Battery room ventilation plans

Bill SWF · January 2015

All, please let me know if you see any inherent flaws in this battery room design. The entire mechanical room for the PV solar system will be the battery room.

Attachment not found.

Attachment not found.

The mechanical room for the PV system gear and batteries is 4' x 11' x 9' tall with only exterior door. I have experience with building energy star houses that have to pass blower tests and realize the mechanical room has to be very airtight, especially at the ceiling level.

Passive ventilation consisting of a 4" PVC exhaust vent with the inlet in the ceiling centered over the batteries. The inlet is also a 4" PVC pipe that enters the room through the ceiling then extends downward ending about 6" above the floor.

There will also be a powered ventilation system that will consist of a 4" duct with the intake over the batteries at the ceiling with a 25 cfm inline exhaust fan. Looking at the Vents-US models: TT100, TT125 etc. These can be installed in series. I will still need to check the actual cfm allowing for the length of duct and elbows. I think that the Outback 8048A inverter will turn on a 120 volt circuit when battery charge reaches 80% or above. These fans are not rated for explosive atmosphere use, but from what I've read, since this system is designed to keep levels below the LEL, the fan does not have to be.

I came up with the 25 cfm by using the calculators at the links below for the largest battery system that I'm considering as an option, and came up with 25 cfm both times using the dimensions of the entire battery room.

http://www.sbsbattery.com/products-s...alculator.html

http://na.bhs1.com/battery-room/ventilation/

The room will have an H2 detector, most likely a Macurco GD 12 or an RKI PS2, with the sensor located on the ceiling over the batteries. The RKI PS2 has a remote sensor. I'm not sure if the Macurco does or not. The H2 detector will be set to turn on the first exhaust fan at 10% LEL and the second fan at 20% LEL. This system will have a backdraft damper. I would think it should be located at the intake end of the ductwork over the batteries. What I like about the Macurco is that it has a digital read out of the LEL %.

One string of batteries will sit on the floor in a 5" deep polypropylene containment pan. The second string will be on a shelf approx. 4' higher. This shelf does not run wall to wall, but has an opening at each end to allow the free movement of H2 up to the ceiling. I will fabricate a polypropylene cover for the plywood with a drip on the front and rear that extends downward to 1/2" below the 2x4 supports. I have run the numbers on the span of the 2x4s and the max load being carried. Not shown on the drawings is a 4" I beam mounted to the ceiling that will allow batteries to be lifted onto the upper shelf with a chain fall and trolley.

There will be plywood covers that can be installed over the near row of 4 batteries when working on the far row, such that one can lean their elbows on it. There will also be a walk board that can be installed at the appropriate height to stand on when service the upper level of batteries.

When the powered exhaust fan is operating, I would expect it to draw air from both the passive ceiling vent and also from the floor level passive vent.

Options being considered:

Installing a PVC drain in the containment pan that would drain the exterior with an inline valve. In the event of a spill, the electrolyte could be collected in a bucket outside. Any dirt that collected in the tray could likewise be rinsed out into a bucket outside.

What else?

I have attached pdf drawings of the mechanical room below. I've not posted attachments before so I hope I did this correctly.

Thanks,

Vic · January 2015

Re: Battery room ventilation plans

Bill,

Do not know all of the other constraints on your Power Room, but, personally, have placed two screened vents to the outside LOW in the power room -- one in the plywood Battery Box, and one LOW for the room. Then there is a larger ceiling vent flush with the surface of the ceiling material -- all passive.

One thought, is that for the most consistent battery temperature from the string on the floor, vs the one at four feet, that you try to get all of the batteries at the same elevation, not stacked. The power room might be Conditioned space, which should help reduce temperature variations from floor to ceiling, but, a reasonably large battery bank will need to rid itself of a few KW of waste heat generated on a full recharge from 75% (or so) State Of Charge.

With Inspectors around, you may need to use active ventilation for the room ... and so on. Opinions, Good Luck, Vic

BilljustBill · January 2015

Re: Battery room ventilation plans

I'm wondering what kind of climate you are in? With your experience in "Energy Star" construction, are there considerations of outside air venting inside when the extreme temps are seen on very hot and very cold days and weeks?

Would a vented battery box make your issues more simple?

I have the problem of Texas heat I have to contend with for both the battery storage area and the electronics in three controllers and two GTV3524 24v Outback inverters for an off grid system.

What works for you might also help me solve some problems are reasons I'm asking the above questions.

Vic · January 2015

Re: Battery room ventilation plans

Bill SWF,

Do you have a floor plan drawing of the Mechanical room (power room)? This might help us understand the layout of the batteries and the electronics.

This room is 11' long and 4' wide?

Since this room appears to be for the exclusive use as a power room, why would it need to be blower-tested?

Is there a plan to A/C this room? There will be a reasonable amount of heat resulting from charging the batteries, and form the electrical equipment operating in this room, that will probably need to be dealt with, Although there may be plans to use AGM batteries which are more efficient.

Is this power system connected to the Grid, or is it off-grid?
Thanks, Vic

waynefromnscanada · January 2015

Re: Battery room ventilation plans

Vic wrote: »

This room is 11' long and 4' wide?
Since this room appears to be for the exclusive use as a power room, why would it need to be blower-tested? Vic

Been wondering the same thing. Also about "Energy Star" houses. And the room being only 4 feet wide, with the batteries etc being against one wall, there may not be much room to move around or work on things unless one is thin and stays thin.

Bill SWF · January 2015

Re: Battery room ventilation plans

Vic,

Thanks.

Plans are the 2 links after the first sentence of the opening post.

I really don't have the room for both strings of batteries on the same level. But I will be printing out the info on the Outback 8048A Inverter and Outback FM80-150 Charge Controllers today. Outback seems to be really expanding the versatility of their gear. My system will have two charge controllers. I will be checking to see if they have the ability to use separate temp sensors for each of the 2 strings of batteries. In looking over one of their info sheets yesterday I noted that they are able to handle undersized generators and have the ability to charge battery banks of different voltages.

I am going to need to quantify the heat load from the gear and batteries and upsize the ventilation as needed. The line of fans that I mentioned can be installed in tandem in line, and each fan has a high and low speed. They are available in 4", 5", 6", 8"... So, I could easily install a line voltage T-stat to control one or both of the fans for ventilation (in addition to the H2 sensor being able to turn 1 fan on at alarm level 1 and the second on at level 2). The 25 cfm provides for a complete air change every 16 minutes, so I'm guessing that I would not have to bump that up too much more than double, but like I said, I do need to quantify this.

Blower door testing is just to achieve Energy Star rating for the entire residence. I really has little to do with the mech room specifically. I just mentioned it to say that I have experience with getting building shells pretty air tight, and will be able to do the same for the mech room.

The system is a hybrid grid tied system with battery backup. The AGM batteries that I looked at had pretty short warranties and the cost per AH was high. The 6 volt flooded RE batteries seemed to be the best value per AH and have longer warranties. So I'm trying to allow for a max battery system of two strings of 8 Rolls Surrette S-550 428 AH batteries.

BilljustBill,

I'm in central NC. Highs regularly in mid 90s in summer, with highs around 105 not all that unusual. I don't think the cold would be an issue with the mech room being part of the addition and being well insulated. Keeping the room cooled will be the harder task in a grid down situation in the summer. The PV system should provide enough heat itself in the winter, and the adjacent den will have a wood stove.

Wayne,

I will most likely increase the mech room by 8" in width, but some of the 8" will be eaten up by layer(s) of 5/8" fire rated sheetrock.

I am thin, and have only gone up an inch in waist size since college, and that was a very long time ago. Hell, the computer courses used punch cards.

All,

Thanks much for the input, it's much appreciated.

Bill SWF

BB. · January 2015

Re: Battery room ventilation plans

Give yourself room to work on the battery bank and electronics... And look at the size of batteries you will want to use. For larger systems, some folks will use fork lift batteries which can weigh 2,000 lbs or more for the "lead brick". Using a pallet jack, crane, etc. to move them around (concrete floor, no steps, some way to get it off a truck, etc.).

An 850 AH 24 volt forklift battery (2x 850 AH @ 24 volt battery bank minimum required for an 8 kWatt AC inverter running at full power) will weigh around 1,380 lbs, each. Regular 6/4/2 volt batteries in larger formats will weigh 100-300+ lbs each.

For flooded cell batteries, you may want them in their own room/box. They will vent a bit of electrolyte too (sulfuric acid mist)--You don't want to mix that with the electronics/other items (emergency supplies, extra storage, etc.).

AGM/Sealed batteries will not vent during normal operation--But towards end of life (and overcharging if there is a charge controller failure) still vent hydrogen and electrolyte mist--So venting is still needed for safety.

-Bill

Bill SWF · January 2015

Re: Battery room ventilation plans

BB. wrote: »

Give yourself room to work on the battery bank and electronics... And look at the size of batteries you will want to use. For larger systems, some folks will use fork lift batteries which can weigh 2,000 lbs or more for the "lead brick". Using a pallet jack, crane, etc. to move them around (concrete floor, no steps, some way to get it off a truck, etc.).

An 850 AH 24 volt forklift battery (2x 850 AH @ 24 volt battery bank minimum required for an 8 kWatt AC inverter running at full power) will weigh around 1,380 lbs, each. Regular 6/4/2 volt batteries in larger formats will weigh 100-300+ lbs each.

For flooded cell batteries, you may want them in their own room/box. They will vent a bit of electrolyte too (sulfuric acid mist)--You don't want to mix that with the electronics/other items (emergency supplies, extra storage, etc.).

The drawing shows the required 3' x 3' work space (square box with diagonal X) in front of the panels and inverters.

AGM/Sealed batteries will not vent during normal operation--But towards end of life (and overcharging if there is a charge controller failure) still vent hydrogen and electrolyte mist--So venting is still needed for safety.

-Bill

Bill,

I worked off the physically largest battery system that I was considering, which was 2 strings of 8 Surrette 6 volt 428 AH flooded lead acid batteries. About 130 lbs each I think. I'll have a short length of 4" I beam mounted to the ceiling with trolley and chain fall to lift them to the upper shelf.

The plan shows the required 3' x 3' working area in front of the panels and inverter/charge controller.

No other storage in the room, just the inverter, chargers, and electric panels. I guess I should consider at least a curtain to contain the mist, but it would have to stop short of the ceiling to prevent creating a potential pocket of H2 that would not be vented.

Thanks,

Bill SWF

BB. · January 2015

Re: Battery room ventilation plans

Bill,

You may also want to look at Water Miser Battery Caps... NAWS sells a low or medium height (I am not sure), but there are also tall versions. They offer more internal surface area to collect the mist droplets--A bit less escapes and does noticeably reduce distilled water usage.

http://www.flowsystemsusa.com/water-miser-vent-cap.html

I don't know if the taller versions are "worth the size/cost" (at least one person here suggested it was)--Perhaps NAWS can special order the taller units (if you have room on top of the battery).

There are Hydro Caps with some sort of catalyst inside (palladium/platinum or similar) that also catalyze the Hydrogen+Oxygen back into water.

Hydrocap | Information - Hydrocap Corp

They are much more expensive (many times more expensive) and have a definite life (basically, the more you equalize/gas your battery bank, the shorter the life of the catalyst. These are usually NOT worth the costs/issues (for example, you need to remove the Hydrocaps when equalizing because they can overheat with lots of Hydrogen gas being catalyzed).

-Bill

Bill SWF · January 2015

Re: Battery room ventilation plans

Got the Water Miser Caps on my list. The extra tall are available from the manufacturer if not from NAW. I'll have at least 2' of space over the lower set of batteries and more than that over the upper set.

The Water Miser Caps sound like they are definitely worth the cost.

Thanks,

Bill SWF

Vic · January 2015

Re: Battery room ventilation plans

Hi Bill SWF,

Thanks for the Plan view of the room, and the system is Hybrid GT.

Recharging batteries that are cycled daily can cause considerable battery heating. For the Hybrid GT, probably less heating occurs. In your type system, the batteries are "worked", by them supplying peak current on each half of the sine wave peak. This working also causes heating, that depends on the impedance of the batteries, would expect.

Yes, as BB Bill mentioned, having space around the batteries, making it very easy to check their SG and electrolyte levels, and fill the cells as required usually means that the batteries will actually be checked and maintained -- this is very important with Flooded batteries. I would not appreciate ONLY two foot headroom above the tops of the lower battery bank when servicing the Flooded batteries here. Seems far too restrictive, in my mind. Too bad that you cannot make that power room larger. Here on power room is a cut off cargo container -- 10' long X 8' X 8'. This is a fine size for what we need to do, and allows a single layer of batteries, that sit in an insulated plywood battery box, with a hinged lid that is now NEVER closed (for optimum battery cooling.

Regarding any temperature differential from having batteries stacked vertically, having two RTSes -- one on each FM CC -- might be supported, BUT, since each battery string is really connected in parallel (at the inverter, at least), individual CCs will not be able to use its temperature-corrected proper charge voltage.

GT systems often use different charging strategies, than off-grid systems, so any temperature effects on battery voltage might not be too much of a negative.

You might want to plan on a small Air Conditioner for that room, IMO. Or, at least, some positive forced circulation of air, perhaps only at night. As you probably know, for each 10 degrees C rise in battery temperature above about 25 C, battery lifespan is halved. On Summer days, if is easy for power rooms to experience a greater than 10 C rise over 25 degrees C.

FWIW, Have Fun, Vic

BB. · January 2015

Re: Battery room ventilation plans

Just to give yourself some idea of heating loads... Typical worst case lead acid battery efficiency is around 80% (loses between discharging and recharging), roughly 95% efficiency for the MPPT charge controller and around 85% typical efficiency for the Inverter-charger.

So, during parts of the day, you could be looking at several kWatts of heating (controllers, inverters, battery bank) pretty easily.

You did not give details for your system:

6 kWatt array * 0.05 inverter losses = 300 Watts from charge controller
6 kWatt into battery bank * 0.20 loss = 1,200 Watts "cycling battery bank"
4 kWatt from AC inverter * 0.15 loss = 600 Watts AC inverter

2,100 Watts of heat into work space in middle of day....

Just a rough estimate, your numbers will vary (lead acid batteries are >90% efficient when less than 80% charged, and become less efficient the higher the state of charge.

Also, many of the pieces of equipment can be quite noisy (cooling fans, 120 Hz from transformers/switching gear/wiring)--The room behind the power room wall should either be well insulated (such as staggered 2x4/2x6 studs to reduce sound transmission, insulation, heavy sheet rock, etc.) between power room and living space. Possibly mounting "noisy" gear on outside wall rather than interior wall (especially if office/bedroom/living room where you want quite).

Personally, I am always a bit scared of fire with large battery banks and the "open" wiring that some folks use when wiring up solar (vs metal trays and conduit). Using approved fire resistant materials on walls/floors, possibly cement board behind electrical equipment/wiring and non-flammable tile on floors, etc.

-Bill

Bill SWF · January 2015

Re: Battery room ventilation plans

Vic, thanks.

All good info.

The floor level batteries would be serviced kneeling. To work on the far row, the plywood shelf would be placed above the near row allowing me to rest my elbows there as needed. Not perfect, but a lot easier than most of the regular maintenance on my trucks, tractor, etc.

I am thinking about a buried PVC pipe to draw ventilation air through in the summer. I'll have the line item budget for the entire project done in about a week or so, and if the budget allows, maybe an 8x8 or so detached battery room. Since it would seem that cooling will be more important than keeping the batteries warm in this climate, my first thoughts are to berm the detached battery room on 3 sides.

Thanks,

Bill SWF

Bill SWF · January 2015

Re: Battery room ventilation plans

BB,

This is where I'm at right now.

24 Solar World 280 watt modules, 3 panels per string, 8 strings (4 strings per controller)

Outback GS8048A; Outback GSLC; 2 - Outback FM80-150 Charge Controllers

Trojan L16HG-AC; 6 volt 435 AH at 20 hrs; Two strings of 8
6.85 x 12.25 x 16.41; 1200 cycles at 50% dod; 3500 cycles at 20% dod

Gotcha on the noise. Would most of the noise be daylight hours?

Re open wiring, all the wiring in both our barns is all in conduit. I would use oversized EMT or possibly a trough where and as needed in the mech room for the DC conductors. (As well as conduit for the AC circuits.) I have been thinking about the DC circuits and was thinking that it would be a good idea to locate overcurrent protection as close as possible to each of the two strings of batteries.

Thank you for your input.

Bill SWF

BB. · January 2015

Re: Battery room ventilation plans

Bill,

You got it right regarding trays/conduit/DC circuit protection.

Noise, yes, the Outback (and some other brands/models) solar charge controller can be a bit on the noisy side. However, some folks have complained about 120 Hz noise from their AC inverters too (I do not know anything about the Outback Radian and its possible noise, or not).

Sizing the array to the battery bank size (5% to 13% or so rate of charge rule of thumb for solar array sizing):

870 AH battery bank * 59 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 3,333 Watt array minimum
870 AH battery bank * 59 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 6,666 Watt array nominal
870 AH battery bank * 59 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 8.666 Watt array "cost effective" maximum

24 * 280 Watt panels = 6,720 Watt array

You look to have a pretty nominal system using our various rules of thumb.

Cooling--Some folks have buried many feet of plastic pipe for cool/dry air (need to drain pipe if you have humidity above the dew point of the average ground temperature--But I am not sure how useful that would be.

If you discharge the battery bank by 25% per day nominal (2 days storage, 50% maximum discharge):

870 AH * 48 volts discharging * 0.85 inverter eff * 1/2 days storage * 0.50 maximum discharge = 8,874 WH per day of stored AC power

Using PV Watts for Raleigh NC, fixed array tilted to 36 degrees:

Month
Solar Radiation
(kWh/m²/day)

1
3.73

2
4.66

3
5.38

4
5.76

5
5.55

6
5.77

7
5.53

8
5.58

9
5.35

10
5.33

11
4.34

12
3.51

Year
5.04

And if you toss the "bottom three months" of winter, your average "typical weather" amount of sun for February from solar would be:

6720 Watt array * 0.52 end to end system eff * 4.66 hours of sun "break even February" = 16,284 WH = 16.3 kWH average in February

Does this look like a reasonable amount of power for your needs?

You have a genset for backup power (generator/fuel in separate building from home/other buildings--For fire protection just in case)?

-Bill

Bill SWF · January 2015

Re: Battery room ventilation plans

16.3 kWH per day x 30 Days = 489 kWH in a month.

Our bill for last Feb shows 1,142 kWH used. That's heating with a heat a heat pump. The new addition will have a wood stove that will heat the whole house if I just run the AHU blower on "circulate" (very low speed). Wood shed is already filled with a 2.5 year supply. We were expecting to cut the electric bill about in half. And be able to get by in an extended power outage by cutting electric usage drastically.

I ran this calculator at 40 degrees (10/12 roof pitch) and orientation of 30 degrees east of due south (150 rather than 180, right?) and got acceptable numbers.

I can run about 150' of pipe downslope such it can drain to daylight so the condensation can drain. With a vertical section of pipe for air intake.

6,500 w diesel generator and a manual well pump alongside our deep well electric pump. The brochure for the Outback 8048A states that it will work with undersized generators.

Bill SWF

BB. · January 2015

Re: Battery room ventilation plans

Sounds good. Study up on generator support. That can be very helpful (run a smallish genset, and the inverter can help with surge/heavy loads that exceed the generator capacity).

You might have to call Outback to get the latest details. Generator Support does not always make it from the marketing document to the shipping product.

Demonstration of Generator Support

-Bill

Bill SWF · January 2015

Re: Battery room ventilation plans

BB,

That's a great link. I've found that the newest updates don't always make it to all the tech support folks either.

I think the Outback 8048A has a lot of these advanced features as well as the ability to download upgrades. I'll be wading through the manuals over the next couple weeks.

Bill SWF

HiAltitude · July 2015

BB. wrote: »

Re: Battery room ventilation plans

Bill,

You may also want to look at Water Miser Battery Caps... NAWS sells a low or medium height (I am not sure), but there are also tall versions. They offer more internal surface area to collect the mist droplets--A bit less escapes and does noticeably reduce distilled water usage.

http://www.flowsystemsusa.com/water-miser-vent-cap.html

I don't know if the taller versions are "worth the size/cost" (at least one person here suggested it was)--Perhaps NAWS can special order the taller units (if you have room on top of the battery).

-Bill

BB, thanks for the reference to the water miser caps.

I'm interested in the taller Water Miser caps for my application, but I'm wondering if others on the forum have any experience with the taller caps, regarding checking SG, checking water levels, and adding water. I'm wondering if these are any more restrictive than their shorter versions.

thanks.

HA

vtmaps · July 2015

HiAltitude wrote: »

I'm interested in the taller Water Miser caps for my application, but I'm wondering if others on the forum have any experience with the taller caps, regarding checking SG, checking water levels, and adding water. I'm wondering if these are any more restrictive than their shorter versions.

I ordered the tall caps direct from the manufacturer. No problem checking SG. To check electrolyte level and add water I remove the water misers because if I leave them in place and just lift up their hinged tops I can't see well enough down through them.

Actually, I can check the electrolyte level with the caps in place... if my hydrometer sucks a bit of air, then the level is low and I need to add water, but to add water I like to see what I am doing so I remove the water misers.

When I add water, I usually do it midway through absorb. First I set the controller to float so the cells are not gassing while I check, then I add water, then I replace the caps and go back into absorb to stir up the electrolyte.

--vtMaps

Vic · July 2015

Not to be too argumentative, however, I have noticed no reduction in water use with the standard height Water Miser caps, and do believe that they actually may cause more escape of electrolyte, based on the pooling and weeping of electrolyte on the top of the batteries where they are in use. The standard OE caps did not weep or splatter/spatter at all.

This electrolyte escape does not occur until the caps have been in use for some time. And ONLY rinse the WM caps when they begin to weep electrolyte, or when they begin to "whistle" during gassing.

The only reason that I used them on the battery bank that uses them on every vent, was that that battery bank needed to be moved using a Hand-Truck. The WMs DO result is essentially no electrolyte spillage when the(se) batteries are tipped when hand trucking them.

Will say that the above references batteries with a relatively large Electrolyte Reserve (space above the plates), and perhaps batteries with less space above the plates might possibly benefit from WMs. But would bet that the WMs would still load with electrolyte that would weep (IMO).

And, it is difficult to believe that WM caps "Nearly Eliminate Need For Equalization", or would "Reduce Watering Intervals by 50 - 60%, as stated.

Just my experience with standard-height WM caps. FWIW, Vic

HiAltitude · July 2015

vtmaps wrote: »

Actually, I can check the electrolyte level with the caps in place... if my hydrometer sucks a bit of air, then the level is low and I need to add water, but to add water I like to see what I am doing so I remove the water misers.

When I add water, I usually do it midway through absorb. First I set the controller to float so the cells are not gassing while I check, then I add water, then I replace the caps and go back into absorb to stir up the electrolyte.

--vtMaps

Thanks, these are both great ideas. That's a great way to mix up that added water,

HiAltitude · July 2015

BB. wrote: »

Re: Battery room ventilation plans

Bill,

Sizing the array to the battery bank size (5% to 13% or so rate of charge rule of thumb for solar array sizing):
870 AH battery bank * 59 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 3,333 Watt array minimum

870 AH battery bank * 59 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 6,666 Watt array nominal

870 AH battery bank * 59 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 8.666 Watt array "cost effective" maximum

24 * 280 Watt panels = 6,720 Watt array

You look to have a pretty nominal system using our various rules of thumb.

Cooling--Some folks have buried many feet of plastic pipe for cool/dry air (need to drain pipe if you have humidity above the dew point of the average ground temperature--But I am not sure how useful that would be.

If you discharge the battery bank by 25% per day nominal (2 days storage, 50% maximum discharge):

870 AH * 48 volts discharging * 0.85 inverter eff * 1/2 days storage * 0.50 maximum discharge = 8,874 WH per day of stored AC power

You have a genset for backup power (generator/fuel in separate building from home/other buildings--For fire protection just in case)?

-Bill

Hi Bill, I very much appreciate the "rules of thumb" calculations you used above.

I'm new to the forum, and may not have seen this, but do you have a similar calculation for suggested generator size in watts?
I would expect that it would be related to the C rate in amps required by the battery over some period of time

thanks for your time. GP.

vtmaps · July 2015

HiAltitude wrote: »

I'm new to the forum, and may not have seen this, but do you have a similar calculation for suggested generator size in watts?
I would expect that it would be related to the C rate in amps required by the battery over some period of time

Can't calculate a generator size without knowing the loads. If the only load is battery charging, that's one thing. Are you running the laundry, power tools, well pump, etc while you are charging the batteries? Some folks have two generators... one for battery charging and a larger one for tools or other large loads.

Another consideration is how long you want it to take to charge the batteries. In the summer I throttle down the charge rate (takes longer to charge the batteries) because I don't want to create heat. In the winter I use a higher charge rate because I do want to heat up the batteries (my battery box is in a building that is about 35-40° F in the winter).

Finally, there is the type of generator to consider. Inverter generators, when used at less than full capacity are much more efficient than conventional generators, but at full capacity a conventional generator is usually a bit more efficient than an inverter generator.

And what does "full capacity" mean? That's another story... prime generators can run at their full rated capacity indefinitely. Other generators will last longer if they run at less than full rated capacity.

--vtMaps

Edit: This thread is all over the place... ventilation, battery caps, generators... if you want to change the subject, don't be afraid to start a new thread.

HiAltitude · July 2015

VTMaps. Thanks for the additional considerations and the seasonal optimization of the charge rate. 'Copy on finding or starting an appropriate thread.

Battery room ventilation plans

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