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Author Topic: power supply voltage for agms  (Read 5762 times)
WH6DIQ
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Posts: 9




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« on: January 12, 2013, 06:54:47 PM »

Aloha,

I have been using a powerwerx ss30-dv to supply my 897 D. Normally, the meter on the radio indicates 13.8 v when using this. I have now added a powergate pg-40s and a pair of agm batteries in parallel. Although I did change the jumper in the powergate for the agm setting, it looks like the power supply can not be adjusted to the optimum 14.2 - 14.8 v peak charging voltage.

Am I correct in assuming I need to get a different power supply, or will this not significantly affect the long term performance/life of the agms?

Mahalo,

wh6diq
Richard
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K1CJS
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Posts: 5884




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« Reply #1 on: January 13, 2013, 10:46:46 AM »

It shouldn't affect the batteries too much.  If you're worried about it, simply get a charger that will supply the voltage you want to the AGMs, disconnect them from the powergate and give them a refresher charge every three months or so.  Yes, the extra voltage that may be on the batteries will go down the first time that you use your setup after that refresher charge, but the batteries should be OK in the meantime.  If you do go to battery power to exercise the batteries (I'm a firm believer that that should be done every three months also) disconnect and recharge them right afterwards.
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WH6DIQ
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Posts: 9




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« Reply #2 on: January 14, 2013, 08:27:55 AM »

I was really hoping for more definitive, technical info...thanks anyway.

73

wh6diq

Richard
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AA4PB
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Posts: 12686




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« Reply #3 on: January 14, 2013, 10:22:33 AM »

I expect that with a power supply limited to 13.8VDC output, the PowerGate charger will never be able to apply the bulk charge rate. The battery should eventually reach full charge, but it will take much longer.

Switching power supplys are often not adjustable or the mfgs don't provide schematics or adjustment instructions. Linear supplies are usually easier to work with when it comes to making adjustments to the output voltage.
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W8JX
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Posts: 5476




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« Reply #4 on: January 14, 2013, 12:09:08 PM »

Aloha,

I have been using a powerwerx ss30-dv to supply my 897 D. Normally, the meter on the radio indicates 13.8 v when using this. I have now added a powergate pg-40s and a pair of agm batteries in parallel. Although I did change the jumper in the powergate for the agm setting, it looks like the power supply can not be adjusted to the optimum 14.2 - 14.8 v peak charging voltage.

Am I correct in assuming I need to get a different power supply, or will this not significantly affect the long term performance/life of the agms?

Mahalo,

wh6diq
Richard

The only thing you are loosing here is the ability to rapid charge batteries. Unless a rapid recharge is desired there is little cause for concern.
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WH6DIQ
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Posts: 9




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« Reply #5 on: January 14, 2013, 08:06:27 PM »

OK, thanks. I did note that the indicator on the powergate did seem to cycle properly over a period of time through the peak charge indicator, and then the float indicator (where it remains). The batteries were pretty well fully charged when I first connected them, of course.

I plan on cutting off the grid power in the next week or two, and seeing how long I can actually continue to operate before voltage drops to about 11.8, then monitor the charging cycle again when back on grid. 

73

wh6diq
Richard
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W8JX
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« Reply #6 on: January 15, 2013, 06:04:26 AM »


I plan on cutting off the grid power in the next week or two, and seeing how long I can actually continue to operate before voltage drops to about 11.8, then monitor the charging cycle again when back on grid. 


I would suggest a lower cutoff as you will not get much capacity. Even 11.5 would yield about 10% more run time before recharge.
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WH6DIQ
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Posts: 9




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« Reply #7 on: January 15, 2013, 08:58:56 AM »

On review of the specs and info that were included with the batteries, 11.8 is taking it down to about 18%, 11.5 is 100% discharged. They also state that a 14.1 to 14.7 volts are needed for the deep cycle charging.

Obviously, I want to get the maximum life from the batteries under my expected usage (3 - 10 years per the maker in "standby" use). I just want to try and understand the "why" of the recommendations, to make a good decision on the equipment I will be using long term. It seems the manufacturers (of the batteries and the other equipment) provide just enough info to confuse non-engineers!

To add to my confusion, the powerwerx info on the power supply indicate it is adjustable (via internal pot) to 14.1 output...but I have yet to confirm this, as other info also from the company states it is not adjustable, and I don't really want to take apart the unit without being sure.

Mahalo for your input...

wh6diq
Richard
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W8JX
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Posts: 5476




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« Reply #8 on: January 15, 2013, 10:39:46 AM »

On review of the specs and info that were included with the batteries, 11.8 is taking it down to about 18%, 11.5 is 100% discharged. They also state that a 14.1 to 14.7 volts are needed for the deep cycle charging.

I suspect these are no load static voltages not under load. Again on charge voltage, a higher voltage will charge quicker.
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LA9XSA
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« Reply #9 on: January 18, 2013, 12:34:46 AM »

On review of the specs and info that were included with the batteries, 11.8 is taking it down to about 18%, 11.5 is 100% discharged.
Note that the manufacturer's voltage numbers are open voltage measured at the battery terminals. When the radio's LCD shows the battery voltage, it also shows the voltage drop over the diode in the Super Powergate, fuses, and cables. Get out a multimeter and masure the battery voltage - I think you'll find that when the radio shows 11.5 volts, the actual battery voltage is 11.8 or 11.9 or something like that.

I have a self-built trickle charge diode and resistor that I connect to a netbook power supply to charge my 7Ah AGM and run my radio. I set the PSU to 14 volts most of the time, which gives about 13.5 or 13.6 volts to the battery when floating, but I sometimes set the PSU to 15 volts for conditioning the battery with 14.5 volts.
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WH6DIQ
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Posts: 9




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« Reply #10 on: January 19, 2013, 10:24:53 AM »

Aloha, and thanks for the responses to all.

I guess the one question I still have is this: What affect does the rate of charge (during peak charge) have on the life of the battery? If I understand correctly, the manufacturer is specifying the 14.1 -14.7 voltage, but consensus here seems to be that the 13.8 will still charge the battery, just taking a longer time to do so (which is not a factor to me). I can switch to a different power supply easily enough, but I want to get the maximum life from these batteries. I want to understand why, however.

73

wh6diq
Richard
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AA4PB
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Posts: 12686




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« Reply #11 on: January 19, 2013, 05:18:16 PM »

The batteries "float charge" at 13.8V. That is, at 13.8V they will draw whatever current they need from the supply to keep them topped off. The supply needs to be higher than the battery voltage (usually 14+) in order to get the battery to continue drawing a significant amount of current (thus charging) after it has reached 13.8V. If the supply is only 13.8V then the battery current will taper off after the battery reaches 13.8V (close to a full charge) and it will thus take much longer to get the final few per-cent of remaining charge.

Charging at 13.8 won't damage the battery. In fact, it is probably easier on the battery than taking it higher to get a faster charge. The two things that will shorten the lifetime of a battery is overcharging (i.e. leaving it at 14+ volts after it has reached a full charge) and deep discharge (i.e. continuing to discharge after the voltage has reached about 10V).
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K1CJS
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« Reply #12 on: February 22, 2013, 04:54:04 AM »

...I guess the one question I still have is this: What affect does the rate of charge (during peak charge) have on the life of the battery? If I understand correctly, the manufacturer is specifying the 14.1 -14.7 voltage, but consensus here seems to be that the 13.8 will still charge the battery, just taking a longer time to do so (which is not a factor to me). I can switch to a different power supply easily enough, but I want to get the maximum life from these batteries. I want to understand why, however.

Here's a way that may be more understandable.  In effect, the more you force a charge into a battery quickly, the warmer the battery may get.  The warmer the battery gets, the more the electrolyte may have the opportunity to "boil away," and the shorter the life of the battery will be.  If the battery is charged at 13.8 volts, it will not be forced to take more of a charge--which may happen at the 14.2 rate--it will not get 'warm' enough to evaporate the electrolyte, and may well last longer because of it.
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AA4HA
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Posts: 1378




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« Reply #13 on: February 24, 2013, 01:43:42 PM »

Direct quotes from Optima batteries;

Trickle Charging:
"Yes, and you can use any charger on an OPTIMA Battery as long as the voltage is regulated properly. If your charger will remain on indefinitely, the voltage should be at 13.8 volts maximum with a one-amp maximum current."

Regular Charging:
"For regular charging we recommend a maximum of 10-amps, 13.8-15.0 volts. For float charging, we recommend 1 amp maximum, 13.2-13.8 volts."

http://www.optimabatteries.com/us/en/support/faqs/

I use two 8050-160 D31T Yellowtop Batteries in parallel for 150A/Hr (C/20) capacity to run my station. It is important that if you use batteries in parallel that they be of the same vintage and ideally from the same manufacturing batch to minimize self-discharge. I charge and discharge them through 1N6098 Schottky diodes (50A) with fusing so they are isolated from each other.
« Last Edit: February 24, 2013, 01:55:17 PM by AA4HA » Logged

Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
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