Matching generator with battery charger?

Registered Users Posts: 2
I'm looking to run maybe an ARB fridge, charge laptop, maybe run a TV, etc... from a battery bank. Probably 120 A bank, and probably going to use 30 or so amps a day.

I'm going to try and be in the shade as much as possible, so I am assuming solar is out (trying to get 60 amps a day in the shade).

So I am thinking of one of these http://www.amazon.com/Earthquake-11613-Portable-Generator-Compliant/dp/B00FL89I2W/ref=sr_1_1?ie=UTF8&qid=1410314858&sr=8-1&keywords=earthquake+generator

Which is rated at 700/800 watts. I assume I need to be around 50% load, so 350 watts input to charger would be ideal.

Now, Progressive Dynamics puts lists the input watts for their chargers, but I am not seeing this figure for other brands. I see a VAC input rating, but I don't know how that relates to the amount of watts being input.

So basically, how do I tell if this http://www.xantrex.com/documents/Battery-Chargers/TRUECharge-2/DS_TC2_20_40_60_20110303.pdf or this http://www.iotaengineering.com/dls30.htm ...

... is going to be too much for the 700/800 inverter generator?

I am only seeing input values for a VAC, which I cannot figure out how that applies to output watts from the generator.

Say I am charging a 120 A battery bank from 50% to 90%. I wonder how long the charger will be in the bulk stage, etc...

I have read that 13.8 (volts) times the amps gives the input watts, but that formula doesn't seem to match exactly to Progressive Dynamics figures.

Is there a formula using the amps, or the VAC, etc...?

Also, any advice on a specific, inexpensive (around \$100 - \$150) smart charger for this set up will be greatly appreciated. I am out of my realm here. I was advised on the Iota 30 amp, but am reading that it is non correcting, etc... I just want a good, inexpensive/best bang for buck way to charge batteries.

Thank you very much in advance for any help.

Re: Matching generator with battery charger?

Welcome to the forum Guy!

Guysakar wrote: »
I'm looking to run maybe an ARB fridge, charge laptop, maybe run a TV, etc... from a battery bank. Probably 120 A bank, and probably going to use 30 or so amps a day.

Note that Energy Used is:

Energy = Watts * Hours of run time = Volts * Amps * Hours

For AH to be useful, I need to know at what voltage. 30 AH * 12 volts = 360 Watt*Hours (per day?). That is not very much power.

Your battery is probably a 120 Amp*Hour * 12 volts = 1,440 Watt*Hours of storage -- And we typically recommend not going below 50% state of charge before recharging (lead acid battery cycle life gets worse the deeper you cycle it).

The ARB Fridge--If this is the right one and I understand their marketing documents may use ~1 amp @ 12 volts average or:

1 amp * 24 hours per day = 24 AH per day
1 amp * 24 hours per day * 12 volts = 288 Watt*Hours per day

A laptop computer may run 20-30 watts average and 60-100 Watts when recharging... If you run the laptop 6 hours per day:

30 watts * 6 hours = 180 Watt*Hours per day

So--Just a small refrigerator and laptop--We probably have met your 30 AH @ 12 volt (360 Watt*Hours) per day loads...
I'm going to try and be in the shade as much as possible, so I am assuming solar is out (trying to get 60 amps a day in the shade).

Yep--Shade is not going to cut it... However, a few folks have a couple of ~140 Watt solar panels that they setup in the sun (staked to ground) and the RV in the shade. Panels are tempered glass (careful not to break) and they can "walk" if you don't keep an eye on them.

The problem with Lead Acid batteries is that they are not really very "generator friendly". It would take 3-5+ hours of run time to recharge a Lead Acid battery bank (they charge pretty quickly up to 80% state of charge, above that, it takes another 2-4+ hours to recharge to 100% state of charge). There are some games you can play--But if you don't want to run the genset for many hours every day--You might want to rethink loads/battery type/portable solar/etc.

Your usage may be a really good canidate for LiFePO4 batteries. They are not cheap--But should have a good life and much better charging profile (you don't have to hold charging voltage for 2-4+ hours at the tail of the charging profile). Definitely something to look at.
Which is rated at 700/800 watts. I assume I need to be around 50% load, so 350 watts input to charger would be ideal.

Very reasonable assumption.
Now, Progressive Dynamics puts lists the input watts for their chargers, but I am not seeing this figure for other brands. I see a VAC input rating, but I don't know how that relates to the amount of watts being input.

More or less say 20 amp @ 12 volt charger:

Input power = 20 amps * 14.5 volts DC charging * 1/0.80 charger efficiency = 362.5 Watts (estimate) from 120 VAC genset

Both are good chargers, but very different in design... I suggest not getting too far ahead yet picking hardware.

... is going to be too much for the 700/800 inverter generator?

I am only seeing input values for a VAC, which I cannot figure out how that applies to output watts from the generator.

Say I am charging a 120 A battery bank from 50% to 90%. I wonder how long the charger will be in the bulk stage, etc...

I have read that 13.8 (volts) times the amps gives the input watts, but that formula doesn't seem to match exactly to Progressive Dynamics figures.

Is there a formula using the amps, or the VAC, etc...?

One (very rough) estimate above... If 20 amp charger on 12 volt 120 AH battery:

50-80% SOC = 30% points
120 AH * 0.3 capacity / 20 amp charging = 1.8 hours bulk charging
80%-90%+ state of charge = ~3-4 hours of absorb charging
Also, any advice on a specific, inexpensive (around \$100 - \$150) smart charger for this set up will be greatly appreciated. I am out of my realm here. I was advised on the Iota 30 amp, but am reading that it is non correcting, etc... I just want a good, inexpensive/best bang for buck way to charge batteries.

The Iota would be fine (it is adjustible)--And you will be monitoring DC charging current--That will tell you when you want to shut down the genset (you don't want the generator running "unloaded/unneeded"--Waste of fuel).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 2
Re: Matching generator with battery charger?
BB. wrote: »
Welcome to the forum Guy!

Note that Energy Used is:

Energy = Watts * Hours of run time = Volts * Amps * Hours

For AH to be useful, I need to know at what voltage. 30 AH * 12 volts = 360 Watt*Hours (per day?). That is not very much power.

Your battery is probably a 120 Amp*Hour * 12 volts = 1,440 Watt*Hours of storage -- And we typically recommend not going below 50% state of charge before recharging (lead acid battery cycle life gets worse the deeper you cycle it).

The ARB Fridge--If this is the right one and I understand their marketing documents may use ~1 amp @ 12 volts average or:

1 amp * 24 hours per day = 24 AH per day
1 amp * 24 hours per day * 12 volts = 288 Watt*Hours per day

A laptop computer may run 20-30 watts average and 60-100 Watts when recharging... If you run the laptop 6 hours per day:

30 watts * 6 hours = 180 Watt*Hours per day

So--Just a small refrigerator and laptop--We probably have met your 30 AH @ 12 volt (360 Watt*Hours) per day loads...

Yep--Shade is not going to cut it... However, a few folks have a couple of ~140 Watt solar panels that they setup in the sun (staked to ground) and the RV in the shade. Panels are tempered glass (careful not to break) and they can "walk" if you don't keep an eye on them.

The problem with Lead Acid batteries is that they are not really very "generator friendly". It would take 3-5+ hours of run time to recharge a Lead Acid battery bank (they charge pretty quickly up to 80% state of charge, above that, it takes another 2-4+ hours to recharge to 100% state of charge). There are some games you can play--But if you don't want to run the genset for many hours every day--You might want to rethink loads/battery type/portable solar/etc.

Your usage may be a really good canidate for LiFePO4 batteries. They are not cheap--But should have a good life and much better charging profile (you don't have to hold charging voltage for 2-4+ hours at the tail of the charging profile). Definitely something to look at.

Very reasonable assumption.

More or less say 20 amp @ 12 volt charger:

Input power = 20 amps * 14.5 volts DC charging * 1/0.80 charger efficiency = 362.5 Watts (estimate) from 120 VAC genset

Both are good chargers, but very different in design... I suggest not getting too far ahead yet picking hardware.

One (very rough) estimate above... If 20 amp charger on 12 volt 120 AH battery:

50-80% SOC = 30% points
120 AH * 0.3 capacity / 20 amp charging = 1.8 hours bulk charging
80%-90%+ state of charge = ~3-4 hours of absorb charging

The Iota would be fine (it is adjustible)--And you will be monitoring DC charging current--That will tell you when you want to shut down the genset (you don't want the generator running "unloaded/unneeded"--Waste of fuel).

-Bill

I read everything twice, and I think I got most of it.

I have read that 13.8 (volts) times the amps gives the input watts, but that formula doesn't seem to match exactly to Progressive Dynamics figures.

Input power = 20 amps * 14.5 volts DC charging * 1/0.80 charger efficiency = 362.5 Watts (estimate) from 120 VAC genset

I see now that the inefficiency is what was being left out of the equation. Plugging the 20% inefficiency rate into the volts times amps = watts equation, adds up to the known figures for the Progressive Dynamics chargers. Thus, I think I can now figure out the input watts from other brands. Thank you!

Both are good chargers, but very different in design... I suggest not getting too far ahead yet picking hardware.

I'm not seeing a lot of options for a 20-25 amp smart charger, and I am getting a bit lost in all of the differences. I was all set on the Progressive, but 45 amps is their smallest. Is there just a simple smart charger that is a good bank for buck, or maybe a standard?

The best option I have found thus far is the CTEK 25/2500. The guy on this page claims this charger will put 80 amps back in a 200 amp battery bank (from 50% to 90%) in 4 hours, which I am more than happy with. But, it is a little pricey at \$200, and there just isn't as much resources and word of mouth on them like with the Progressive or other brands.

Again, thank you very much for your help. Exactly what I was looking for.
• Solar Expert Posts: 3,123 ✭✭✭✭
Re: Matching generator with battery charger?
Guysakar wrote: »
... claims this charger will put 80 amps back in a 200 amp battery bank (from 50% to 90%) in 4 hours, which I am more than happy with. But, it is a little pricey at \$200, and there just isn't as much resources and word of mouth on them like with the Progressive or other brands.
That would be 80AH, not 80A.
And 200AH, not 200A.
SMA SB 3000, old BP panels.
• Solar Expert Posts: 2,490 ✭✭✭
Re: Matching generator with battery charger?

If your really serious about the money that you spend I'd recommend you look at a Honda EU 1000 or even a EU 2000 generator as a much better investment. The EU 2000 will pull a 30 amp IOTA in ECO idle and you have to go look at it to make sure it's still running and will run 8 hours or so on a gallon of gas.

Don't get to far down in the weeds with all the EE specifications trying to save a thimble of fuel over a 8 hr run, unless your trying to spend 2x the amount.

NAWS has The IOTA in standard DLS-30 for \$135 + \$15 for the DLS plug in module. It's best to buy it that way so you can use it as a fixed voltage output charger or as a controlled 3 stage.

http://www.solar-electric.com/batteries-meters-accessories/bach2/bach1/dls-30.html
Re: Matching generator with battery charger?

Before you get into the "smart charger"--Which if you are 100% generator/solar powered is not really needed--If you will have grid power (parked at home, sometimes at RV park, etc.), then a smart AC charger might be nice.

Figure out your loads first... That sizes your battery bank. Then you have enough information to figure out the rest of the system.

A refrigerator is typically what moves a "small system" to a "medium/larger" system design. Many times, a propane refrigerator is not a bad choice for an RV/weekend/seasonal use. A full electric refrigerator can make economic sense for off grid use, but usually for 9+ month of the year type use.

Computers can be a pretty big power hog too... The average power (Watts) may not be that much--But if it is used 12+ hours per day (Watt*Hours), then the overall energy use per day can be very significant.

That is why knowing your loads and conservation is so important for off grid systems. Batteries are "terrible" at storing energy (a car battery stores about the same amount of useful energy as 1 cup of gasoline). Reducing electrical loads to the minimum really helps make for a more cost effective power system.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 203 ✭✭✭✭✭
Re: Matching generator with battery charger?

When sizing my charger to my battery bank (45 amp charger for 225 ah battery bank) I used a 20% charge rate, which is on the high side. 10% is often used, but there's a trade off between gasoline usage, generator life, and battery life. Given the costs of my batteries vs. my generator, I'd rather have to replace the batteries.

You might have a hard time getting your battery fully charged on a generator unless you run it for a long time. Bulk is easy, it's the absorption phase that will take the longest.

I have an Iota DLS-45 with a detachable IQ4 module (this controls the "smart charging" function). I had to adjust the potentiometer to get the 14.8V that my Trojan batteries want, which makes the IQ4 useless. My plan is to use the Iota in the winter during rainy periods when my panels aren't producing much, just to bulk the batteries and keep the state of charge as high as possible until my panels can take over and finish the charge.

I agree with Blackcherry that you should consider a Honda EU1000 or 2000 rather than an off brand generator. Costs a bit more, but they're very well regarded, and the resale value will be greater if you need to sell it down the road. I have an old Honda EB3500, which is excessive for my 45-amp charger, not to mention really loud and a bit of a gas hog. One of these days I may sell it and buy a Honda EU2000.
Re: Matching generator with battery charger?

Having two generators (or more) is not out of the ordinary either...

A big "noise maker" to bulk the battery bank, run the ship tools, etc. (and as a backup genset). And as the loads decrease (absorb in battery bank, a few things at night when the AC inverter failed, etc.), a smaller/quiet genset that will burn less fuel than the big genset with smaller loads will...

Basically, as the generator becomes less than 1/2 loaded--The fuel flow (for a gasoline genset) will remain pretty close to 50% fuel flow. So, once you get down below a 1,000 watts or so of AC load, the little Honda and Yamaha (et. al.) gensets will let you get the AC power without huge fuel bills from the big genset...

A 7 kWatt genset may burn close to 1 gallon of fuel per hour at 50% or less load... A small 1,600 Watt Honda or Yamaha will burn around 1/4 to 1/10 gallon per hour (1,600 watts to zero Watts).

The right tool for the right job.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset