Batteries for Dodd power amps

HAL · « **on:** 11 Nov 2009, 02:33 pm »

Just thought it might be interesting to discuss big batteries for the Dodd battery powered amps as folks get them.

I have three Optima Blue Top D31M 75 amp-hour batteries for the setup when my amp arrives for the Super-V's. I have had these for a few years and they are partly sulfated, so recharging them now. These were originally for backup power during storms, but now being put to use for audio!

These are Absorbed Glass Mat (AGM) batteries designed for deep discharge operation. Internal resistance at full charge is 0.0025 ohms!

Just got a BatteryMINDer charger that has de-sulfation capability. It is supposed to be able to recover batteries that are not overly sulfated to mostly full charge capability. Also got the temperature probe to charge the batteries correctly for the ambient temperature/battery temperature. Cost about $128 for the setup.

The instructions say that a battery depending on state may take up to two weeks to recover to it's final charge state. Should have battery number 1 done by the time my Dodd PA arrives!

My plan is to connect all three batteries in parallel to increase on time and lower resistance even further. Makes them easy to recharge once they are all up to full capability.

Any other ideas out there?

R_burke · « **Reply #1 on:** 11 Nov 2009, 03:34 pm »

I'd love to see some pictures of peoples set up with batteries. I'm having a hard time imagining how the whole thing would look.

gprro · « **Reply #2 on:** 12 Nov 2009, 03:22 am »

Hal,

Sounds like you've done a little battery research. Something I was going to start doing. I have some 105 Ah minkota trolling batteries. Almost never used. Problem is I just looked at the build date and it's Feb 02. I have the minkota charger somewhere also. You think my batteries are still good?

If I go the battery rout, which I think I would like to do. I could see building a nice wood enclosure for them. Similar to the Dodd amp cosmetics.

HAL · « **Reply #3 on:** 12 Nov 2009, 04:55 am »

gprro,
Are they flooded cell or AGM style batteries? Have they been kept on charge when not in use?

From what I am reading, the flooded cells do not last as long as the AGM style. The AGM's are supposed to have about a 10 year life if maintained properly.

I was only charging my 75A-H and 100A-H AGM's every 6 months over the last two years as recommended. When I checked the 75A-H cells they were at the 25% capacity point. That is why I am doing the de-sulfation process. Will probably end up buying a second BatteryMINDer to have one on the 75A-H cells and the other on the 100A-H cells all the time to keep them in shape.

satfrat · « **Reply #4 on:** 12 Nov 2009, 07:34 am »

Quote from: HAL on 11 Nov 2009, 02:33 pm

Just thought it might be interesting to discuss big batteries for the Dodd battery powered amps as folks get them.

I have three Optima Blue Top D31M 75 amp-hour batteries for the setup when my amp arrives for the Super-V's. I have had these for a few years and they are partly sulfated, so recharging them now. These were originally for backup power during storms, but now being put to use for audio! These are Absorbed Glass Mat (AGM) batteries designed for deep discharge operation. Internal resistance at full charge is 0.0025 ohms!

Just got a BatteryMINDer charger that has de-sulfation capability. It is supposed to be able to recover batteries that are not overly sulfated to mostly full charge capability. Also got the temperature probe to charge the batteries correctly for the ambient temperature/battery temperature. Cost about $128 for the setup.

The instructions say that a battery depending on state may take up to two weeks to recover to it's final charge state. Should have battery number 1 done by the time my Dodd PA arrives!

My plan is to connect all three bateries in parallel to increase on time and lower resistance even further. Makes them easy to recharge once they are all up to full capability.

Any other ideas out there?

At first read of your thread, the question that popped into my head was if you are planning on using all 3 batteries in parallel, how will you be recharging them? Can you recharge all 3 in parallel together and if so, how long to you suspect it'll take to get them back to peak power? Surely less than 2 weeks.

It sounds like you have it all planned out, good luck and happy listening with them Dodd amps.

Cheers,
Robin

HAL · « **Reply #5 on:** 12 Nov 2009, 12:25 pm »

Yes, my plan is to have all three batteries in parallel for use.

The de-sulfation process may take up to two weeks to recover full charge capability in the battery. Normal recharging takes hours depending on discharge level. The charger will work at an 8 amp rate, so just depends on how many hours the batteries were used.

The internal impedance of the setup with three batteries in parallel is 0.00083 ohms! Short term current capability of 3375amps. Not to shabby for an audio power supply.

EDIT: Spotted Gary's thread about the new battery PA's. Continuous current draw is 5 amps, so should get 40+ hours out of the three Optima's in parallel before recharge. That is one serious listening session!

HAL · « **Reply #6 on:** 12 Nov 2009, 12:29 pm »

Quote from: gprro on 12 Nov 2009, 03:22 am

Hal,

Sounds like you've done a little battery research. Something I was going to start doing. I have some 105 Ah minkota trolling batteries. Almost never used. Problem is I just looked at the build date and it's Feb 02. I have the minkota charger somewhere also. You think my batteries are still good?

If I go the battery rout, which I think I would like to do. I could see building a nice wood enclosure for them. Similar to the Dodd amp cosmetics.

gprro,
One other thing, if the batteries are flooded cell types, would not be good to use them indoors. They will vent hydrogen while charging and have sulfer dioxide fumes that are corrosive. The AGM and SLA style batteries are fine to use inside as they are sealed.

I did not find much online for the batteries you listed for some reason.

gprro · « **Reply #7 on:** 13 Nov 2009, 06:47 am »

They're Minn Kota MK20's. Looking at the top, there are two panels that open. One of which has warnings for sulfuric acid, and explosive gasses,

. Probably not a good idea for indoors,

. Should have realized that, haha. They're probably dead or compromised any way.

KS · « **Reply #8 on:** 15 Nov 2009, 05:45 am »

Hal

The desulfation effect might be lessened by connecting the batteries together. I'd use one battery at a time connected to the charger/desulfator until each battery is desulfated as much as possible. I use a Battery Minder trickle charger for the motorcycle and lawnmower batteries, and it seems to keep them strong longer than I'd expect. (I've seen debate on whether desulfation is real or urban legend. I've seen comments that the desulfators remove soft sulfate and can't touch hard sulfate. I don't know, but they seem to work for me.)

HAL · « **Reply #9 on:** 15 Nov 2009, 01:21 pm »

KS,
I am de-sulfating/charging the batteries one at a time. Will only put them in parallel for use with the Dodd amp once they are all up to full charge.

Will try the unit on the three in parallel for maintenance charging and see what happens. This version has an 8 amp charge mode, so maybe able to maintain them.

KS · « **Reply #10 on:** 17 Nov 2009, 09:48 pm »

Parallel operation, especially with a light load, can allow one or two batteries to loaf; there are no perfect connections and even the best have a slight voltage drop. If you number the batteries #1,2,3, consider connecting the output + to #1 battery and the output - to #3 battery. Connect the charge input + to #3 battery and the charge input - to #1 battery, or any other connection pattern to force the current flow across the most number of batteries and not just down the parallel wiring.

HAL · « **Reply #11 on:** 17 Nov 2009, 10:00 pm »

KS,
Will use that wiring setup.

Thanks!

HAL · « **Reply #12 on:** 21 Nov 2009, 07:08 pm »

After a week on the BatteryMinder the first Optima Blue Top went from 12.77VDC after charge to 12.93VDC after charge and 12 hour rest.

Battery number 2 is on charge now.

HAL · « **Reply #13 on:** 28 Nov 2009, 09:36 pm »

Battery #2 is fully charged and at the same level as battery #1.

The Dodd Battery PA should be shipping next week, so hope to have it for next weekend.

jtwrace · « **Reply #14 on:** 29 Nov 2009, 02:23 pm »

Do you know the Watt / to AH conversion? I have a Dodd Buffer on order and am wanting to know how many AH battery I should get. I first thought 35AH but don't really think that I need one that big. The Buffer is ~5 watts.

HAL · « **Reply #15 on:** 29 Nov 2009, 02:43 pm »

The Dodd Battery Buffer probably comes with two 12VDC SLA batteries. My Dodd Battery Preamp did.

Ok, here is some math for the morning.

Power = Volts X Amps.

Gary uses two 12VDC SLA batteries in the buffer from the pictures.

5 watts = 24 Volts x Amps.

5/24 = 0.208Amps

Now you have to decide how many hours you want to play before recharge.

For SLA or AGM batteries a C/20hour rate is very good.

So 0.208amps x 20 = 4.16 amp/hours.

This would be two 12VDC, 5amp-hour batteries just as Gary had in the unit at RMAF.

jtwrace · « **Reply #16 on:** 29 Nov 2009, 02:49 pm »

HAL

Thanks. Buffer does NOT come with any battery. Hmm. How many AH to get....

HAL · « **Reply #17 on:** 29 Nov 2009, 03:20 pm »

Looks like the buffer runs off 12VDC instead of 24VDC. Double the A-H capacity that I calculated.

So a 12VDC @ 10A-H SLA or AGM battery will give 20 hours of operation with the buffer.

jtwrace · « **Reply #18 on:** 30 Nov 2009, 04:29 pm »

Quote from: HAL on 29 Nov 2009, 03:20 pm

So a 12VDC @ 10A-H SLA or AGM battery will give 20 hours of operation with the buffer.

Hmm. That would be to good to be true.

20 AH battery it ia then. Perfect!

Danny Richie · « **Reply #19 on:** 30 Nov 2009, 05:02 pm »

I am running my buffer and the amp off of this pair of batteries.

I can run it all day long and it never drops below about 12.4 volts.