Advice on battery needed

wu9b Registered Users Posts: 3
I am considering the purchase of a pair of Interstate Marine/RV Deep Cycle (Group size 27DC) batteries to run a baby off grid 100 watt ham radio station. (100 watts only on transmit; 12 volt radio with one amp on receive and 18 amps or so on transmit. I would only transmit at part time even on a busy contest and usually the radio would never be used more that 10-12 hours even on a contest day)

I found these batteries at my local Costco. My research indicates that these are built by Johnson Controls which I believe makes a good battery. They have a 750MCA / 160 RC rating but I don see a KWH rating anywhere and I have checked their web site too. So I am wondering if anyone who reads this are familiar with these. Are they reliable? Is it OK to use these indoors in a well ventilated room? Should I bag that idea for a single AGM battery? I like the idea of having the battery (batteries) indoors as I live near Phoenix. I think I would remember be more diligent about checking fluid levels if they are indoors.

I plan on charging these batteries with 4 New Old Stock Photowatt panels PWX500 (17V@3 amps typical) using a Trace/Xantrex C40 charge controller. All of these components are in fine working order. I think this should run the radio and a few minor accessories and low voltage lighting just fine, even if I have a few cloudy days. (Any advice on lighting? 12v LCD/LED???? or whatever.)

Thanks for reading this and thanks in advance for your advice!

Steve WU9B


  • Windsun
    Windsun Solar Expert Posts: 1,164 ✭✭
    Re: Advice on battery needed

    A group 27 battery typically has around 80-95 amp-hour capacity. So assuming you are using 1 amp 90% of the time and 18 amps 10% of the time, you would use around 11 amp-hours (rcv) + roughly 25 amp-hours (xmt), so actually a single battery would probably work, but would be marginal if you transmit more than 10% or so. You could also go with just a couple of 6 volt golf car batteries in series for around 220 AH.

    If the panels are all in use when you are doing this, a single 90 AH or so battery should work fine.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Advice on battery needed

    windsun did hit on this, but i will emphasize that this will not be suitable for contesting as you will put high tx loads to the batteries in the 35%-45% cycle range and the operating times would get extended too making things worse. also, you don't want to tax your batteries beyond 50% dod as that will cut into their cycle life more and if far enough it could damage the batteries.

    another note is that the 4 pvs will (my typo corrected:cry:) maximally output 12a, but will typically be far lower and we use 77% for that as a generic figure. you are now into the 9a area and any extra losses could deplete the charge further as well. this will most likely be good for about 5hrs of full sun giving you about 45ah. you know enough of electronics to know that radio could eat that up in no time.
  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    Re: Advice on battery needed

    AND, furthermore, many, many HF 100 Watt radios do not work well on a battery that is not being charged .. ie, most of these radios are looking for 13.8 V DC to meet the specs. A loaded battery that is not being charged by a capable charger will have a terminal voltage around 12.2 ish volts even when fully charged. This voltage will sag even more as it is used. Usually the result is disappointing. GL, Vic K6IC
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.