# Help with basic portable generator

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Registered Users Posts: 8
I'm a newbie to solar but setup a basic small system with a 120ah battery and
1000w inverter and 100amp solar panel. The solar panel charges the battery in about 12 hours after it gets down to about 60%.

My question is can I keep charging the battery with the solar panel while running appliances through the inverter. There is a 20A Charge Controller built into the solar panels.. I tried connecting the solar panel while the inverter was on and it created a huge spark (pretty dumb i know).

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Re: Help with basic portable generator
tyankee wrote: »
I'm a newbie to solar but setup a basic small system with a 120ah battery and
1000w inverter and 100amp solar panel. The solar panel charges the battery in about 12 hours after it gets down to about 60%.

Welcome to the forum T.Yankee!

Solar is really all about the numbers and some basic math. And the "units".

I would guess that is a 100 Watt "12 volt panel"--Can you confirm that Vmp is around 17.5 to 18.6 volts or so? That is usually the "optimum" voltage for a solar panel on a 12 volt battery bank with a PWM charge controller.

If all is working well, you would expect in full noon time sun around:

100 Watts / 17.5 volts = 5.7 Amps

...of charging current.

If you discharge your battery bank by ~40% depth of discharge (60% state of charge):

120 AH * 0.40 discharge = 48 AH of discharge.

48 AH * 1.10 battery eff * 1/5.7 amps full sun = 9.3 Hours of full sun charging
9.3 hours of full sun / ~5 hours of full sun in sunny summer weather = ~1.8 days of charging in summer
My question is can I keep charging the battery with the solar panel while running appliances through the inverter.

And here is the problem... A 1,000 Watt AC inverter--If the battery could power it would only last:

120 AH * 12 volts * 0.85 inverter eff * 1/1,000 Watt AC load = 1.224 hours = 1h 13 minutes

A decent AGM battery could sustain ~C*1 discharge (discharge to dead) -- But unless you are running power tools (or other loads that only operate for very sort times), a 1,000 Watt AC inverter on this small of battery is usually way over-sized for most people.
There is a 20A Charge Controller built into the solar panels.. I tried connecting the solar panel while the inverter was on and it created a huge spark (pretty dumb i know).

Facing the solar array from the sun/covering with dark material to "turn the panel off" is handy. If you connect the panel backwards directly the the battery--You can easily "fry" the panel (connecting panels backwards will be a dead short on a battery bank).

If you are connecting to the solar panel input on a solar charge controller--Connecting backwards should not damage panels, and many controllers are protected against reverse polarity (not all--Don't know about yours).

A 100 watt panel with 120 AH battery bank is about the minimum rate of charge we would recommend (120 AH * 5% minimum rate of charge = 6 amps minimum recommended rate of charge).

We really like to start with your loads--And design a system to support your needs... Of course we can start backwards--You have a battery (or solar panel) and what could the system power that would be useful to you.

More or less, a 10 amp @ 12 VDC or ~120 Watt load would be a more "reasonable" load for your system (i.e., emergency power).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 8
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Re: Help with basic portable generator

Darn, i didn't understand most of that.. I'm really a newbie.. One thing i CAN say is that i hooked up my computer, 2 printers, model, phone, and small fan to the inverter and they all ran for about 8 - 16 hours before the battery died overnight.. Here are the specs i received with the unit (it came as a package from GEOKING):

Technical Features

120 watts solar panels 2x60 watts
15 Amps Solar charger controller
100 Amh Battery storage (1200 watts)
1000 watts continues running power invert
4 receptacles outlets 120 AC volts
2 12 volts cigarette type connections

Power inverter Modified sine wave

Energizer 1000W DC to AC inverter
Continuous output power 1000W
DC voltage input 11-Volt DC to 15.5-Volt DC
Full output load capacity is available instantly
High and low input voltage alarm and shut-down
Overload and short circuit protection and shut down
Internal cooling fan
Digital display of output voltage
Multiple AC output sockets; mounted on top of inverter for convenience

Folding Solar Panels
- 2 x 60 watts polycrystalline
- Voc: 21.60V- Isc: 7.72 amp
- Vmp: 17.30V- Imp: 6.94 amp

Solar charger controller
- Geoking Solar 12/24 V 10 AMP
- PWM charging mode
- Low Voltage reconnect
- Build-in electronic fused
- General switch
BB. wrote: »
Welcome to the forum T.Yankee!

Solar is really all about the numbers and some basic math. And the "units".

I would guess that is a 100 Watt "12 volt panel"--Can you confirm that Vmp is around 17.5 to 18.6 volts or so? That is usually the "optimum" voltage for a solar panel on a 12 volt battery bank with a PWM charge controller.

If all is working well, you would expect in full noon time sun around:

100 Watts / 17.5 volts = 5.7 Amps

...of charging current.

If you discharge your battery bank by ~40% depth of discharge (60% state of charge):

120 AH * 0.40 discharge = 48 AH of discharge.

48 AH * 1.10 battery eff * 1/5.7 amps full sun = 9.3 Hours of full sun charging
9.3 hours of full sun / ~5 hours of full sun in sunny summer weather = ~1.8 days of charging in summer

And here is the problem... A 1,000 Watt AC inverter--If the battery could power it would only last:

120 AH * 12 volts * 0.85 inverter eff * 1/1,000 Watt AC load = 1.224 hours = 1h 13 minutes

A decent AGM battery could sustain ~C*1 discharge (discharge to dead) -- But unless you are running power tools (or other loads that only operate for very sort times), a 1,000 Watt AC inverter on this small of battery is usually way over-sized for most people.

Facing the solar array from the sun/covering with dark material to "turn the panel off" is handy. If you connect the panel backwards directly the the battery--You can easily "fry" the panel (connecting panels backwards will be a dead short on a battery bank).

If you are connecting to the solar panel input on a solar charge controller--Connecting backwards should not damage panels, and many controllers are protected against reverse polarity (not all--Don't know about yours).

A 100 watt panel with 120 AH battery bank is about the minimum rate of charge we would recommend (120 AH * 5% minimum rate of charge = 6 amps minimum recommended rate of charge).

We really like to start with your loads--And design a system to support your needs... Of course we can start backwards--You have a battery (or solar panel) and what could the system power that would be useful to you.

More or less, a 10 amp @ 12 VDC or ~120 Watt load would be a more "reasonable" load for your system (i.e., emergency power).

-Bill
• Registered Users Posts: 8
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Re: Help with basic portable generator

the battery is actually a 120ah, not the 100ah stated in my previous reply
• Solar Expert Posts: 891 ✭✭✭✭
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Re: Help with basic portable generator
tyankee wrote: »
My question is can I keep charging the battery with the solar panel while running appliances through the inverter.
If more power is going in than going out - yes.

Example -
120 watts of panels. No MPPT controller so you will probably get 70-80 watts usable.
85% efficient inverter; now you are at about 60 watts

So if your load is 60 watts or less then you can run your loads in full sun. If they are less than that, you will also charge the battery.
• Registered Users Posts: 8
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Re: Help with basic portable generator
If more power is going in than going out - yes.

Example -
120 watts of panels. No MPPT controller so you will probably get 70-80 watts usable.
85% efficient inverter; now you are at about 60 watts

So if your load is 60 watts or less then you can run your loads in full sun. If they are less than that, you will also charge the battery.

ok, that makes some sense to me.. but the actual HOW is what i don't know.. do i connect the solar panels directly to the battery? there is a charge controller built into the solar panels but when i tried to do that with the Inverter on, the batter terminal gave a good spark.. or do i just have to turn off the inverter before i connect..
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Re: Help with basic portable generator

Say your 100 AH @ 12 volt battery ran for about 10 hours...

100 AH / 10 hour = ~10 amp average load

10 amps * 12 volts * 0.85 AC inverter eff = 102 Watts average load

Certainly possible... Laser printers may only draw ~10 Watts on standby--Can can draw 100's of watts when printing (heating up the fuser section to melt the toner into the paper).

In general, if you ran the battery dead--You have probably knocked several years off the life of the battery--and it may not even last more than a few weeks or months (lots of variables into "how dead" and what damage may have been caused to the battery).

In general, for longer life with typical lead acid deep cycle batteries--You are better off not drawing them much below 50% state of charge if you want longer battery life.

A great tool for learning about power usage is a Kill-a-Watt type meter... It tells you the basics about your AC power loads and helps you plan out your backup power system.

Kill-a-Watt type meters are also very helpful for looking at power use around your home and figuring out conservation plans.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 5,183 ✭✭✭✭
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Re: Help with basic portable generator

YES, you should always turn off any load device (ie Inverter) before connecting the PV (to the charge controller and then) to the battery... since your CC is built in the bracketed part is automatic.

KID #51B  4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
West Chilcotin, BC, Canada
• Solar Expert Posts: 252 ✭✭
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Re: Help with basic portable generator

I even turn the CC's breakers off before I do anything. Everything off or in your case covered too, then make your connections. Otherwise you may have a bad hair day.
• Registered Users Posts: 8
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Re: Help with basic portable generator

thanks a bunch ..
Alaska Man wrote: »
I even turn the CC's breakers off before I do anything. Everything off or in your case covered too, then make your connections. Otherwise you may have a bad hair day.
• Solar Expert Posts: 140 ✭✭
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Re: Help with basic portable generator
Example -
120 watts of panels. No MPPT controller so you will probably get 70-80 watts usable.

Assuming that the panels are rated for an output in the ballpark of 17.5-17.9 VDC, I'm skeptical that an MPPT charge controller would add any efficiency to their usable output. That being said, I conclude that back-of-the-envelope calculations (using the .77 derating that forum members commonly use) would indicate that these panels should realistically be expected to average around 92 Watts under peak sun conditions.

In short, I agree that the OP needs to understand that PV panel performance under Standard Test Conditions (STC) does not equal real-world PV panel performance; I'm just not sure that the non-MPPT derating you calculated applies in this case.
• Solar Expert Posts: 626 ✭✭✭
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Re: Help with basic portable generator

All I know is that my BMS generator set up I found out is less efficient due to the PWM.

That is a key factor. I have 120watts (2) 60 watt panels @ 6.6 amps max, 18.5V. The pwm controller which is a sunforce rated at 10 amps, only charges my 125Ah battery under load at about 5.2 amps. The battery I have recommends a 10amp minimum for the charge. So for my set up it requires 3 days of sun @ 50%DOD.

While originally the calculations looked nice for a full charge in under three days, physical reality, poorly engineered PWM, and temperature variances don't really allow the circumstances to happen.

My set up is a little more or less industrial grade.
• Registered Users Posts: 8
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Re: Help with basic portable generator

so to put this in my newbie terms, let me see if i have this right..

i should bet around 60 -80 watts of usable power before the battery needs to be recharged - with this current system? what's confusing me is i know i can run my computer, 1 printers, modem, phone, and small fan - all at the same time - for about 8 -16 hours before the power shuts off coming from the inverter via battery. that doesn't seem to jive with what everyone is telling me here.
• Registered Users Posts: 8
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Re: Help with basic portable generator

good stuff... is there a way to get notified when the battery gets to a point where it needs to be recharged?? i know there is a simple battery tester hooked up to this that if i push a button, it tells me when it needs to be recharged and i can turn off the inverter.. but i don't want to have to keep pushing the button to see.. and i certainly don't want to drain the battery completely..

BB. wrote: »
Say your 100 AH @ 12 volt battery ran for about 10 hours...

100 AH / 10 hour = ~10 amp average load

10 amps * 12 volts * 0.85 AC inverter eff = 102 Watts average load

Certainly possible... Laser printers may only draw ~10 Watts on standby--Can can draw 100's of watts when printing (heating up the fuser section to melt the toner into the paper).

In general, if you ran the battery dead--You have probably knocked several years off the life of the battery--and it may not even last more than a few weeks or months (lots of variables into "how dead" and what damage may have been caused to the battery).

In general, for longer life with typical lead acid deep cycle batteries--You are better off not drawing them much below 50% state of charge if you want longer battery life.

A great tool for learning about power usage is a Kill-a-Watt type meter... It tells you the basics about your AC power loads and helps you plan out your backup power system.

Kill-a-Watt type meters are also very helpful for looking at power use around your home and figuring out conservation plans.

-Bill
• Solar Expert Posts: 5,183 ✭✭✭✭
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Re: Help with basic portable generator

I'll try to make it simpler

you have a solar panel, derate it by .77 for realistic output over 4 hrs per day: 100W really means 77W x 4 hrs

you do NOT want to use more than 50% of your battery each day if you want it to give you reliable service:
120Ahr really means 60Ahr

you need to measure the loads of all the devices so that they do not exceed both (or either) the 50% or the daily PV production.

you need to replace 110% or more of what you use to fully recharge your battery daily

It is your choice

If you do you exceed those limits you are getting into a death spiral for your battery...it can be very slow but fatal

KID #51B  4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
West Chilcotin, BC, Canada
• Solar Expert Posts: 891 ✭✭✭✭
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Re: Help with basic portable generator
tyankee wrote: »
ok, that makes some sense to me.. but the actual HOW is what i don't know.. do i connect the solar panels directly to the battery? there is a charge controller built into the solar panels but when i tried to do that with the Inverter on, the batter terminal gave a good spark.. or do i just have to turn off the inverter before i connect..
You will get a spark when you first connect the inverter and usually when you connect the charge controller due to internal capacitance charging up. (Assuming you have polarities right etc.) That's pretty normal. Most people use switches or circuit breakers if they will be connecting/disconnecting often. In general keep inverters off when doing any maintenance or connection/disconnection of devices.
• Solar Expert Posts: 891 ✭✭✭✭
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Re: Help with basic portable generator
tyankee wrote: »
so to put this in my newbie terms, let me see if i have this right..

i should bet around 60 -80 watts of usable power before the battery needs to be recharged
You're making the energy vs power mistake here. You can get tremendous amounts of power from a battery for a short time. You can get 1000 watts of usable power for a few minutes from this setup, for example. That's power. But what you really care about is energy, which is watt-hours.
what's confusing me is i know i can run my computer, 1 printers, modem, phone, and small fan - all at the same time - for about 8 -16 hours before the power shuts off coming from the inverter via battery. that doesn't seem to jive with what everyone is telling me here.
Right, because you are running on stored power at that point. Your battery contains a certain number of available watt-hours. Solar puts energy into the battery. The inverter takes it out. As long as you put the same amount (or more) in then you are in good shape.
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Re: Help with basic portable generator
AuricTech wrote: »
Assuming that the panels are rated for an output in the ballpark of 17.5-17.9 VDC, I'm skeptical that an MPPT charge controller would add any efficiency to their usable output.
I've found it depends on use case. I have a cheap Blue Sky Energy MPPT charge controller for a 12 volt system that I loan out to people (a local ham club uses it for some sort of "preparedness day" they have.) I get another quarter to half an amp with that, compared to direct connection to the battery.

But in most cases it won't be much. I have a feeling that in warmer climates and with batteries that are usually in float, the difference would be almost unnoticeable.
• Solar Expert Posts: 3,123 ✭✭✭✭
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Re: Help with basic portable generator
... Solar puts energy into the battery. The inverter takes it out. As long as you put the same amount (or more) in then you are in good shape.
Except, of course, that the timing is important too, as is the depth to which you discharge the battery bank. Regular 80% discharge will reduce the life of lead-acid batteries tremendously.
SMA SB 3000, old BP panels.
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Re: Help with basic portable generator
tyankee wrote: »
good stuff... is there a way to get notified when the battery gets to a point where it needs to be recharged?? i know there is a simple battery tester hooked up to this that if i push a button, it tells me when it needs to be recharged and i can turn off the inverter.. but i don't want to have to keep pushing the button to see.. and i certainly don't want to drain the battery completely..
Golf cart battery DOD gauge for 12/24V batteries \$25 on amazon
• Registered Users Posts: 8
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Re: Help with basic portable generator

how do you 'measure the loads'???

westbranch wrote: »
I'll try to make it simpler

you have a solar panel, derate it by .77 for realistic output over 4 hrs per day: 100W really means 77W x 4 hrs

you do NOT want to use more than 50% of your battery each day if you want it to give you reliable service:
120Ahr really means 60Ahr

you need to measure the loads of all the devices so that they do not exceed both (or either) the 50% or the daily PV production.

you need to replace 110% or more of what you use to fully recharge your battery daily

It is your choice

If you do you exceed those limits are getting into a death spiral for your battery...it can be very slow but fatal
• Super Moderators, Administrators Posts: 33,541 admin
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Re: Help with basic portable generator

There are several ways--Depends on what you are measuring.

For simple plug in 120 VAC loads, a Kill-a-Watt type meter is great.

For DC loads (not too large), a DC Amp*Hour/Watt*Hour meter.

For random/large loads, you can use an AC/DC Current Clamp DMM.

All of the above are pretty cheap. The first too are nice because they "totalize" the amount of energy used (over hours to days).

The last one is a very handy test/diagnostic tool. Current Clamp meters are also easier and safer to measure current vs having to "cut a wire and insert a meter".

There are a lot of other options out there, but for smaller loads and off grid power systems, the above are a good and relatively cheap set of solutions for a starting point.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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Re: Help with basic portable generator
tyankee wrote: »
how do you 'measure the loads'???

Bill in reply #7 posted a link to a Kil-A-Watt meter which will give you a good idea about your AC loads, the inverter will also a be a load both in use, only @85% efficient and if not turned off after use a steady draw in idle.
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
- Assorted other systems, pieces and to many panels in the closet to not do more projects.