Laptop charging

[Felipe Blanco]

 

Hi everyone. I have recently purchased a 1991 Hobby 600 and I'm very excited about it, although I'm a complete dummy about every aspect of RVs. I am trying to find the best solution to charge my laptop. The RV came with an old inverter and I have a brand new 55A lead acid battery which I intend to connect to the inverter. The idea is to use it exclusively to charge my notebook while traveling. It won't be connect to the alternator so it won't charge on its own. I have a battery charger though. My plan is to use the lead acid battery to charge the computer's battery for a couple of hours everyday, for a week, and at the end of the week charge the lead acid battery with the external charger. Would that work?

I'm attaching photos of the power adaptor and its info. I'm also uploading a photo of my inverter.

Thank you.

Felipe

[Chad Heiser]

That inverter looks to be a European style inverter putting out 220 volts at 50 hertz.  Do not plug any US style electrical appliances into that inverter as you will fry them.  US power standard is 120 volts at 60 hertz.

As to your question about using an inverter to charge your laptop for a week and then recharging the battery at the end of the week, the answer is it depends.  If your battery is truly only 55 amp hour rated, that means it only has approximately 27.5 amp hours of available power (because you do not want to draw the battery below 50% state of charge).  27.5 amp hours is not very much.  We would have to know how much amperage your computer charger pulls and how long it takes to recharge the computer battery.  We also would need to know the overhead on the particular inverter being used.  All inverter’s eat up a little bit of power just to run, in addition to the power inverted to whatever is connected to it.  Finally, we need to know if the battery will be powering anything else in the RV or if it will be solely dedicated to the inverter.  If it is powering anything else like lights or water pump or etc., that will also have to be factored into the power usage.  I suspect with the battery you describe, you would not be able to go a week between recharges.  

[RV_]

Felipe,

Disregard the warning. Chad, Felipe is in Chile and they use 220 as their standard voltage. So Felipe only needs to not mix US components and 220 power.

See here: https://www.bing.com/search?q=Chile+standard+voltage&qs=n&form=QBRE&sp=-1&pq=chile+standard+voltage&sc=0-22&sk=&cvid=B567F2796EF64F84B1E00DDACA7DC8B8

 

[Chad Heiser]

1 minute ago, RV_ said:

Felipe,

Disregard the warning. Chad, Felipe is in Chile and they use 220 as their standard voltage. So Felipe only needs to not mix US components and 220 power.

See here: https://www.bing.com/search?q=Chile+standard+voltage&qs=n&form=QBRE&sp=-1&pq=chile+standard+voltage&sc=0-22&sk=&cvid=B567F2796EF64F84B1E00DDACA7DC8B8

 

Ok, I was unaware he was in Chile. In that case RV is correct.  Disregard my warning in the first paragraph of my original response.  The remainder of my response still applies though.

[Felipe Blanco]

Thanks for tour replies, guys.

The macbook's power adaptor has the following information: 

input 100-240v 1.5A (1,50A) 50-60Hz FLEXTRONICS LPS

output 20.3V = 3A (USB PD) or 9V = 3A (USB PD) or 5.2v = 2.4A

I'm not sure what that means but I guess it can draw up to 3A per hour...? Chad, considering your numbers, I'd be able to charge the computer for about 7 or 8 hours considering the loss, maybe? When I charge the computer at home it takes about 1.5 hour to charge 100%. And no, the battery would not be powering anything else. That would be used exclusively for the computer.

Thanks!

[Chad Heiser]

From the numbers you posted, it looks like the charger draws 1.5 amps AC and converts it down to lower voltage and higher amps for the computer.  Assuming 1.5 amps per hour and 1.5 hours to recharge the battery in the computer, that is 2.25 amps coming out of the battery to get the computer recharged.  The inverter overhead is probably higher than that.  Without knowing exactly what make and model inverter it is, I will guess about 5 amps of inverter overhead per hour.  This is anther 7.5 amps to get the computer recharged.  That puts you at just under 10 amps per day with one and a half hours of usage.  From the battery rating you originally gave this will give you just under three days of usage before the battery has to be recharged (based on my assumed 5 amp of internal loss by having the inverter turned on and inverting).

[Lou Schneider]

Let me clarify Chad's excellent analysis a bit.

Amps is a momentary indication of current flow.  Amp-Hours are what's stored in a battery and is Amps X Time.  2 Amps drawn for one hour = 2 Amp-Hours.

So, assuming 1.5 hours at 1.5 Amps current flow, that's 2.25 Amp-Hours out of the 12 volt battery.   

Your 12 volt battery can provide 55 Amp-Hours so at first glance you should be able to get 20 days out of the battery.  But lead acid batteries don't like to be drawn down more than 50% of their capacity, so you actually have a 27.5 amp-hours of usable battery capacity.

If you don't use the battery for anything else, you should be able to get a week between chargings.

But why not connect it to the engine's electrical system so the alternator can charge it whenever the engine is running?  All you need is a relay that energizes when the ignition is on or an automatic battery isolator.

[Felipe Blanco]

Thank you everyone.

So I currently use a 90A lead acid battery for the engine. And there's another 70A battery under the driver's seat. The one I use for the engine is new, just bought it about a month ago, and the other one came with the RV, I don't know how old it is, but it's connected to the engine's electrical system so it charges with the alternator. I basically only use it for the LED lights inside the motorhome, the water pump and the boiler (only for the spark).

Yesterday I purchased a new 55A lead acid battery which I intended to use only to charge my laptop (not even my cell phone), because I thought that I would be able to charge my laptop at least 5 or 6 times for 1.5 hours before recharging but according to Chad I'd get maybe 3 days considering the inverter's loss (?) and that's is the part that I don't get and didn't take into consideration. Does this loss really affects that much the efficiency of the battery?

About connecting the new battery to the system, I thought of doing that but I was advised not to because it could overcharge the whole electrical system. Buy now I'm not so sure. When I use lights or the water pump, I'm actually drawing energy from both the engine battery (90A) and the one below the driver's seat (70A) right? Can I add the new 55A to this system and use the alternator to charge the computer? Would the alternator be able to handle all this?

Thank you again.

[Shawn Patterson]

Felipe,

A more efficient option would be to use a car charger instead of the standard wall charger to charge the laptop. Any time you go through an inverter there is a fair bit of loss.

I'm not a Mac guy, but something like this might be a better solution and maximize your battery.

https://www.amazon.com/gp/product/B071RDKSMJ

https://www.amazon.com/Chanzon-Cigarette-Terminal-Accessory-Inflator/dp/B07CQMQL9L

[Felipe Blanco]

Hey Shawn, do you mean a car charger that I can plug into the cigarette lighter?

[Lou Schneider]

6 hours ago, Felipe Blanco said:

About connecting the new battery to the system, I thought of doing that but I was advised not to because it could overcharge the whole electrical system. Buy now I'm not so sure. When I use lights or the water pump, I'm actually drawing energy from both the engine battery (90A) and the one below the driver's seat (70A) right? Can I add the new 55A to this system and use the alternator to charge the computer? Would the alternator be able to handle all this?

Thank you again.

Usually there is a relay or an isolator between the house and engine batteries so when the engine is running, the batteries are connected together and the alternator can charge both of them.

When you're stopped, the relay or isolator seperates the batteries so your lights, etc. only draw from the house battery.  This lets the engine battery stay fully charged to start the engine even if you fully drain the house battery.

An easy way to see if the batteries are connected together or if there is a relay or isolator between them is to disconnect the house battery.  If there are multiple wires on a terminal keep them together after you remove them from the battery.  Now see if your lights work with the house battery out of the circuit.  If they do, there is just wire connecting the house and chassis batteries.  If they don't, you have a relay or isolator.

I wouldn't worry about overloading your electrical system with the new battery - it's a non-issue.  Just connect the inverter and the new battery to your existing house battery.

[Felipe Blanco]

Hey, thanks for that, Lou.

I just did what you suggested and it turns out that the lights still work even though the house battery is disconnected. So I guess I don't have a relay or an isolator, or maybe I do but it isn't working. I will try connecting the new 55A to the system and see how it goes. Would it be a problem that this new battery is 55A, the other house battery is an used 70A and the engine is 90A?

Also, how do I connect this new battery to the existing house battery? Should I connect them in series or in parallel? I know I can find it on google but I need to know how exactly to look it up.

Thank you.

[Felipe Blanco]

I just read that I can wire two batteries in parallel if they have different amp hour ratings, deep cycle or regular. I wouldn't mix two different battery types like gel and lead acid though. I will want the batteries to be of the same type; 2 gel, 2 lead acid, 2 deep cycle and so on.

My new 55A says 'formula: silver, calcium and lead'. The older 70A has a user's guide attached to it and it says it's a lead acid one. So I guess they the same kind of battery and it should be ok to use both in parallel. Right? Or not?

I have already purchased the battery and I cannot return it so I'll keep it and it should give me more capacity for the house, even though the battery output will stay the same, correct?

Also, I wasn't thinking of doing this right now but I guess it's my best option. Go solar. i'm just trying to figure out if a 150w panel would be enough for me or if I should go for 200w. I'd be using it to charge my macbook pro 60w 3A, my 12v water pump 1.5A and a few LED lights.

Thanks.

[Chad Heiser]

13 hours ago, Felipe Blanco said:

Hey, thanks for that, Lou.

I just did what you suggested and it turns out that the lights still work even though the house battery is disconnected. So I guess I don't have a relay or an isolator, or maybe I do but it isn't working. I will try connecting the new 55A to the system and see how it goes. Would it be a problem that this new battery is 55A, the other house battery is an used 70A and the engine is 90A?

Also, how do I connect this new battery to the existing house battery? Should I connect them in series or in parallel? I know I can find it on google but I need to know how exactly to look it up.

Thank you.

When you did this test was the RV plugged into shore power?  If so, the converter would have been providing the power.  The test Lou described should be done with the RV disconnected from all external power sources so just the batteries are in the system.

[Kirk W]

16 hours ago, Felipe Blanco said:

Also, how do I connect this new battery to the existing house battery? Should I connect them in series or in parallel?

Parallel. In series, you double the voltage out.

[Felipe Blanco]

I did the test with the RV disconnected from all external power sources.

[oldjohnt]

17 hours ago, Felipe Blanco said:

I just did what you suggested and it turns out that the lights still work even though the house battery is disconnected. So I guess I don't have a relay or an isolator, or maybe I do but it isn't working. I will try connecting the new 55A to the system and see how it goes. Would it be a problem that this new battery is 55A, the other house battery is an used 70A and the engine is 90A?

Also, how do I connect this new battery to the existing house battery? Should I connect them in series or in parallel? I know I can find it on google but I need to know how exactly to look it up.

1) Felipe, if unhooking one battery (subject to where disconnected and wiring)  OR the other still allows a certain load (like lights) to operate, the two batteries must be wired in parallel IE  EITHER can still power the lights. Typically a battery isolator may be installed between the engine battery and the house battery such that they are ONLY IN PARALLEL when the engine is started and/or a push switch is activated. If there's no isolation and disconnection if you're dry camping with no shore power its possible to discharge the engine battery. I do NOT recommend house and engine batteries be permanently in parallel.........

2) Its BEST if all batteries in parallel are the same size and type and design and even age etc etc to achieve the best load and charging balance HOWEVER things will still "work" even in an imperfect situation.

3) You would connect the same voltage batteries in PARALLEL + to + and - to -...……….

17 hours ago, Felipe Blanco said:

My new 55A says 'formula: silver, calcium and lead'. The older 70A has a user's guide attached to it and it says it's a lead acid one. So I guess they the same kind of battery and it should be ok to use both in parallel. Right? Or not?

I have already purchased the battery and I cannot return it so I'll keep it and it should give me more capacity for the house, even though the battery output will stay the same, correct?

Also, I wasn't thinking of doing this right now but I guess it's my best option. Go solar. i'm just trying to figure out if a 150w panel would be enough for me or if I should go for 200w. I'd be using it to charge my macbook pro 60w 3A, my 12v water pump 1.5A and a few LED lights.

1) Again they will still "work" in parallel even if its NOT the best engineering or ideal situation

2) YES as you connect more batteries in parallel the total amp hours of energy storage is additive even If charging and load balance isn't the best.

3) You may as well use 200 watts while you're at it.

BOTTOM LINE  Its "best" if batteries are the same type and design and brand and age and things will still "work" even if not but proper load and charge balance isn't gonna be achieved. Its also good to use a battery isolator between house and engine batteries so when dry camping you're not drawing down the engine starting battery. Its best if house batteries be true Deep Cycle type while the engine battery is typically a starting battery...……..

 

John T

[Ray,IN]

On 3/5/2019 at 10:03 AM, Felipe Blanco said:

Hey Shawn, do you mean a car charger that I can plug into the cigarette lighter?

Look on line for a car charger for your laptop. Today's new vehicles even have a USB port on the dash to re-charge cell-phones. laptops, in addition to a cigar lighter outlet.