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Old 08-25-2012, 10:22 PM
medicineball medicineball is offline
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Default Transmitting while charging?

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Ok, it's time to look clueless - I throw myself on the mercy of the forum.

I'm running a 55 w 2-meter Yaesu rig off a deep cycle marine battery. I trickle charge the battery. I chose to do this instead of an AC-to-dc power supply because this system works when the AC power goes out.

Here's my question: is it bad for the charger in any way if it is hooked to the battery while I'm transmitting? What is happening to the charger current if I'm transmitting?

Old 08-25-2012, 10:38 PM
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Charger current goes to its maximum, and then returns to what is required by the state of the Battery system when you let go of the PTT. So, no Harm.
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Old 08-25-2012, 10:39 PM
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Buy you a solar trickle charger... they are dependable.
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Old 08-25-2012, 11:52 PM
technoprepper technoprepper is offline
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The situation is not as simple as some posters have suggested.

A wimpy charger with inadequate current limiting may burn up. This may also happen when connected to a heavily discharged battery.

A wimpy charger with current limiting lets the battery do most, but not all, of the work powering the radio during transmit. Since this involves pumping charge into and out of the battery, you are consuming your battery shelf life when transmitting. Crude approximation, a battery has a fixed life of X number of amp hours into and out of the battery. In reality, the rate that you pump that current into and out of the battery and how deep you discharge change the rate the battery is consumed at. With this type of charging setup, if power goes out at the end of a busy night of transmitting, your battery may be half discharged. Ironically, in this configuration, you might find that in some situations you run out of power during prolonged heavy operating even when the AC grid is working. A "trickle" only charger is a particularly bad example of this configuration. Some transceivers may use more power than a trickle charger provides even on receive.

A beefy charger with current limiting could power the radio and possibly keep charging the battery (if needed). If the current limit, adequate to run the radio, is higher than the healthy charge rate on the battery, it may overcharge the battery.

Multimode chargers can get confused about what mode they should be in when you draw power from a battery under load.

Some chargers were never really meant to be connected to a battery continuously for long periods of time, let alone one with a load and either the charger or battery, or both will be damaged.

You can connect the battery, output of a 13.8V regulated station power supply, and the transciever inputs together. Put a diode in series with the power supply to keep battery power from discharging through the supply (and possibly damaging the voltage regulator). This will effectively act as a constant voltage charger for the battery. It is not ideal for the life of the battery. Output voltage should be adjusted so the voltage on the other side of the battery is correct for constant voltage charging of your battery.

Equipment which properly handles this kind of operation is few and far between. For light duty use and at the expense of some battery life, you may get away with an improperly designed system. If you need to optimize battery life, plan on heavy operation, or are running a repeater then you should have a better system.

Another issue is that RF interference or audio frequency noise from the battery charger may leak into the radio or ground system and be transmitted.

Lack of a low voltage disconnect and your transceiver left on may deep discharge a battery, damaging it.

Note that having a radio connected to the output of a charger may result in damage to the radio if the battery is disconnected.

Here is one product you might want to investigate.
Power for the radio always comes from power supply except during a power outage or brownout. In addition, it includes a battery charger which will charge the battery from the power supply. Use with a 13.8V station power supply whose output voltage has been adjusted upward slightly. It is not ideal but an improvement over crude setups.

Some solar chargers may handle this kind of situation better, but not all. Some may additionally do maximum power point tracking when connected to a solar panel which is necessary to get the advertised rating of your solar panel on full sun. Solar power should be seriously considered for station power supply (see my previous posts on solar).

You can run the radio off a station power supply and have a separate (good) charger for charging the battery and manually switch to battery operation when power goes out. No good for a unattended repeater site and a bit of a nuisance when power is fluctuating on and off but minimal station engineering is required.

Don't forget to use the minimum transmit power that will get the job done.

For those who are not familiar, you should probably also be using ARES/RACES standard 15/30/45 amp powerpole connectors for your 12V radio gear. The three different ratings are interchangeable, they are just designed to crimp different wire sizes.
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Old 08-26-2012, 07:29 AM
Tevin Tevin is offline
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I agree with technoprepper's excellent insight and will add:

A battery charger and a power supply are not the same thing. Chargers in general, and automotive chargers in particular, should not be used as power supplies.

Power supplies can be used as chargers with the caveat that you will have to judge for yourself when the battery is fully charged. Otherwise, you can overcharge and cook your battery.

As for charging a battery while also using it...thats a dicey proposition. As technoprepper described, you risk ending up with less of a battery than you started with. I say avoid it unless your radio has charge/power functionality (most handheld radios can do this), or you are absolutely sure your power supply has enough current capacity to push the radio and the battery at the same time. Even then, you will need to disconnect the battery at some point to avoid overcharge.

To answer the original question, using a 55 watt radio while connected to a battery and a small trickle charger is probably ok as long as the charger has built-in current limiting. Most of the cheapie chargers do not. The worst that can happen is you fry the charger.

In my experience, home made charge/power setups are usually more trouble than they are worth. It's easier/safer to have chargers for the batteries and power supplies for the radios and that's that. There is very little benefit to mixing them.

The one exception is solar chargers. With a solar panel and an appropriate charge controller, it is ok if the battery runs the radio and charges at the same time. You still need to pace your radio use so you are not draining the battery faster than the solar can fill it. A basic 10 amp charge controller is about fifty bucks. MPPT controllers are better; they start at $250 & go up from there. I don't want to turn this into a solar discussion but if you go back and look at some of my old postings, I get into solar power in great detail.

Good luck with your project; hope I've been helpful...
Old 08-26-2012, 09:08 AM
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Many thanks for the responses!
Old 08-26-2012, 08:05 PM
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There are batteries and systems designed just for this kind of operation, but they aren't something you're just going to pick up off the shelf. I have a system in my shack that was originally designed to keep communications sites on line. It basically keeps the battery on float charge and when power fails to the AC supply it automatically and near instantly switches to battery power. These kinds of systems are commonly used at repeater sites, cell towers, server farms and much more. These systems are typically designed around their intended load and use, so there is a fair amount of math that goes into the system planning.

There are a couple of products available that are targeted at ham radio users to charge batteries from the power supply and automatically switch to battery on AC failure. Here is a link to a charger designed for use while the battery is connected to a load.

Also, be prepared to spend big bucks on batteries designed for this kind of use. I use a Marathon M12V90F to power a few of my 12vdc radios and a lamp in the shack while charging the battery with a charger designed for this kind of use.
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