Amp Hours and Usage Clarification

[Rjhdog]

Hey folks,

I have researched this a bit and wanted to make sure I understand this correctly.

If I have a 50 amp hour aux battery and my LED string lights draw 5 amps. Can I simply divide the two and expect roughly 10 hours of battery use?

Also, can anyone give me an idea generally what a standard Stereo draws? I know there are lots of variables with speaker size, headunit type, etc. I am just looking for a rough estimate to get an idea of battery usage.

thanks!

[Abscate]

Standard stereo, 30 watts. Big one can be 3x that.

You should not run a lead acid battery below 1/2 capacity, so 5 hours use of that load would be reasonable.
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[Syncro Jael]

Yup but your battery would be dead.
You should never take even a deep cell battery below 50%. They just will not last very long.

Take a look at this site. It will answer your questions.

My Pioneer draws about 2amps. But again it depends on volume, speakers, subs, and if you are running an amp.

http://www.powerstream.com/battery-capacity-calculations.htm
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[Altoona]

Also, note that the rate at which you draw affects the calculation.

For instance (and just for arguments sake), a 50 Ahr battery could theoretically supply 1 amp for 50 hours. But if you draw 10 amps, it won't last 5 hours, more like 3-4 hours. Again, these numbers are purely theoretical, it is the theory you should be aware of - the higher the draw, the faster your battery is drained, over and above what the numbers would suggest.

[nocreditnodebt]

The Standard measure of capacity is the 20 hour rate.

A hundred amp hour battery can provide 5 amps for 20 hours before becoming fully 100% discharged at a measured 10.5 volts.

Loads under 5 amps and the hundred amp hour battery has a bit more than 100 amp hours to give. Loads over 5 amps reduce the overall capacity the battery has to give. The higher the load, the less overall capacity the battery has to give.

So the 20 hour rate on a 50 AH battery would be 2.5 amps. When fully charged, and healthy, the 50 AH battery can provide 2.5 amps for 20 hours until being considered fully depleted at 10.5v. Amp loads over 2.5 amps will make the battery have smaller overall capacity.

So you can't just do simple math, unless the loads you are using match the amps used to figure out the 20 hour rate.

Lead acid batteries can be taken below 50%, but this causes them to age faster, and of course a full recharge ASAP after any discharge will prolong battery life.

You do not want the battery to stay 80% or less charged. If cycling it daily to 50%, on day 14 or so, you must recharge to a true 100%, and this takes many many hours at voltages in the mid 14's to achieve.

If the 100% recharge is not done, the battery quickly walks down in capacity and becomes even more petulant and requires even more effort time and voltage to return to the remaining maximum energy density.

Lithium batteries will one day become affordable enough that we need not worry about top charging and fully charging them after each discharge cycle, but as long as lead acid battery is your electrical storage medium, you either need to resign yourself to replacing batteries more often, or resign yourself to learning how to, and acquiring the proper tools, to actually fully recharge them, promptly and properly, just to get a respectable lifespan from them.

Unfortunately many automatic chargers do not do a good job of getting the battery truly fully charged, unless the charger has a float function and the charger is left plugged in for many days after the full charge indicator is initially illuminated.

Stereo consumption depends on many factors including volume and the amount of bass in the music you are listening to.

Mine claims 52watts x 4, and at full volume, it does actually come close to that amount of electrical consumption. Turned on at very low volume it is about 0.9amps. Chilling volume, not enough to disturb neighbors 20 feet away, about 1.4 amps. Running the CD player draws ~ 0.5 amps more than running my MP3 player through the AUX port.

On an older stereo, I thought I'd save battery power by fading my speakers to my smaller rear speakers, but was dismayed to learn later that the amp draw was the same whether the 6x9s were faded out or not When faded, the head unit just produced a lot more heat.

Not sure about my newer stereo. Can't really test right now as the neighbors kid is asleep.

[ThankYouJerry]

[Rjhdog]

Hmmmm,

Looks like my battery choice of 50aH is rather limited. At operating around 2.5 amps max for ideal battery efficiency it looks like the stereo w/o sub and oem LED lighting will be about all I should run...

Man, I just bought the battery and my led strip lights.

I don't have the camper so fridge and sink are not a worry.
I was planning to run the stereo, oem interior lighting, map light, a couple 12v & dual usb connectors, as well as Led strip lighting on the Aux with a SurePower 1315.

According to the Led multi color Strip specs :
I will likely run just one color at a time and will possibly dim it so my draw is more closer to 1.5 amp for color and up to 2.5 amp for white. Max ( no dim)

If my stereo is close to "Nocreditnodebt" (above) at 1.4 max. Then my range under normal camping conditions will be around 3 - 4.5 on the highest if all is on at same time.

Realistically, the lights will be on just a couple hours in the evening. Stereo plays an hour or two at dusk. They won't be on at the same time all the time. Then the occasional charging of an iPhone and turning on the oem lights occasionally to see in the cabin.

I currently use the rig as weekend warrior with a few longer (5+ days) camp adventures.

I am leaning towards that this setup could work for me just fine. Even if I did use upwards of 3-4.5 amps sometimes, what life expectancy drop are we talking? And how harder will it be to charge?

Also, does the Surepower set up help with these conditions if I turn the rig on and move to different campsites, etc?

[Howesight]

Batteries do have to have a basis enabling comparison and as one poster said above, the 20 hour standard is the most widely used.

Here's a few important pointers for now:

1. Get an adjustable alternator voltage controller:

http://vwparts.aircooled.net/Adjustable-Voltage-Re...ulator.htm

The reason is the stock alternator regulator sets the voltage far too low (13.2 to 13.4 volts) for effective battery charging, both starter and house battery.

2. Note that 50% discharge is the accepted norm for reasonable battery life. That 50% is signified by 12.2 volts. Note that both immediately after charging and immediately after discharging, a lead-acid battery will read high and low respectively until the battery "stabilizes". That takes about an hour and the measurement has to be done with no draws on the battery. So, you can test by running your various draws, turning them all off, and measuring voltage after an hour. If you are at 12.2 volts or more, you know the real-world behaviour of your system allows those draws. If not, you can then adjust your draws accordingly.

3. Having said that, the reduction in battery life caused by discharging a deep cycle more than 50% can be significantly mitigated by commencing charging ASAP after the discharge occurs.

4. I use a NOCO Genius G7200 and recharge right after a discharge when I get home. (My Subaru engine alternator puts out 14.4 volts, which is not bad, but unless I run the engine non-stop for 3 to 6 hours, depending on vehicle draws like lights, defroster, etc, it will not refill a 12.2 volt battery).

5. I also do an equalization charge (at over 15 volts) once a month on the deep cycle using the NOCO.
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[nocreditnodebt]

A little clarification. I said at easy listening volume, mine draws about 1.4 amps. If I do crank it up to near maximum it does draw about 10 amps and more if there is a lot of bass in the music.

This is just a Sony head unit, no extra amps or subwoofers.

Amp draws over 2.5 amps can be calculated with a Peukert number calculator.

A 50 AH battery under a 10 amp load becomes a 39.17 AH battery. That is with a new healthy fully charged battery. When batteries age their peukert number increases to 1.3 or so( from 1.1) and at 1.3, the 50 AH battery only has 25 AH capacity to provide at a 10 amp rate.


http://www.csgnetwork.com/batterylifecalc.html

And waiting 1 hour for voltage to rebound after removing a load will be more accurate on a new healthy battery than on an older abused battery. It will be different depending on how big the load was, the battery temperature, the battery construction and design. The longer you can wait to take a voltage reading the more accurate that the rested voltage will relate to state of charge.

Also while 12.2v is a good average number for 50%, batteries vary fairly widely and 12.2v cannot be said to be the true 50% point for every battery.

Helps if the battery manufacturer can be determined and if they have published specs as to what rested voltage represents 50%, as I've seen ranges from 12.06v to 12.31v being the 50% mark.

[HackAl]

This is a very informative thread and I wish I read it before installing my setup last year. (Gowesty kit with two 22ah batteries under driver's seat). The kit came with the van when I bought it but I installed it. It worked fine but I ran it down (way past 50%) on more than one occasion. I didn't immediately recharge and now those two batteries are pretty well spent.

My new stereo usage accounts for the bulk of the depletion, I would imagine, then charging two cell phones, sink, dome light, etc.

The 50ah lithium-ion battery looks pretty sweet but I can't see the $500 outlay so I'm going to ration my power usage better. As cool as solar would be, I don't camp enough to justify that outlay either but I would consider a simple, smaller set up.

I may just order 3 more 22ah batteries and meter for the cigarette lighter and not let it dip past 12v. Before I do that, I am curious about what others are doing on a budget to have a modest amount of power for the 2-3 night camping trip.

So for 66ah (effectively 33ah for 50% depletion), could I run the stereo (Pioneer mech-les, no amp, 4 small speakers for 3 hours) and fully charge two cell phones one time each)? I'm struggling to determine how much power I "need". (I'm also learning to put phones in power-saving mode which also works great).

Thanks for any guidance.
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[Ahwahnee]

[davevickery]

I have one of these.
https://www.amazon.com/Innova-3721-Battery-Charging-Monitor/dp/B000EVWDU0

There are many brands but this is nice because it goes to 2 decimal places. I found 1 decimal place was not accurate enough sometimes. When I plug into the front, I can see charging voltage. If I see it hit float charge, I know my batteries are completely topped up. When plugged into a rear outlet I can see how the house battery is doing. It may seem like it doesn't tell you much, but you get very sensitive to the readings mean even if with things running. Generally if I see 12.0 Volts with my heater running, I know I am at at about 50% discharged. If I shut off the heater, the battery will stabilize at around 12.2. I've checked it enough, that I now know what it different voltages mean with or without a load.

I also run the van for a little while in the morning if I wake up to low 12s voltage. It bulk charges when it that low so it puts a good amount of juice back in quickly.

I have 135 Amp Hours combined between my starting and house battery and I usually just leave them manually connected. The heater will shut itself off from low voltage before the van won't start even if I wasn't paying attention to the voltmeter. So I have a usable 65 Ah bank. I have 2 AGM batteries, so I don't mind keeping them in parallel. With them I can go 3 days and just run the engine a little bit if I am not moving around. And I may have to not run the heater continuously while sleeping. When I get home after running them down to 50% I always plug in the shore charger.

I don't even consider LED lighting in my calculations. It is a tiny draw even when run for hours every night. And charging any USB item is also next to nothing. Usually they are plugged in while driving and only plugged them in while camping if they are getting run down, usually my tablet. I think it only uses 1 amp as the charge port is rated 2 amps at 5 volts. I have used the stereo enough to drain my batteries but that was playing it loud with the doors open for hours every day while hanging around camp.

If I got a DC fridge, I would add a solar panel. Around here, solar works good and provides good power when the fridge is working the hardest. The heater not so much.

[DanHoug]

[davevickery]

[SSWesty]

There have been a few of us that have tried using 2-4 of the 22ah batteries and we've learned it doesn't work out that great. When one battery fails it strains the rest of them, then if you replace the bad one with a new one your batteries get mismatched. It's usually a good practice to not mix old and new batteries together. So I'll throw in a vote for going with one battery solution.

A little clarification on your usage would help, do you go for 2-3 days and stay in one sport or do you drive the van any when you get to your destination? If you are sitting without running the engine then we need to calc usage for 3 days and no replenishment until your drive home. However if you do drive around at your destination that helps to recharge.

Second we need a better idea on your amp draw per day and what your stereo draws. If it's an old school car stereo I think they are about 1.5 amps however some of the newer ones with the pop up screens will draw more. Also varies if you are using a CD player vs. just the radio.

A list of how many hours you run stuff would help, here is an example.
Stereo - 6 hours x 1.5 amps? = 9 amps
Lights - 2 hours x 2 amps? = 4 amps(need to know draw on your lights)
Charge Phones 2 phones x 1.5 amps = 3 amps
Pump should be less than .5 amps

So for this hypothetical day you'd use 15 amps with the majority of it being the stereo. So if you sit 3 days with the engine off you'd need about 90 amps of capacity which equals a pretty big battery like a group 24 deep cycle battery.(3 days @ 15 amps = 45 amps / 50% discharge amount of battery = 90 amps)

I use a 44 amp battery and this is what my usage looks like:
Lights in summer 2 hours x 1.5 amp = 3 amps
Propex heater if it's chilly 1 hour x 2 amp = 2 amps
pump and charging something that's low 2 amp

I am using 7 amps a day so I am okay to sit for 2-3 days before needing to charge. If it's warm out and I am not using the heater then I am down to 4 amps a day which is basically nothing.

One other item to investigate is the size of the wire that charges the house battery. The kits like the GoWesty one use to use a pretty light wire for charging. This means your house battery may be slow to charge back up.

[HBB]

[HackAl]

SSWesty, we typically stay in one location and don't drive around. The 15 amp scenario you described sounds about right. I guess we are bigger hogs than we thought. That said, we'll learn to conserve power to the extent we can get it from a battery(ies) that fit under the driver's seat. If not, we are just trading a power problem for space problem because all other cabinets are strategically full.

I'm guessing 50ah is the biggest we'll get under the seat. Gowesty's perpetually sold-out 50ah battery is 7 ¾" W x 7" H x 6 ½" D. I'd prefer one battery as well, though I'd have more power with two 30ah in parallel.

Dave, your recommended power charging monitor is in my Amazon cart. Having a hard time trying to find a battery on Amazon that will fit, for sure, under the seat. How's this one: https://www.amazon.com/ML50-12-Replaces-Power-Patrol-SLA1161/dp/B00NINUS6M (At least one user says it would fit.) Wonder if I'm taking the seat out.

(Edit: Found the user on the Samba. I'm taking out the seat: https://www.thesamba.com/vw/forum/viewtopic.php?t=...p;start=0)
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[davevickery]

[SSWesty]

Interstate Batteries handles a few sizes that will fit under the seat. New batteries are sometimes bad and they can load test a battery before you buy it.

If you can figure out your stereo draw that would be a good piece of information. Even a cheap volt meter from harbor freight will tell you the amp draw on stuff that pulls less than 10 amps. If the stereo is only drawing .75 amps you'd be in better shape for a 3 day outing.

If you are consuming 15 amps a day you could augment with a small solar panel that lays on the dash. Picking up 5 to 10 amps would be a big help.

[HackAl]

That's interesting. Something like this, maybe: http://www.gowesty.com/product/solar/24672/21w-mini-folding-solar-panel

My stereo: https://www.pioneerelectronics.com/PUSA/Car/Digital+Media+Receivers/MVH-X390BT (50W x 4). My speakers: https://www.amazon.com/gp/product/B00399HKIY/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 (110 Watts Max. Power)

I have a multimeter and will try to get a better handle on that tomorrow.

I wish there was someplace around me that had the right size battery that I could test before purchase.
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