My mechanic is telling me that engines regulate the amperage the alternator puts out. I dont know much but from what i understand the higher amperage alternator the faster your batteries will charge, but my mechanic says the engine brings any alternator down to 100 amps regardless, does this make any sense to anyone. And does anyone here know of any good sites for auxiliary design, im learning but don't have the time to become an expert. And in case anyone here is, we are looking at about 200amp hours max usage, we have (2) 75watt panels now and plan to have around (3) 100 AH batteries. Just need to know how long this would allow us to dry camp and how hard will it be to keep the batteries full enough so that we are not going to kill them. Either way thanks for any help in advance :gunt:
Alternators
- Thread starter Tress
- Start date
Time to get a new mechanic!
Alternators vary in output. Old Land Cruiser for instance make 35 amps, and some modern full-size rigs make 200 amps or more. There is no magic upper limit at 100 amps. That's just laughable. Most alternators make their full output at 1500 rpm, so if you know the output, you can roughly calculate how long it will take to charge a bank of batteries, assuming your running rpm is above idle and there arn't major losses in your system.
Let's say you have three 100 amp hour batteries and they are fully drained. Let's also assume your alternator makes 100 amps. You could realistically expect to charge your batteries in roughly 3 hours of running. If the alternator makes 200 amps, your charge time would be 90 minutes. In reality, it normally doesn't take that long, because batteries are rarely discharged flat. Your 75 watt panels will decrease your need to run the motor a little, but that's not much power.
Alternators vary in output. Old Land Cruiser for instance make 35 amps, and some modern full-size rigs make 200 amps or more. There is no magic upper limit at 100 amps. That's just laughable. Most alternators make their full output at 1500 rpm, so if you know the output, you can roughly calculate how long it will take to charge a bank of batteries, assuming your running rpm is above idle and there arn't major losses in your system.
Let's say you have three 100 amp hour batteries and they are fully drained. Let's also assume your alternator makes 100 amps. You could realistically expect to charge your batteries in roughly 3 hours of running. If the alternator makes 200 amps, your charge time would be 90 minutes. In reality, it normally doesn't take that long, because batteries are rarely discharged flat. Your 75 watt panels will decrease your need to run the motor a little, but that's not much power.
You can say that agin, he's a nice guy and has helped us out a good deal but we have had our problems with him. Either way, thanks for the info. So the 150 watts aint much huh, we have a really small fridge but its 12v no propane, plus a microwave, water pump, lights and a computer but no tv or air con. We are kind of hoping the panels might be able to supply the fridge, at least for the most part. But it sounds like we're going to need a big bank and prolly a bigger alternator, still working on another panel.
The microwave will be a major power sucker as are most lights. The computer as well will suck power.
A lot will depend on how much you're stationary and how much you drive. If you drive everyday, none of this will be an issue. If you want to camp days at a time, leave everything off but the fridge.
I have a single 50 amp hour battery in my FJ40 and it can sit for about 3 days running the fridge and nothing else before the battery is dead flat. Keep the fridge cool and shaded and that helps too.
Are you really taking a microwave? Maybe just leave that home and your power issues are 95% solved.
A lot will depend on how much you're stationary and how much you drive. If you drive everyday, none of this will be an issue. If you want to camp days at a time, leave everything off but the fridge.
I have a single 50 amp hour battery in my FJ40 and it can sit for about 3 days running the fridge and nothing else before the battery is dead flat. Keep the fridge cool and shaded and that helps too.
Are you really taking a microwave? Maybe just leave that home and your power issues are 95% solved.
egn
Adventurer
AndrewP said:
There are several reasons why you are wrong here:
1. Most battery types don't accept such a high current
There are a lot of different lead acid battery types. Only a few can accept such high currents during charging for a long time. The result is that the voltage goes up very fast to the regulator voltage and then the charge current drops automatically. So even your alternator has 200 A rating it may charge them only with 50 A.
2. Regulator voltage is typical to low to sustain high currents
Typical regulator voltage is about 14 V. As a rule of thumb, with this voltage you can expect with a typical battery a current of about 20 % of Ah rating till about 70 % state of charge. If you charge only with 10 % of Ah rating it goes up until about 80 % SOC until the current drops. If you go much higher with charging the 14 V will be reached much earlier. Then the charge current is constantly dropping. If the battery is really empty then it takes much more hours for the battery to become full than you would expect.
3. Voltage drop at high currents will reduce charge current further.
With very high current you get a very high voltage drop at the wiring and the battery poles. This reduces charge voltage even further below 14 V.
4. Typical regulators a temperature compensated and reduce charge voltage
If the the alternator gets hot because of the high current over a long time then the regulator will reduce charge voltage. This will reduce the the current the battery accepts.
5. There are other power consumers that reduce the available current for charging
When using your car there are a lot of other power consumers that are stealing from available charge current. All your standard appliances like radio, navigation system, lights, air cond., ... and the camper appliances like fridge use all together a lot of power. This can be more than 50 A alone.
So please do not be disappointed when you have changed only to a higher rated alternator and the charging takes to long.
The first thing you should do is to install an intelligent battery computer which shows not only the voltage and the current in and out of the battery, but also the state of charge of the battery. Only if you have information about the current flow and your power usage you can analyse what to do.
Before you upgrade the alternator you should look whether it already delivers the maximum current with a discharged battery. If it uses the maximum current then an upgrade is worthwhile.
The cheapest way to improve charging is normally in improve the wiring. The loss in the cable can be considerably and additionally the reduced voltage at the battery decreases the current acceptance of the battery.
The next thing to look ist the regulator. There are intellegent regulators or voltage boosters available that do a 3/4-stage charging with higher voltage. But look for one that has an external temperatur sensor at least for the battery. This avoids overcharging the battery which is especially critical if you use a non-flooded GEL or AGM battery. For flooded batteries this is not that critical, but you have to look at the liquid level regularily to avoid drying it out.
The best regulators have two additional sensors:
- An additional temperature sensor for the alternator to prevent overheating.
- An voltage sensor for the battery to allow compensation of voltage drop of the wiring.
With such a regulator you get the max out of your alternator and battery combination.
The only thing that may the charging even further is to use batteries with a very high current acceptance like the http://www.lifelinebatteries.com/ batteries. They can accept a multiple of its Ah rating as current till they are nearly full. But of course, they are very expensive. But be very careful. Without a temperatur sensor at the alternator the alternator may be killed if you have a high capacity installed. If they are nearly empty charging the battery is just like a shortcut.
I hope this answers most of the questions. As our motorhome is very dependend on electical energy with high power, I have optimized everything so far that with 1-2 hours drive about one day of energy usage can be charged. The AGM batteries are good for about one week typical usage. As we normally stay only about a maximum of 3-4 days until we move to a new place, we have absolute no energy problem.
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Grim Reaper
Expedition Leader
I think part of the confusion is just his explanation being poor.
Alternators have a RPM range they operate in. You have to "gear" the alternator to the RPM range the engine it is attached to operates in. The end result is running down the road turning say 2000 RPM on the engine is running the alternator at a speed where it can reach its full output.
Now where I think the confusion came in is very few vehicles are spinning the alternator fast enough at idle to be able to produce its "rated" output. So at a 800RPM idle a 100 amp alternator may only be capable of making about 50amps. At 2000 RPM it could achieve its full output.
This is why at night idling you may notice your lights brighten as you hit the gas.
Alternators have a RPM range they operate in. You have to "gear" the alternator to the RPM range the engine it is attached to operates in. The end result is running down the road turning say 2000 RPM on the engine is running the alternator at a speed where it can reach its full output.
Now where I think the confusion came in is very few vehicles are spinning the alternator fast enough at idle to be able to produce its "rated" output. So at a 800RPM idle a 100 amp alternator may only be capable of making about 50amps. At 2000 RPM it could achieve its full output.
This is why at night idling you may notice your lights brighten as you hit the gas.
outsidr
Adventurer
FYI the best resource I have for electrical set up is the techs at www.premierpowerwelder.com . Not only do they make a great alternator welder/charger they are also electrical engineers and have great insight to your system as a whole.
I run their equipment in both my trucks and one thing you can do to help your charge rate is to install a throttle position control system. If you have an older vehicle this can be as simple as a bicycle gear shifter that pulls the throttle body open as you push the shifter forward thus increasing RPM while at idle.
Another helpful equation I did not see above was Watts=Amps*Volts. You can use PEMDAS to move it around and figure your total output vs. draw to figure how long you can dry camp before cranking or needing additional support.
To be absolutely safe you can isolate your main battery with a IBS, Painless dual battery setup, powergate, or simple marine selector switch/cut off that will give you insurance in case you forgot to idles your rig.
As usual there are 1,000 solutions. Pick the one that best suits your long term build plans and needs.
I run their equipment in both my trucks and one thing you can do to help your charge rate is to install a throttle position control system. If you have an older vehicle this can be as simple as a bicycle gear shifter that pulls the throttle body open as you push the shifter forward thus increasing RPM while at idle.
Another helpful equation I did not see above was Watts=Amps*Volts. You can use PEMDAS to move it around and figure your total output vs. draw to figure how long you can dry camp before cranking or needing additional support.
To be absolutely safe you can isolate your main battery with a IBS, Painless dual battery setup, powergate, or simple marine selector switch/cut off that will give you insurance in case you forgot to idles your rig.
As usual there are 1,000 solutions. Pick the one that best suits your long term build plans and needs.
Ok so there is a ton of really good info here, i have read this post prolly 10 times now trying to fully understand, please see my comments/questions written in red below each item. And thanks so much for the detailed analysis!
:smilies27
1. Most battery types don't accept such a high current
There are a lot of different lead acid battery types. Only a few can accept such high currents during charging for a long time. The result is that the voltage goes up very fast to the regulator voltage and then the charge current drops automatically. So even your alternator has 200 A rating it may charge them only with 50 A.
So even a hi amp alternator might only put out 50amps, is this every hour?
2. Regulator voltage is typical to low to sustain high currents
Typical regulator voltage is about 14 V. As a rule of thumb, with this voltage you can expect with a typical battery a current of about 20 % of Ah rating till about 70 % state of charge. If you charge only with 10 % of Ah rating it goes up until about 80 % SOC until the current drops. If you go much higher with charging the 14 V will be reached much earlier. Then the charge current is constantly dropping. If the battery is really empty then it takes much more hours for the battery to become full than you would expect.
3. Voltage drop at high currents will reduce charge current further.
With very high current you get a very high voltage drop at the wiring and the battery poles. This reduces charge voltage even further below 14 V.
4. Typical regulators a temperature compensated and reduce charge voltage
If the the alternator gets hot because of the high current over a long time then the regulator will reduce charge voltage. This will reduce the the current the battery accepts.
5. There are other power consumers that reduce the available current for charging
When using your car there are a lot of other power consumers that are stealing from available charge current. All your standard appliances like radio, navigation system, lights, air cond., ... and the camper appliances like fridge use all together a lot of power. This can be more than 50 A alone.
So please do not be disappointed when you have changed only to a higher rated alternator and the charging takes to long.
The first thing you should do is to install an intelligent battery computer which shows not only the voltage and the current in and out of the battery, but also the state of charge of the battery. Only if you have information about the current flow and your power usage you can analyse what to do.
Do you have any suggestions for battery computers? Whats is a good one where is a good place to purchase?
Before you upgrade the alternator you should look whether it already delivers the maximum current with a discharged battery. If it uses the maximum current then an upgrade is worthwhile.
Will the battery computer tell me what the alternator is putting out? And how do i know what my alternator is supposed to put out, does it say ON the alternator?
The cheapest way to improve charging is normally in improve the wiring. The loss in the cable can be considerably and additionally the reduced voltage at the battery decreases the current acceptance of the battery.
So would you suggest using wire much bigger than needed? Or just slightly bigger? or just the right size?
The next thing to look is the regulator. There are intellegent regulators or voltage boosters available that do a 3/4-stage charging with higher voltage. But look for one that has an external temperatur sensor at least for the battery. This avoids overcharging the battery which is especially critical if you use a non-flooded GEL or AGM battery. For flooded batteries this is not that critical, but you have to look at the liquid level regularily to avoid drying it out.
I have searched for this thing all over the place, could you tell me where a good place to get one is? And you have any suggested brands to look for?
The best regulators have two additional sensors:
With such a regulator you get the max out of your alternator and battery combination.
The only thing that may the charging even further is to use batteries with a very high current acceptance like the http://www.lifelinebatteries.com/ batteries. They can accept a multiple of its Ah rating as current till they are nearly full. But of course, they are very expensive. But be very careful. Without a temperatur sensor at the alternator the alternator may be killed if you have a high capacity installed. If they are nearly empty charging the battery is just like a shortcut.
Im looking at 3 of the group 31's, Lifeline that is
I hope this answers most of the questions. As our motorhome is very dependend on electical energy with high power, I have optimized everything so far that with 1-2 hours drive about one day of energy usage can be charged. The AGM batteries are good for about one week typical usage. As we normally stay only about a maximum of 3-4 days until we move to a new place, we have absolute no energy problem.[/QUOTE]
Again thank you very much for your help, this is pretty complicated stuff for me and your explanaiton helped a lot.
:REExeSwimmingHL:
:smilies27
1. Most battery types don't accept such a high current
There are a lot of different lead acid battery types. Only a few can accept such high currents during charging for a long time. The result is that the voltage goes up very fast to the regulator voltage and then the charge current drops automatically. So even your alternator has 200 A rating it may charge them only with 50 A.
So even a hi amp alternator might only put out 50amps, is this every hour?
2. Regulator voltage is typical to low to sustain high currents
Typical regulator voltage is about 14 V. As a rule of thumb, with this voltage you can expect with a typical battery a current of about 20 % of Ah rating till about 70 % state of charge. If you charge only with 10 % of Ah rating it goes up until about 80 % SOC until the current drops. If you go much higher with charging the 14 V will be reached much earlier. Then the charge current is constantly dropping. If the battery is really empty then it takes much more hours for the battery to become full than you would expect.
3. Voltage drop at high currents will reduce charge current further.
With very high current you get a very high voltage drop at the wiring and the battery poles. This reduces charge voltage even further below 14 V.
4. Typical regulators a temperature compensated and reduce charge voltage
If the the alternator gets hot because of the high current over a long time then the regulator will reduce charge voltage. This will reduce the the current the battery accepts.
5. There are other power consumers that reduce the available current for charging
When using your car there are a lot of other power consumers that are stealing from available charge current. All your standard appliances like radio, navigation system, lights, air cond., ... and the camper appliances like fridge use all together a lot of power. This can be more than 50 A alone.
So please do not be disappointed when you have changed only to a higher rated alternator and the charging takes to long.
The first thing you should do is to install an intelligent battery computer which shows not only the voltage and the current in and out of the battery, but also the state of charge of the battery. Only if you have information about the current flow and your power usage you can analyse what to do.
Do you have any suggestions for battery computers? Whats is a good one where is a good place to purchase?
Before you upgrade the alternator you should look whether it already delivers the maximum current with a discharged battery. If it uses the maximum current then an upgrade is worthwhile.
Will the battery computer tell me what the alternator is putting out? And how do i know what my alternator is supposed to put out, does it say ON the alternator?
The cheapest way to improve charging is normally in improve the wiring. The loss in the cable can be considerably and additionally the reduced voltage at the battery decreases the current acceptance of the battery.
So would you suggest using wire much bigger than needed? Or just slightly bigger? or just the right size?
The next thing to look is the regulator. There are intellegent regulators or voltage boosters available that do a 3/4-stage charging with higher voltage. But look for one that has an external temperatur sensor at least for the battery. This avoids overcharging the battery which is especially critical if you use a non-flooded GEL or AGM battery. For flooded batteries this is not that critical, but you have to look at the liquid level regularily to avoid drying it out.
I have searched for this thing all over the place, could you tell me where a good place to get one is? And you have any suggested brands to look for?
The best regulators have two additional sensors:
- An additional temperature sensor for the alternator to prevent overheating.
- An voltage sensor for the battery to allow compensation of voltage drop of the wiring.
With such a regulator you get the max out of your alternator and battery combination.
The only thing that may the charging even further is to use batteries with a very high current acceptance like the http://www.lifelinebatteries.com/ batteries. They can accept a multiple of its Ah rating as current till they are nearly full. But of course, they are very expensive. But be very careful. Without a temperatur sensor at the alternator the alternator may be killed if you have a high capacity installed. If they are nearly empty charging the battery is just like a shortcut.
Im looking at 3 of the group 31's, Lifeline that is
I hope this answers most of the questions. As our motorhome is very dependend on electical energy with high power, I have optimized everything so far that with 1-2 hours drive about one day of energy usage can be charged. The AGM batteries are good for about one week typical usage. As we normally stay only about a maximum of 3-4 days until we move to a new place, we have absolute no energy problem.[/QUOTE]
Again thank you very much for your help, this is pretty complicated stuff for me and your explanaiton helped a lot.
:REExeSwimmingHL:
Robthebrit
Explorer
Tress said:
No.. The current from an alternator or any other device is assumed to be instantaneous and sustainable. Therefore a 100A alternator is equivalent to 100 amp/hours in battery terms.
Lets go back to basics, you can't force current through something. Remember V=I*R, therefore the only way a device can consume more current is to either raise the voltage or lower the resistance (in the case of a battery the Peukert number).
In the example given, your batteries may only be capable of consuming 50A at the charge voltage so the fact your alternator can make 200A is irrelevent unless you happen to have 4 such batteries then the alternator would happily charge them all in the same amount of time as it takes to charge one.
The amount of current a batter can sink depends on the type of battery, charge voltage, the depth of discharge, the temperature etc etc Once you can provide the maximum an alternator upgrade is not much use as far as the batteries are concerned. If you have other high current devices that operate while the engine is running (amplifier for example) then once again a higher capacity alternator makes sense.
You don't want the alternator to run at max capacity for hours and hours, so if you compute your total amperage to be 100A then get something around 150A. As a rule of thumb you want the amp hour capacity of the battery bank to be less than 4x the peak capacity of the alternator. For example a 150A alternator is enough to charge 600 amp/hour battery bank without any significant problems.
The best advise given above was to measure the currents and voltages. Getting a slightly higher charge voltage at the battery by using larger wiring can make a fair difference.
Rob
egn
Adventurer
Tress said:
As Rob wrote, the alternator will put out this amps constantly as long as there is a sink that accepts them.
It depends how much money you want to spend. There is a large price range. Here in Europe you can spend $150 but also $600 for such a device. They have different functionality and some can track the state-of-charge better than others. Search for "battery monitor" or "battery meter". You will find some.
I personally use the BTM-III from Mastervolt. The advantage vor me is that I can see the state-of-charge easily and don't have to press any keys to get the full info like voltage, amp in/out, SOC, hours till empty. It also tracks the SOC very well because it resets itself when the battery is fully charged and also uses charging efficiency and Peukert to improve tracking. The last is especially importent if you have very high discharge currents.
The battery monitor will provide information about the current that is going in/out battery. It is better to use a regular clamp amp meter first. With this you can check every wire separately. So you can find out what amps the alternator is putting out in total and what is going into the battery and to other devices. That is a really useful device.
It really depends how long the cables are and how much voltage drop they produce at given amps. I use about AWG 2/0 (70 sqmm metric) for my 150 A alternator.
During charging measure the voltage at the alternator and at a the discharged battery. The voltage at the battery shouldn't be more than 13 V during this test to have a substantial current flowing into the battery. If then the voltage at the alternator is higher more than 0,3 V than you should increase the wiring.
Look into marine shops. One of the well known companies in the states is http://www.amplepower.com/ . In Europe http://www.sterling-power.com and http://www.mastervolt.com is well known.
Sterling Power has nice devices that allow to get intelligent charging without modifying the alternator:
http://www.sterling-power.com/products-altbatt.htm
http://www.sterling-power.com/products-battbatt.htm
I have used both and they work well.
That is a good choice. Please read the info on the following website:
http://www.vonwentzel.net/Battery/index.html
You're welcome. :wavey:
Yes, this is very complicated stuff. But you can find a lot of info in the internet, especially at sites with marine info.
Ok, so i am going to try this a different way here; I really appreciate all the info provided and i really am feeling more comfortable with what we're talking about here but im still not confident in deciding on a solution. I even emailed Ample Power requesting some design assistance and essentially they told me to read a book. :violent-smiley-031:
We already have a Voltmeter and plan to take some readings this weekend to see what our alternator is capable of, I'm not even sure what its supposed to put out. While we are at it what would everyone suggest we measure aside from the alternator output?
Anyways it sounds to me like a monitor will be essential, as will a 3/4 stage alternator charger. Would this http://www.amplepower.com/products/sarv3/index.html suffice? and would it take the place of my existing regulator? THis unit does not appear to monitor the temp of the alternator????
Either way here is the list of what we expect our power needs to be, please look over the numbers and tell me if there is something im missing or more importantly what you would suggest we do. Basically im worried that if we just install a big *** battery bank then we very well might fry our alternator, im also worried that if i just get a smart regulator than it might not help much. No matter what we plan to get the (3) Group 31 Lifelines, quality hi gauge wire and some type of smart regulator.
Appliance----- Amps------- Avg. Hrs Used Daily--------- Amp Hours Used in a Day
12V Norcold Fridge------ 2.7----- 24----- 65
Laptops----- 4.6----- 2.5----- 11.5
Microwave 800Watt----- 10----- 0.1----- 1
Water Pump----- 8----- 0.15------ 1.2
Ceiling Fan/Vent----- 2.5----- 3------ 7.5
Oscillating Fan----- 3------ 6-------- 18
Coffee Maker------ 46----- 0.08------ 3.68
Lights------ 2.4------ 4------ 9.6
Stereo------ 3.3----- 4----- 13.2
Estimated Amp Hours Needed 130.68
So ya, theres what we're thinking, i cant tell you guys how much i appreciate your help, i hadnt anticipated this part of the project being so complex, ore expensive! So thank you again for the help, talk to you soon.
eepwall:
We already have a Voltmeter and plan to take some readings this weekend to see what our alternator is capable of, I'm not even sure what its supposed to put out. While we are at it what would everyone suggest we measure aside from the alternator output?
Anyways it sounds to me like a monitor will be essential, as will a 3/4 stage alternator charger. Would this http://www.amplepower.com/products/sarv3/index.html suffice? and would it take the place of my existing regulator? THis unit does not appear to monitor the temp of the alternator????
Either way here is the list of what we expect our power needs to be, please look over the numbers and tell me if there is something im missing or more importantly what you would suggest we do. Basically im worried that if we just install a big *** battery bank then we very well might fry our alternator, im also worried that if i just get a smart regulator than it might not help much. No matter what we plan to get the (3) Group 31 Lifelines, quality hi gauge wire and some type of smart regulator.
Appliance----- Amps------- Avg. Hrs Used Daily--------- Amp Hours Used in a Day
12V Norcold Fridge------ 2.7----- 24----- 65
Laptops----- 4.6----- 2.5----- 11.5
Microwave 800Watt----- 10----- 0.1----- 1
Water Pump----- 8----- 0.15------ 1.2
Ceiling Fan/Vent----- 2.5----- 3------ 7.5
Oscillating Fan----- 3------ 6-------- 18
Coffee Maker------ 46----- 0.08------ 3.68
Lights------ 2.4------ 4------ 9.6
Stereo------ 3.3----- 4----- 13.2
Estimated Amp Hours Needed 130.68
So ya, theres what we're thinking, i cant tell you guys how much i appreciate your help, i hadnt anticipated this part of the project being so complex, ore expensive! So thank you again for the help, talk to you soon.
eepwall:
Last edited:
Martyn
Supporting Sponsor, Overland Certified OC0018
Spend a little time calculating your power requirements. How many amps is each appliance and how long will you be using it for in a 24 hour period. If you are running modified sine wave inverter remember that the inverter draws power and does not run at 100% efficiency, a 50 watt bulb may require 65 watts of power on an inverter to power it.
Calculate the longest period of time you will be in base camp without starting the engine. The alternator will charge the batteries. Multiply the amount of daily power required by the number of static days in camp and you have your total power requirements.
Try to stay away from using 120 volt appliances. Check out places like Camping World to try to find 12 volt equivalents.
I don't know if this has been mentioned but the period of time it takes to charge the aux. batteries will also be dependant of the gauge of wire running from the alternator. 6 gauge will decrease the charge time where as 10 gauge will increase the charge time.
The lower part of http://www.adventuretrailers.com/12volt_solar.html has some of the theory.
Calculate the longest period of time you will be in base camp without starting the engine. The alternator will charge the batteries. Multiply the amount of daily power required by the number of static days in camp and you have your total power requirements.
Try to stay away from using 120 volt appliances. Check out places like Camping World to try to find 12 volt equivalents.
I don't know if this has been mentioned but the period of time it takes to charge the aux. batteries will also be dependant of the gauge of wire running from the alternator. 6 gauge will decrease the charge time where as 10 gauge will increase the charge time.
The lower part of http://www.adventuretrailers.com/12volt_solar.html has some of the theory.
Robthebrit
Explorer
There is a typo in your calculations above, an 800W Microwave will take more than 10A, more like 100A when you consider actual power consumed and inverter losses. Sure you are only running it for 0.1 hours so 10A/hour total, but 100A is a heavy and Peukert will start to play an issue.
Rob
Rob