you need so much power?
How many kw's do you need to in your worst case at any given moment?
How many Kw's per month do you use?
Do you have multiple AC or heating units?
Do you have a very large battery bank to charge?
I like your concept just looking for details behind it.
One thing I've learned thru testing my system is that any resistance will cause considerable dangerous heat.
During one test I had a battery over-temp warning and had to shut down one of my tests due to excessive heat pulling 190A @ 28V 5.3kw.
I'm using 4/0 cable with crimped & soldered connections and I still had excessive heat build-up.
I need to review my connections to eliminate my heat issues.
My solution may be solid copper bar stock for battery interconnections.
Off to my local scrap dealer to see what's on sale today!
90cummins

 

[tim292stro]

Please just Tim.

First thing to note for my setup is I'm supporting a working camp, not a homestead - my run times are expected to be compressed, and need to both power the loads I've planned but also charge the batteries and shorten the run-time. One of the other considerations I've made is sound - since it's a camp, I expect quiet time to be a requirement in some circumstances. For example at some National Parks there is a quiet time between 8PM and 8AM, where generators are required to be shut-down. Personally I like quiet when I sleep (even though I'm half deaf), so I appreciate that requirement.

There are two or three battery banks that need to be charged: the 500Ah 24V generator bank, and the 250Ah 24V tent control bank. When the S-250 shelter is slid into the generator trailer, it also has a ~100Ah 24V bank to charge. That's about 280Amps of 28.8V I need just to charge the batteries over about 4 hours. You do have to be careful of the charging rate, or they boil over (even the AGMs I have to use).

The Base-X tents have windows, so day time lighting loads should be minimized if I can do open them - at night it could be as high as 720Watts. The S-250 shelter does not have windows and I don't plan on putting them in, as I want to retain the shielding shell as a "radio shack" - so lighting will be a demand day and night (about 48Watts max). The S-250 also has DC climate control combined with a refer unit (about 2kW), and a few cooking appliances (ration heaters 2x [430W each] and a microwave [1500W]).

Peak loads could theoretically exceed 13kW (battery discharge), sustained high loads may be around the 8kW range at the top-end of use (slight battery charge), but for the sake of run-time I'm planned the systems out to have a sub-6kW draw to allow for half the alternator output to run loads, the other to charge batteries. I do have a pair of SHC-35s, and I'm getting a pair of SHC-60s - those are self-powered as long as there is diesel available - I am looking at constructing or having constructed a set of four air-conditioners in the same foot-print as the HDT heaters, those will be 208Y-3phase direct from a generator on the towing truck for the setup, which also carries my backup 450Amp alternator that can charge the trailer/generator while the engine is running. Truck --> Trailer/Generator --> Camp (includes S-250).

Other loads are network equipment (about 250Watts total), ToughBooks laptops (120W each x 10), VoIP phones (15W each x 10), amplified speakers (20W each x 8 ), and two projectors (300W each x 2) - about 2.4kW of other gear.

What I'm hoping to do here is run enough solar (very, very quiet - have I mentioned that I appreciate quiet? ) that the generator never needs to fire up, but from a practical standpoint, I'm planning to have the generator cover whatever isn't handled by the solar during good charging times can be handled before "quiet time" is violated.

 

[90cummins]

tim29
Have you looked over the information I posted on the N1603?
I ask because I would like the ability to adjust the output voltage between 28.6v and 24v.
This is so it will work better with my battery backup system in load sharing.
90cummins

 

[DieselAddict]

Do you foresee any issues with the efficiency of the CVT in the system? Its going to cost you about 15% in engine output versus about 1-3% with a single speed toothed belt.

 

[tim292stro]

Tim,
...I ask because I would like the ability to adjust the output voltage between 28.6v and 24v...

I think I answered this already, but I'll add more information to help you make sense of it. This is not how automotive voltage regulators work - they expect to be the only power source in a system and are VERY simple as a result.
Here's an article on the logic that goes into them: http://www.embedded.com/design/real...ontroller-driven-alternator-voltage-regulator
What you will find will happen if you supply another power source is the one with the highest set-point will "win" (take the load). The voltage regulator will look at what what voltage is on the battery, if it's in the regulation range it will try to get the voltage to the set-point by either increasing the output to raise the voltage, or lowering the output to drop the voltage. If the voltage is outside the regulation range on the high-side, the regulator will most likely turn OFF the alternator field (no power output). If the voltage is below the regulation range the field will be on 100%. You may think you can share a load from two power sources, but if you read on how this regulation is done, you'd find that the alternator will be trying to get to the set-point while it's not really in control of the system - it will cyclically increase and decrease the output of the alternator hunting to get to that voltage. If you were to drop the voltage set-point from 28.8 to 24 (24V by the way = a dead lead-acid battery), you're most likely out of the regulation range on the high side if the AC power supply is set to 28.8, so the regulator will see the high voltage and try to fix that by dropping the output until it's not outputting at all.

Again, this is why I have to build a regulator for my system - it's more complicated than what the original voltage regulator was designed for, so it wouldn't be able to control the system properly.

Do you foresee any issues with the efficiency of the CVT in the system? Its going to cost you about 15% in engine output versus about 1-3% with a single speed toothed belt.

I do foresee some efficiency loss yes, even a belt drive with fixed sheaves shares a lot of the inefficiencies of a CVT, but the CVT adds a clutch (clutch slippage is a loss source) and the moving sheaves add another friction loss. Some of this can be overcome with a stiffer clutch (which I am planning to use) so there is no slip once engaged, other friction can be compensated for with the belt design - I am currently looking at Kevlar and stainless steel (like in automotive CVTs) belts which will reduce creep losses and seating/unseating losses as the belt goes around the two sheaves.

I'm hoping what I lose in efficiency by using the CVT versus the fixed ratio drive, I can gain back by being able to more precisely match the engine power output to the alternator power load. This would also give me the benefit of being able to give up efficiency for absolute power output. Remember I expect to actually need 450Amps for some instances, if I can't get there without adding another fixed ratio engine+alternator genset, that's an efficiency loss of another type and scale...

 

[90cummins]

tim29
I understand that the source with the higher voltage set-point will carry the load.
And in my case it is my N1603 @ 28.6v. What I'm asking is this; having reviewed the electrical diagrams for the N1603 can you see if it would be possible to adjust the output voltage with a potentiometer like they do with most of the MEP's.
If the answer is in your response forgive me for not understanding what you are saying.

90cummins

 

[tim292stro]

Please, just Tim.

As far as I have been able to read from the publically provided documentation (and the additional stuff you provided) there is no user-configurable settings on the N3211 regulator. Again as far as I can read, it will output 28.8V during operation. what I've been saying in my responses is that this is not a load-sharing regulator. In order to share a load, your other power source will have to watch how the regulator is controlling the alternator to determine how to drive itself. There is this tiny window (1-2V) of regulation, your other power source would have to understand how that regulator reacts to changes in the load and change its output to reflect the current conditions.

IMHO if you're really intending to load share, you may want to build your own regulator too.

I have the trouble shooting guide for the N1603-2 and the N3211 (attached).