Reply
 
Thread Tools Display Modes
 
Old 07-15-2019, 06:39 PM   #1
Almost There
 
Join Date: Dec 2018
Location: NW Montana
Posts: 69
Year: 2002
Engine: T444E/Allison 2000
AH Battery help URGENT

Hey all!

Working on my solar (no clue what I'm doing lol) I have 2 100w mono panels from renogy and plan on adding 2 more. I am just about to buy 2 100ah sized batteries and also considering adding 2 more. My question is if you want to basically match the solar wattage to the ah. 2 100w panels 2 100ah batteries, 4 100w panels 4 100 ah batteries and so on. I have done my power audit and attached it, any help is really really appreciated as I am in way over my head hahah!

Thanks,

Kevin
Attached Images
File Type: jpg Screenshot 2019-07-15 at 5.37.10 PM.jpg (156.0 KB, 37 views)
KevinDarcy11 is offline   Reply With Quote
Old 07-15-2019, 07:59 PM   #2
Bus Crazy
 
roach711's Avatar
 
Join Date: May 2010
Location: Farmington Hills, Mi (Detroit area)
Posts: 1,844
Year: 2000
Coachwork: Eldorado Aerotech 24'
Chassis: Ford E-450 Cutaway Bus
Engine: 7.3L Powerstroke
Rated Cap: 19
100 amp hours at 12 volts equals 1200 watts capacity per battery. Ideally you only discharge your house batteries to 50% so you'd need 600 watts per battery to recharge the bank. Assuming full solar panel output it would take 6 hours to recharge the bank. I'm sure that in the real world it would take a bit longer.

From what I've read, you want to match your converter/charger charging amps to the size of the battery bank.

I'm sure someone with more solar experience will chime in.
__________________
The Roach Motel
roach711 is offline   Reply With Quote
Old 07-15-2019, 08:04 PM   #3
Bus Nut
 
CMORGANSKOOL's Avatar
 
Join Date: Aug 2018
Location: Philadelpiha Pennsylvania
Posts: 344
Year: 2007
Coachwork: IC
Chassis: FE Bus
Engine: DT-466 7.6L Turbo Diesel
Rated Cap: 77
You want way more solar than it takes to charge the battery bank and way more battery than you need to power the expected loads. I would triple the battery you think you need and try and squeeze as much solar as you can afford. Always over engineer because you will be much happier having the power and not needing it than to not have it and need it or fry a battery bank because you over depleted it. On my build I'm slowly piecing together 1000ah of agm batteries and would like 2000watts of solar, but based off my recommendation to you I should have 5000 watts. You can only afford what you can afford. Remember you can always charge your batteries off a generator if you don't have enough panels or the weather is bad for long periods.
CMORGANSKOOL is offline   Reply With Quote
Old 07-15-2019, 10:55 PM   #4
Mini-Skoolie
 
Join Date: Mar 2018
Posts: 39
Hello Kevin. I'm a former Vermonter - what a great state! I'd love to add some useful input here. I took a look at your table, and I'm suspicious of some of the numbers. This will make a BIG difference to your final design. Does your fridge really consume 89Watts all the time? I have a 120V dorm style fridge (slightly larger) that averages 13 watts. If you have your fridge available you might want to plug it into a Kill-O-Watt meter to see what its average watt rating is. Are you really going to run two different 1300 watt induction units for 3 hours each per day? And will they actually be on high for the entire 3 hours? The real number here is a really big deal!! And does your water pump really consume 250 watts? That might be true. But will the pump actually be running for 3 solid hours a day? Keep in mind that many loads with a certain amperage or watt rating will actually average far less than that rated wattage. A fridge probably doesn't run 100% of the time. An induction burner probably isn't on high for 100% of the time, etc.

And the other part of solar is what are the worst case conditions that this will need to run in? Vermont in the winter? Somewhere else in the winter? And are you going to have any other charging source? There are some slick ways to charge from your bus alternator (with some caution...). These things will affect both solar panel size and battery requirements. Hopefully these questions aren't overwhelming.... I'd love to toss in my two cents worth if you are able to just verify these details.
glenncooper is offline   Reply With Quote
Old 07-15-2019, 11:28 PM   #5
Almost There
 
Join Date: Dec 2018
Location: NW Montana
Posts: 69
Year: 2002
Engine: T444E/Allison 2000
Quote:
Originally Posted by glenncooper View Post
Hello Kevin. I'm a former Vermonter - what a great state! I'd love to add some useful input here. I took a look at your table, and I'm suspicious of some of the numbers. This will make a BIG difference to your final design. Does your fridge really consume 89Watts all the time? I have a 120V dorm style fridge (slightly larger) that averages 13 watts. If you have your fridge available you might want to plug it into a Kill-O-Watt meter to see what its average watt rating is. Are you really going to run two different 1300 watt induction units for 3 hours each per day? And will they actually be on high for the entire 3 hours? The real number here is a really big deal!! And does your water pump really consume 250 watts? That might be true. But will the pump actually be running for 3 solid hours a day? Keep in mind that many loads with a certain amperage or watt rating will actually average far less than that rated wattage. A fridge probably doesn't run 100% of the time. An induction burner probably isn't on high for 100% of the time, etc.

And the other part of solar is what are the worst case conditions that this will need to run in? Vermont in the winter? Somewhere else in the winter? And are you going to have any other charging source? There are some slick ways to charge from your bus alternator (with some caution...). These things will affect both solar panel size and battery requirements. Hopefully these questions aren't overwhelming.... I'd love to toss in my two cents worth if you are able to just verify these details.
Glenn! Thanks for the reply. The fridge I'm going to run is the Mr Buddy 63 quart fridge and only draws .74 amps/hour. I'm thinking about nixing the induction burners and just working off propane. I'd like to do the burners but I also don't want to kill my reserves running them. My wife and I love to cook so I was definitely over estimating numbers with that. As far as the water pump I think we are just going to switch to a foot pump for the time being.

So worst case scenario are winters in Montana. We just moved back to Montana and the winters are similar to VT. They can get pretty dark and dreary so I was definitely thinking of doing something off the alternator. Any recommendations on isolators and how much ah I would need with the energy audit I did?

Thank you so much for your help, it's really really appreciated!!!

Best,

Kevin
KevinDarcy11 is offline   Reply With Quote
Old 07-16-2019, 12:54 AM   #6
Mini-Skoolie
 
Join Date: Mar 2018
Posts: 39
Kevin. Thanks for that additional information. So the fridge is drawing 8.9 watts, not 89 watts. If you are doing a lot of cooking then electric cooking isn't a great option. I don't think you need to toss out the electric water pump. I did some calculations with a 250 watt pump running 1 hour per day which still seems too high. Your original numbers had 9000WH per day. Dumping the electric cooking and correcting the fridge brought this down to 1155 KWH per day. You didn't mention if your batteries were going to be AGM or Lithium. It is safe to draw AGM batteries down to about 50% of charge. Lithium can be drawn down to about 20% of charge. This makes a big difference on available power. The size of the solar system relative to the batteries can vary all over the place based on the environment the solar will run in. Montana winters will be an incredible challenge, and depending on how cloudy it is where you are I doubt that even a large solar system would handle your load. So putting some numbers on it: I would be thinking about 400 ah of batteries. If these were AGM then you have 200 ah available which is 2400 watt-hours available (200 * 12). That's enough to run you for 2 days - that's pretty marginal. I would probably be thinking about 400 watts of solar if you can fit it. If you estimate that you average 3 hours equivalent sun each day in the winter then this gives you 1200 watt-hours of energy per day, which just barely meets your electric needs of 1154 watt-hours per day. Of course if you get many days of cloudy weather then you're toast. As far as getting juice from the alternator, I can share these thoughts: There are a lot of ways to use a massive relay to connect your house batteries to the bus charging system whenever the alternator is on. This would allow massive charging currents to your batteries. But this massive charging current won't be good for your batteries over time, and might destroy your alternator. I'm not that familiar with bus alternators (vs. van alternators), but in my van the alternator has a duty cycle, so that even if it's a 175 amp alternator it can't put that out for an hour straight. the devices that tie these together are called Battery combiners. Again - many of these are basically a big relay. I bought a Magnum ME-SBC smart battery combiner. This charges at 25 amps. It's a great solution for me where I have smaller batteries and will be driving for many hours most days, but with your larger batteries and possibly less engine-on time you'll need more current. I thought I saw someone with a 60 amp unit, but I don't know where that was. If you're going to be near a power source in Montana then buying an inverter/charger combination is a great choice.
glenncooper is offline   Reply With Quote
Old 07-16-2019, 08:09 AM   #7
Almost There
 
Join Date: Dec 2018
Location: NW Montana
Posts: 69
Year: 2002
Engine: T444E/Allison 2000
Quote:
Originally Posted by glenncooper View Post
Kevin. Thanks for that additional information. So the fridge is drawing 8.9 watts, not 89 watts. If you are doing a lot of cooking then electric cooking isn't a great option. I don't think you need to toss out the electric water pump. I did some calculations with a 250 watt pump running 1 hour per day which still seems too high. Your original numbers had 9000WH per day. Dumping the electric cooking and correcting the fridge brought this down to 1155 KWH per day. You didn't mention if your batteries were going to be AGM or Lithium. It is safe to draw AGM batteries down to about 50% of charge. Lithium can be drawn down to about 20% of charge. This makes a big difference on available power. The size of the solar system relative to the batteries can vary all over the place based on the environment the solar will run in. Montana winters will be an incredible challenge, and depending on how cloudy it is where you are I doubt that even a large solar system would handle your load. So putting some numbers on it: I would be thinking about 400 ah of batteries. If these were AGM then you have 200 ah available which is 2400 watt-hours available (200 * 12). That's enough to run you for 2 days - that's pretty marginal. I would probably be thinking about 400 watts of solar if you can fit it. If you estimate that you average 3 hours equivalent sun each day in the winter then this gives you 1200 watt-hours of energy per day, which just barely meets your electric needs of 1154 watt-hours per day. Of course if you get many days of cloudy weather then you're toast. As far as getting juice from the alternator, I can share these thoughts: There are a lot of ways to use a massive relay to connect your house batteries to the bus charging system whenever the alternator is on. This would allow massive charging currents to your batteries. But this massive charging current won't be good for your batteries over time, and might destroy your alternator. I'm not that familiar with bus alternators (vs. van alternators), but in my van the alternator has a duty cycle, so that even if it's a 175 amp alternator it can't put that out for an hour straight. the devices that tie these together are called Battery combiners. Again - many of these are basically a big relay. I bought a Magnum ME-SBC smart battery combiner. This charges at 25 amps. It's a great solution for me where I have smaller batteries and will be driving for many hours most days, but with your larger batteries and possibly less engine-on time you'll need more current. I thought I saw someone with a 60 amp unit, but I don't know where that was. If you're going to be near a power source in Montana then buying an inverter/charger combination is a great choice.

Wow, thank you for all the help! We will be running AGM. I have two on the way and will be adding two more. I have 2 solar panels and will be adding two more as well. Final setup before winter hits should be 400w solar and 400ah. As far as charging is concerned, I read somewhere about what you are talking about. It sounded like charging off the alt gave a huge burst of energy which can be good on the front end but then needs to be slowly charged from solar as a trickle? Is a battery combiner the same thing as an isolator?

Thanks again for all the great info!

Best,

Kevin
KevinDarcy11 is offline   Reply With Quote
Old 07-16-2019, 08:12 AM   #8
Mini-Skoolie
 
Join Date: Mar 2018
Posts: 39
Some of the things called battery combiners are isolators. The idea is the same. When the vehicle is running to tie the battery sets together. But when the vehicle is off you isolate so that the house batteries don't drain the starting batteries. Either of these devices won't top off the battery completely, will get close. That's where the secondary system comes in - an inverter/charger or solar charger. These will top off the batteries.
glenncooper is offline   Reply With Quote
Old 07-17-2019, 05:40 PM   #9
Skoolie
 
bubb, the real one's Avatar
 
Join Date: Dec 2014
Location: central texas
Posts: 125
Year: 1990
Coachwork: Thomas/International
Chassis: 3700
Engine: 7.3
Rated Cap: 72
just the burner

If I see the chart correctly, I see your burner takes 11amps AC to run, this means it will pull 110 amps of Dc to run, one amp AC equals about 10 amps DC, I have not even gotten into the ~20% of you power that will be lost between the panels/wires/connectors/inverters/etx.



The max power you can pull from a battery and not have the voltage drop significantly is about supposedly about 10% of its AH capacity, this means you can only pull about 10 amps from a 100ah battery, but from personal experience with my batteries pulling 10% will only last a few minutes before the battery voltage drops below 11v and the inverter shuts down.


Another limit of lead acid batteries is that you can only charge them with up to about 10% of their AH capacity on a regular basis before you start to age them so you would only want to put about 10 amps of solar per 100ah battery, as measured at the battery post.



Since you live up north and the sun will be low in the horizon you will probably want 300 to 400 watts of solar per battery, to max your charging ability but this depends upon the tilt of the panel and any trees in the way.
__________________
my bus thread, http://www.skoolie.net/forums/showthread.php?t=8860&highlight=bubb
bubb, the real one is offline   Reply With Quote
Old 07-18-2019, 08:08 PM   #10
Almost There
 
Join Date: Dec 2018
Location: NW Montana
Posts: 69
Year: 2002
Engine: T444E/Allison 2000
Quote:
Originally Posted by bubb, the real one View Post
If I see the chart correctly, I see your burner takes 11amps AC to run, this means it will pull 110 amps of Dc to run, one amp AC equals about 10 amps DC, I have not even gotten into the ~20% of you power that will be lost between the panels/wires/connectors/inverters/etx.



The max power you can pull from a battery and not have the voltage drop significantly is about supposedly about 10% of its AH capacity, this means you can only pull about 10 amps from a 100ah battery, but from personal experience with my batteries pulling 10% will only last a few minutes before the battery voltage drops below 11v and the inverter shuts down.


Another limit of lead acid batteries is that you can only charge them with up to about 10% of their AH capacity on a regular basis before you start to age them so you would only want to put about 10 amps of solar per 100ah battery, as measured at the battery post.



Since you live up north and the sun will be low in the horizon you will probably want 300 to 400 watts of solar per battery, to max your charging ability but this depends upon the tilt of the panel and any trees in the way.
Man that's going to be tough... We decided to nix the electric burners and just run propane for cooking. Not a big deal. All we can really afford are the 100ah batteries. Money is definitely tight so hopefully there's a way to make this work... I am setting up the system with 2 100w panels and 2 100ah batteries but got a 40 controller and plan on adding the other 2 panels and 2 batteries in the next few months. Even if we just have enough power to run led lights and do some light electronics charging we will be happy. We don't really watch TV or anything. Gotta get the wood stove in ASAP as well before the snow comes
KevinDarcy11 is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


» Featured Campgrounds

Reviews provided by

Powered by vBadvanced CMPS v3.2.3

All times are GMT -5. The time now is 01:33 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2019, vBulletin Solutions, Inc.