Friday, January 27, 2006

More batteries

I got a whole boat load (well, trunk load really) of batteries from a friend to test. He inherited them from someone who moved out of state and didn't want to take the whole load with him. There are some that are unused (still in their original boxes). I calculated that on the way home, I had 800 Amp Hours of 12 v power in the vehicle. That would have been at full rated capacity of course. These are all AGM batteries (like this one) that were either used or destined for use in wheelchairs.

Anyway, the first couple I tested were not so good; they are rather old and had been in use for quite some time (one was dated 1998). These 70 AH rated batteries topped out at 30 and 50 Ah after three cycles of charge/discharge.

Next, I tested (well, I'm still working on them) two of the "unused" batteries. They look fairly new, but I can tell that they've been hooked up to something before - even if only for a short time - because of the marks on the terminals. These two are doing much better! I charged one of them up partially (using my new Schumacher WM-2500A charger). The first time around it tested at about 50 AH. On the next cycle after charging it fully, it was up to 67 AH under a 0.1C load (this is actually its rated capacity - 75 AH * 0.9 = 67.5). On these big batteries, 0.1C is about the highest load I can use on my tester.

The second "unused" battery is undergoing its second test. I charged this one up completely for its first test and it measured 63 AH. The trace on the current test is running somewhat higher than the first one so far, but I'm only about 10 AH into it.

I'll probably cycle these two batteries one more time after this to see if they continue to improve significantly.

Interesting notes:

  1. I learned from the spec sheet I listed above that they recommend a maximum 15 AH charge rate. I had read elsewhere that you can use a rate up to 40% of the rated capacity of the battery. This was why I selected the 25 AH charger to begin with for these 70-80 AH batteries. It's not that big of a deal to use the 12 AH rate; it still takes overnight anyhow. I like having the capability of getting a battery (or multiple batteries) charged up quickly if need be...
  2. Even though a charger is rated at 25 Amps, you can't charge a dead 75 AH battery in 3 hours. It takes overnight or so (each battery is a little different) for it to absorb that last 10% of energy before it's "fully charged."
  3. My fancy new charger does a few cool things to keep the charge rate up. Initially, it hits the battery with as much current as it can while keeping the voltage under a certain level (it seems to use about 15.5 volts or so). This seems high, but it only does it for a short time to gauge the battery. Then, it just dumps as much charge into the battery as it can (it peaked at 30 Amps according to my Whatt Meter in the 25 Amp mode) until the voltage nears the maximum for whatever battery type it's charging. It tapers off until the voltage tops out at whatever its cut-off voltage is and it goes into "float mode" (where it seems to hold at about 13.8 volts - which is perfect for AGM batteries). This taper period is why the charge takes longer than just Capacity / Charge Rate. On batteries that are badly sulfated (at least I think that's why it was doing it in one of these batteries), the voltage quickly goes high and the charger went into float mode. It was putting 2.5 Amps constant into the battery for several hours before it tapered again and then started cycling up and down to a maximum of several hundred milliamps while holding at 13.8 volts.
  4. The "float mode" of this charger is really a cycle where it raises the voltage to 13.8 volts and then shuts down until the voltage drops a few tenths of a volts and it ramps back up again. It does it quickly so it's hard to get a good reading on my digital meter.
  5. Because of this pseudo float mode, getting the battery completely and fully charged would take quite a while on this charger. I would say that charging it up most of the way with the fast charger and then putting it on a power supply (like a UPS or a Ham Radio supply) that holds a constant voltage is a faster way to get a full charge.

Monday, January 23, 2006

UCARES Training Item

Training Item given on the Utah County ARES net on 23 Jan 2006
(It was originally scheduled for 17 Jan, but was delayed a week)

[2006-02-03 Note: Eric Harrison KE7BQE send me an e-mail saying that he recorded the net and has posted it here: Thanks Eric!]
I’ve played a lot recently playing with batteries and I thought I’d talk tonight about some of the many types of batteries we may encounter in the Amateur Radio world, and I’ll briefly mention a few of their characteristics.
First, the standard non-rechargeable types everyone has used are of course the Alkaline batteries that we get from the grocery store. These come in all sizes from N to D. One of the most important attributes of Alkaline batteries in Amateur Radio or Emergency Communications situation is that they are available almost anywhere. I’ll come back to this point later.
Non-rechargeable lithium batteries are widely available in 9v, 123 and AA sizes. Some of the advantages of non-rechargeable lithium batteries in commonly used sizes are that they are lighter than akalines and they last longer in devices like GPS units, flashlights, digital cameras, and so forth. Hikers, cavers, and others are often willing to pay a little extra for these high-performance batteries.
Rechargeable batteries in commonly available sizes come in two main chemistries, Nickel Cadmium (also referred to as Ni-Cad) and the newer Nickel Metal Hydride (or NiMH). A key advantage of rechargeable batteries over alkaline is that they cost less for the power that they provide over their lifetimes.
Rechargeable battery packs for Hand-Held radios come in three main types, NiCd, NiMH, and the newer Lithium based chemistries.
Other types of batteries I’d like to include as useful to Hams tonight are Lead Acid batteries. Car and Boat type Lead Acid batteries are most often the Flooded Electrolyte type (they have liquid that sloshes around inside them which can spill if they are tipped over). Sealed Lead Acid batteries – the kind that Hams like to carry around – don’t spill if tipped over and are often used in things like wheelchairs, electric scooters, those cordless 20 trillion candle-power spotlights, and so forth.
Rechargeable NiCd batteries have been in use for over 60 years. Sealed Lead Acid batteries have been around for 30-40 years. NiMH and Lithium-Ion batteries became widespread in the 1990’s. The new polymer based lithium batteries are barely 5 years old. And more types are coming I’m sure.
So now that I’ve mentioned a few different types of batteries, I’d like to talk a little about the advantages, disadvantages and care of each type.
First, back to the point I made earlier about batteries you can buy at a grocery store. If your equipment can run from these types of batteries, you will have a very good chance of being able to borrow some spares from someone else if yours happen to go dead sometime. Whether it’s a public service event or an actual emergency you will probably be able to get AA size batteries. While I have not always been completely successful, I have made an effort to make sure that all of my portable emergency communications gear can run from AA sized batteries. This way I don’t have to carry separate sets of spares for each device and my radio can share batteries with my flashlight if the need arises.
A little now about rechargeable battery packs like the ones on most handheld radios. I’m going to be fairly simplistic here as there is quite a lot of science behind these packs and yours may differ or contain a new technology or whatever; so IN GENERAL here are some tips to help your battery packs last longer and give you the most operating time per charge.
If you have a Nickel based pack (NiCd or NiMH), run it down at least every 5-10 times you charge it. If your radio automatically shuts itself off when the voltage drops too low, you are better off than some of us who have Kenwood radios that don’t do that. Some radios really will run a battery pack down completely – all the way to 0 volts if you let it go that far. This is particularly bad because a battery pack is typically made up of multiple cells. Running the pack completely dead will most likely damage one or more of the weaker cells inside. In short – run it down, but not dead every 5 to 10 times you charge it.
If you have a lithium based pack, charge it at any and every convenient time. Lithium based batteries do better if they are discharged partially and recharged multiple times than if they are completely discharged on each cycle. Lithium batteries will die within a few years whether they are used or not. Their chemistry is such that they are on a downward slope from the day they are made. Lithium packs cannot be charged with chargers that are not specially designed for charging them.

Cycling either Nickel or Lithium based battery packs in hot environments significantly shortens their lifetimes. Cycling them at 85 degrees, will reduce their life by about 20%, and their life may be reduced by as much as 40% at 100 degrees. That doesn’t mean that you will get less talk-time if you charge a battery while it’s at 100 degrees, it just means that you won’t be able to cycle them as many times. Sitting a radio on the seat of a car in the summertime and charging the battery pack while it’s at 120 degrees is hard on the pack. Some smarter battery chargers won’t even start to charge when they detect too high a temperature.

Sealed Lead Acid or SLA batteries, like Lithium based batteries, do great when they are charged as often as possible. Unlike the other types, SLA batteries do great when they are left on float chargers that are designed specifically for them. Unfortunately, car or boat float chargers, or motorcycle battery chargers are not designed for use with Sealed Lead Acid batteries. Let me repeat this in stronger terms. Hooking an SLA battery to a float charger not designed for an SLA battery could destroy the battery in a relatively short time. Most of the power supplies that we use with our Ham gear can (and often do) provide the perfect voltage for floating SLA batteries. However, caution is in order here in case you’re thinking of hooking up your battery to your power supply. Most power supplies are not designed as battery chargers and they may not work well if you try to hook up a battery (especially a discharged one). In this situation they may simply shut down if they have over-current protection built into them. If they don’t have this protection, they may blow a fuse or they may liberate some of their carefully stored smoke. Also, if you turn the power supply off (or lose shore power) the battery may be completely drained. I have found that a really great way to keep my SLA batteries charged and ready to go is to hook them up to a computer UPS. Most UPS units have chargers in them that are designed for use with SLA batteries (since they have batteries in them). I’ve got some pictures and other notes about doing this on my web log ( I’ll post a link to the site on the page as well.
The last thing I’m going to talk about is Self-discharge. Batteries that are left disconnected discharge slowly. For non-rechargeable lithium batteries the self-discharge rate is very low. They will easily last 10 years with only a small loss of charge. That’s why these batteries are so good for long term storage or very low drain devices like clocks and smoke alarms. Alkaline batteries can be good after several years of sitting around too – just check the dates they print on them nowadays. However, at the high temperatures encountered in hot cars even Alkaline batteries can lose half of their charge within a year. Nickel based rechargeable batteries have a much higher discharge rate of 1-2 percent per day. NiMH batteries can lose 10% in the first 24 hours and then another couple percent per day at room temperature. After a few weeks in a high temperature environment Nickel based batteries may be completely drained due to self-discharge. Lithium based rechargeable batteries fare much better than other rechargeables and only self-discharge at about 2-3% per month at room temperature. SLA batteries will self-discharge at about 5% per month. Self-discharge does not harm any rechargeable battery types except SLA. If you let an SLA battery sit around disconnected for long periods, it may destroy itself. Charge those jump starters in your trunk at least once every six months! If you have SLA batteries sitting around that you’d like to test, charge them up and get in touch with me – I have a tester that can measure exactly how much power a battery can provide.


Many, many other web sites.