I see this subject coming up a lot on QRZ and thought I would take a few minutes to speak to the subject. I have been in the Telco, Power Generation, and RF Communication sectors for some 33 years now as a Technician and Engineer. For the last 10 years I do a fair bit of design of Off Grid Solar Battery systems for the Telcos and Pipe Line industry. My experience has afforded me quite a bit of exposure to battery manufactures, R&D, and industry engineering, installation standards professionals. So with that said I would like to share what I know about batteries and how to integrate into ham operations.
In this discussion I will only address the Lead Acid chemistry because it is the most proven, mature, and affordable for ham operations. I know the Nickel and Lithium dominate the HT market, but I will not go into because they are very expensive and not appropriate to use in medium RF Power applications. So let’s get started.
BASIC CATEGORIES:
Lead acid batteries fall into 3 basic categories of
STARTING (aka cranking or starting engines),
HYBRID (Marine, RV, Golf Cart), and the true
DEEP CYCLE batteries. Do not confuse Flooded Lead Acid , AGM or Gel as they are all Lead Acid chemistry. I will discuss that in a moment. So let’s move on to the Pro’s & Cons of each category as it applies to the ham operator.
Starting-Cranking Batteries
Unless it is an EMERGENCY do not use Starting Batteries in the shack. It is that simple of a rule of thumb. Perfectly fine to connect your HF rig to in your auto, but do not bring them into the shack or field unless you have no choice or an emergency. The dead giveaway to a Starting-Cranking battery is it will have a Cold Cranking Amps (CCA) specification.
Starting batteries are designed with multiple thin spongy like plates to increase surface area and thus lower the internal resistance. This allows them to deliver very high short burst of current to crank an engine, and then be recharged quickly by the vehicle alternator. If pressed into cycle service will quickly deteriorate the plates yielding very few charge\discharge cycles. So only use in a pinch if you have to. Otherwise avoid using.
Hybrid (RV, Marine, Golf Cart) Batteries
Before I talk about true deep cycle batteries it is important to discuss the hybrid types because they are somewhere in between Starting and Deep Cycle batteries. They are designed with slightly fewer but slightly thicker plates than Starting batteries, but nowhere as heavy as true deep cycle batteries.
This design still allows them to deliver fairly high starting currents like a Starting battery and fast recharge because the internal resistance is still fairly low. It also allows them to be used for cycle service with mediocre results. When used in cycle service you can get up to 500 charge/discharge cycle proving you do not discharge them more than 50% DOD, more if kept to no more than 20% DOD before recharging. So they can be used, but do not expect then to last more than 2 or 3 years with TLC.
Again like Starting Batteries there is a dead giveaway spec of CCA, Marine Cranking Amps (MCA) Reserve Capacity (RC), and Amp Hours. You will see all or some of the ratings and will tip you off instantly.
Deep Cycle Batteries
OK this is what most of you are really after. True Deep Cycle batteries are designed with fewer but much heavier and thicker plates than their Starting and Hybrid cousins. The advantage is obvious at this point as the thicker heavier plates take much longer to deteriorate and thus afford up to 5000 Charge/Discharge cycles for the better made units like Rolls and Trojan RE line ups. The down side is the fewer thicker plates have a higher internal resistance and thus incapable of being used to start a motor.
The internal resistance is something you need to be aware of because it significantly affects the amount of discharge current the battery can deliver without significant voltage drop at the batteries term post. It also affects the charge current that can be used to charge the battery with. No worries as it is easy to determine minimum battery size based on the normal expected load current. In addition the maximum load current is the same as the maximum safe charge current. So here are the two rules of thumb.
- For Flooded Lead Acid batteries find the 20 hour discharge rate Amp Hour rating say 200 AH. The maximum charge and discharge current = C/8 where C = the AH rating. So 200 AH / 8 H = 25 amps.
- For AGM same as above except the formula is C/4. So a 200 AH AGM is 200 AH / 4 H = 50 amps.
Going back to Hybrid batteries for a moment I would like you to examine 2 battery specifications of the same battery made by Trojan. The first one is the
T-105 battery the standard for Golf Carts batteries. It is a 6 volt 225 AG battery at the 20 hour rate. Now look at the spec for the
Trojan T-105RE. Same BCI group GC2 case. Now look at the weight and what do you notice? The T-105RE is 5 pounds heavier because it have thicker lead plates and thus more lead in it. The T-105 is a hybrid battery which is marketed as a Golf Cart battery and could also me marketed as a RV or Marine battery. They only specify the AH capacity at various discharge rates from 2 hours to 100 hours to account for Peuket Law. See haw the same battery can be either a 146 AH to a 250 AH battery. That is Peukert Law applied.
Sealed Lead Acid vs Flooded Lead Acid
The lead acid chemistry batteries fall into two basic types of SLA and FLA. Of the SLA types break down into two sub categories of Absorbed Glass Mat and Gel. Gel will not be discussed because they simply should not be used because they are just too sensitive to overcharging and other abuse.
FLA is the preferred choice for many reasons. FLA is very tolerant to overcharging and almost impossible to run into Thermal Runaway. FLA will also yield the highest number of charge-discharge cycles, and the least expensive. FLA can also be equalized when the Specific gravity falls out of range by applying a Equalizing Charge. The down side to FLA batteries is they do require some maintenance like checking the specific gravity and adding water from time to time. Additional the max charge discharge rate is limited to about C/8.
AGM batteries has useful applications like in extreme cold environment below -40 F, unusual orientation like on their sides, and are portable. Additionally AGM has lower internal resistance which allows the maximum charge discharge rate of C/4. The down side is they are expensive (about 100% more than FLA), specific gravity cannot be measured or corrected by an Equalizing Charge. Lastly they will not last as long as the FLA.
Charging and Application
I will keep this simple as I can. One of the best applications is operating when commercial power fails. The easiest way to use them is float right off the ham shack DC power supply. In most applications no modifications or equipment is needed. Just connect them right up to the DC power supply like your radio. Doing it this way and Floating them keeps them ready to go and just waiting for the power to go out.
Now you do have to make the correct battery selection and set the voltage of your DC power supply to the manufacture Float Voltage recommendation. Sizing is easy as I explained earlier uses the C/X rule. For example you have a 30 amp DC power supply and will use a FLA battery. The minimum size battery is that can be used is C/8. So with a 30 amp supply you would select 8 x 30 amps = 240 AH. The highest you want to go is C/12 or 30 amps x 12 = 360 AH. The reason on the upper limit is FLA batteries will stratify (Acid will sink to the bottom of the jar) if not charged at a high enough rate. A C.12 charge rate will cause the batteries to bubble thus string up the electrolyte.
For AGM the minimum size is based on C/4. So that same 30 amp power supply the minimum is 4 x 30 = 120 AH. On the high end you can to up to C/20 because AGM batteries cannot stratify. So 30 x 20 = 600 AH. Don’t go over C/20 because then recharge times are just too long.
Cycle Life
Need to spend a minute on this. The best way to extend your your battery life is do not over discharge your battery, recharge it immediately, and never let it sit in a discharged state. OK there is a relationship of Depth of Discharge (DOD) vs Cycle life. Th edeeper you discharge your battery, the fewer cycles you will have. As a general rule do not discharge your battery more than 20% and never every discharge it more than 50% ever. Go back to the T-105 and T-105RE spec and scroll all the way down to the last page and look at the Discharge vs DOD graph. The T-105 is as high as 3000 cycles at 20% DOD, down to just 500 cycles at 100 % DOD. On the other hand the T-105RE is as high as 4000 cycles @ 20% DOD down to 700 cycles @ 100% DOD. FWIW the graphs clearly demonstrates the difference between a hybrid and deep cycle batteries.
Well I hope that was helpful, and I will be happy to answer any questions or expand if needed.
Battery Tutorial and Discussion
Originally Posted by K8ERV
