# Battery sizing help?

Discussion in 'General Technical Questions and Answers' started by N8MLP, Nov 5, 2018.

1. ### N8MLPHam MemberQRZ Page

I have a Icom 2200h collecting dust. With its high power output I thought maybe it would be good for off grid portable 2m work.

It is max 65w 15A, what mAh battery do I need? I have a feeling with that power draw it would be to large to backpack with.

2. ### VE3CGAXML SubscriberQRZ Page

it depends on the battery type but mainly how long you are going to operate say 12v at 15A.
go to this site and have a read https://deepcyclebatterystore.com/calculate-battery-amp-hours/
for your application I'f suggest VRLA or lifepo4 batteries.

weight may be an issue for you. heres a comparison between the same battery rating I got off an amazon.com search (sort of like scooter batteries)
VRLA 12v/20ah Dimensions: 7.13 L x 2.99 W x 6.54 H Inches Weight: 13.125 lb(s)
and a
LIFEPO4 12v/20ah 7.2 in. x 3.2 in. x 6.7 in 5.8 lbs.

the lifepo4's are lighter, this site here https://offgridham.com/2016/03/about-lifepo4-batteries/
has some info on them

did a search on LIFEPO4for portable ham ops and got some good google returns
heres one http://oh8stn.org/

3. ### AF7TSHam MemberQRZ Page

Battery size is set by two factors: ability to deliver the necessary power for the job, and ability to deliver the necessary energy for the job.

Batteries are described using 'amp hours'. This unit of measure means the amount of current that the battery can deliver (measured in amps) times the duration of the delivery (in hours). (Of course you can use different related units, eg. milliamp hours or amp seconds; simply scale appropriately.) The delivery starts 'fully charged' and ends at some definition of 'depleted'. Usually 'depleted' is defined in terms of minimum output voltage.

You might think that if a battery could deliver 1 A for 20 hours (20 amp hour rating) then if you need 20A the battery would deliver it for 1 hour. Unfortunately this is not correct. Batteries have internal impedance which means that the output voltage is lower when you draw more current. At higher discharge rates more energy is being dissipated heating up the battery itself, and you hit your minimum output voltage with fewer amp hours delivered.

For lead acid batteries, you are probably looking at an 'amp hour' rating at least 3 or 4 times larger than your maximum current draw in order to deliver sufficient voltage do your load and have a reasonable operating time. Probably 20-30kg for a 15A load. https://media.digikey.com/pdf/Data Sheets/Panasonic Batteries PDFS/LC-X1265P.pdf

Other battery technologies have lower internal impedance, which means that you can get away with a lower nominal amp hour capacity to run a heavy load. This is especially beneficial if you are only transmitting for a small fraction of your total operation.

73
Jon
AF7TS

4. ### WA4ILHSubscriberQRZ Page

You might consider also using a solar panel along with the battery if you are considering going off the grid. I played with a couple of these several years a go and was suprised how much power a solar panel produced in bright sunlight.
Tom WA4ILH

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5. ### N3HGBHam MemberQRZ Page

You don't HAVE to use 65 watts

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6. ### KF5LJWHam MemberQRZ Page

Anything you take off grid is going to cost you 5 to 10 times more than buying power from the POCO. So why do you want to pay so much for power? In battery cost alone is going to cost you \$1/Kwh. In TX I pay 7-cents per Kwh up to 2500 Kwh in a month, and anything over 2500 Kwh in a month the rate goes down to 6-cents per Kwh.

I design and install off grid solar systems for commercial companies like Telecom and Pipeline. They only use solar if there is no other choice even if it means it cost them \$100K to bring AC lines is far less expensive and a lot more reliable. Don't believe a word of Off-Grid Battery pays for itself, it just makes power a lot more expensive and makes you a very heavy polluter the Green Mafia will have you assassinated for.

7. ### W9KEYHam MemberQRZ Page

Might want to watch these West Mountain Radio videos for a few tips. I saw an updated presentation they gave at the HRO Superfest a few weeks ago, which also included information on LiFePO4 (lithium iron phosphate) batteries. http://www.westmountainradio.com/content.php?page=tutorials

They also have a Battery Capacity Calculator which is interesting, and does include Lithium battery suggestions: http://www.westmountainradio.com/content.php?page=calculators

Lithium batteries (versus Lead-Acid technology) maintain much "flatter" voltage discharge curves, meaning your transmitter will benefit from more constant / higher voltage (and therefore higher output power) for more time during the discharge cycle.

Since power required to transmit is much higher than to receive, the ratio of your time transmitting versus receiving will greatly influence the battery's total operating time. If you don't have suitable receive / transmit current measuring equipment, approximate values can be found in your radio's Specification Section. And as a previous poster pointed out - transmitting at reduced power output levels will certainly extend your total operating time.

Just remember - you must absolutely avoid over-discharging your battery (to prevent damaging it) - meaning you must know the battery's minimum recommended operating voltage, and cease operation before reaching that low level. Equipment is available from West Mountain and others which will monitor battery voltage and automatically turn off the system at a preset low voltage limit. Deep cycle Lead-Acid batteries are more tolerant of low discharge voltage levels, but Lithium's are not. To that end, some Lithium battery packs include a low voltage protection feature - see information from Bioenno Power.

(Disclaimer - I do occasional consulting work for WMR).

8. ### KD2ACOPlatinum SubscriberLife MemberPlatinum SubscriberQRZ Page

Because it’s there. You’re such a buzzkill.

9. ### KK5JYHam MemberQRZ Page

Expanding on Tom's idea -- if your plan is to run 2m "portable" from your vehicle, you could just connect the solar panel to the car battery and operate from it directly. As long as the panel can replace most/all of the energy you spend on the radio, you won't need a separate battery at all.

This is what I do when I am out doing railroad photography... I use a small solar panel to charge the car battery and run the VHF radio in the car while it is tuned to the RR frequencies. That way, the hours I spend parked with the radio running don't leave me with a dead battery.

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10. ### AF7TSHam MemberQRZ Page

Well, if you want to go portable then the extension cord can be killer.... Seriously, you make a very good point that 'off grid' is a huge waste of resources if you can reasonably connect to the grid. Even as a believer in the future viability of 'renewable' energy sources, I'd much rather have utility scale on grid solar than panels on my roof.

But batteries do have their place, and portable operation is one of them. In this case not only is a battery appropriate, but paying extra \$\$ for a light power dense battery also makes sense.

Going back to what the OP wants, a lead acid battery (cheapest in terms of \$ per stored kWh) probably doesn't make sense if the desire is to actually hike with the thing.

If most time is spent listening, then battery with solar might make sense.

Or perhaps once the mass of the battery is considered, it may make sense to ditch the IC2200H and instead use an HT with a better external antenna

73
Jon
AF7TS