have i killed my batteries?

[cuthound]

My twopenneth' s worth.

 

By charging AGM batteries at 17 volts are likely to have shortened their lives, because AGMs are a type of valve regulated sealed lead acid battery and you will have "vented" some of the electrolyte to atmosphere. In the short term they will behave normally.

 

When undertaking a controlled discharge to assess battery capacity, you need a variable load, so that you can compensate for the falling battery voltage, which if unchecked will cause the current to drop along with the voltage as the battery discharges. Don't forget you are trying to assess the amp hours that the battery now contains.

 

So to answer the OP's question, I think he has wounded, rather than killed his batteries.

 

Edited to add the last sentence.

Edited December 15, 2015 by cuthound

[Graham.m]

My twopenneth' s worth.

 

By charging AGM batteries at 17 volts are likely to have shortened their lives, because AGMs are a type of valve regulated sealed lead acid battery and you will have "vented" some of the electrolyte to atmosphere. In the short term they will behave normally.

 

When undertaking a controlled discharge to assess battery capacity, you need a variable load, so that you can compensate for the falling battery voltage, which if unchecked will cause the current to drop along with the voltage as the battery discharges. Don't forget you are trying to assess the amp hours that the battery now contains.

 

Your two penneth is good. Personally I would use a current monitor to assess amp hours out. Adjusting loads when they are hot is not the easiest of jobs and accurate setting can be difficult. The variation tends to be minor and within a few percent.

 

The days of easily being able to source the big DC rheostats have unfortunately gone

[Graham.m]

No it wasn't.

 

Won't you ever stop?

 

How much practical experience have you got doing battery load testing?

[nicknorman]

When was the last time you did a controlled load test on a battery. No I am not talking about putting 200A on a battery to boil the kettle. A real heavy duty battery load test? Probably never

 

Routinely when I conduct maintenance on aircraft. They have to have an annual battery capacity check.

I have blocked you

 

You are indeed merciful after all.

My twopenneth' s worth.

By charging AGM batteries at 17 volts are likely to have shortened their lives, because AGMs are a type of valve regulated sealed lead acid battery and you will have "vented" some of the electrolyte to atmosphere. In the short term they will behave normally.

When undertaking a controlled discharge to assess battery capacity, you need a variable load, so that you can compensate for the falling battery voltage, which if unchecked will cause the current to drop along with the voltage as the battery discharges. Don't forget you are trying to assess the amp hours that the battery now contains.

So to answer the OP's question, I think he has wounded, rather than killed his batteries.

Edited to add the last sentence.

It's all a bit faffy though, to keep having to adjust the load etc. We use an automatic capacity checker that drains the battery at constant current (which you can set) whilst counting time. At the preset minimum voltage (10.5v I think) the timer stops and it automatically flips to recharging the battery. Unfortunately last time I used it it wasn't working properly and ever since I keep meaning to build a new one. Edited December 15, 2015 by nicknorman

[WotEver]

 

How much practical experience have you got doing battery load testing?

The last time I tested a bunch of batteries for a client (about 18 months ago) I didn't want to guess at it because some of these were for critical applications. I used the Alfabat Pro. I don't own one but was able to borrow one for a couple of weeks. At that time I tested around 40 batteries and printed out the graphs for each one for the owner's records.

 

Why, how much practical experience do you have?

 

If you think that a 10A load would immediately pull a 500Ah battery down by 0.7V I'd suspect not much.

 

Tony

Routinely when I conduct maintenance on aircraft. They have to have an annual battery capacity check.<snip> We use an automatic capacity checker that drains the battery at constant current (which you can set) whilst counting time.

Sounds like the Alfabat? Edited December 15, 2015 by WotEver

[Graham.m]

The last time I tested a bunch of batteries for a client (about 18 months ago) I didn't want to guess at it because some of these were for critical applications. I used the Alfabat Pro. I don't own one but was able to borrow one for a couple of weeks. At that time I tested around 40 batteries and printed out the graphs for each one for the owner's records.

 

Why, how much practical experience do you have?

 

If you think that a 10A load would immediately pull a 500Ah battery down by 0.7V I'd suspect not much.

 

Tony

Sounds like the Alfabat?

 

I take it you use the 30, put it on the box and read the results.

 

Suspect you have not done it the hard way.

 

I take it that not much happening in post production then

Why don't you go and get the OPs battery and run it for him

[nicknorman]

Sounds like the Alfabat?

No it's home made (not by me) in a wooden box with a few 2N3055 transistors on a big heat sink for the constant current, an electromechanical hour meter and a battery charger on top! Inside is some veroboard with some ancient looking circuitry and lots of dodgy wiring. Hence I'm thinking of making a new one.

[Graham.m]

nicknorman, on 15 Dec 2015 - 4:23 PM, said:

Routinely when I conduct maintenance on aircraft. They have to have an annual battery capacity check.<snip> We use an automatic capacity checker that drains the battery at constant current (which you can set) whilst counting time.

 

Ah so now your a qualified aircraft mech, Interesting you did not mention that in your long list of qualifications posted recently

[nicknorman]

nicknorman, on 15 Dec 2015 - 4:23 PM, said:

 

 

Ah so now your a qualified aircraft mech, Interesting you did not mention that in your long list of qualifications posted recently

That "ignore" isn't last very long! I am a qualified glider and motorgliders mech. For the tug I do the work and someone else signs it off. Edited December 15, 2015 by nicknorman

[WotEver]

I take it you use the 30, put it on the box and read the results.

No, the Pro, like I said in my post.

 

Suspect you have not done it the hard way.

Not for years, no. I used to though.

 

I take it that not much happening in post production then

Not that it's any of your business but I did 70 hours last week - how much did you do?

No it's home made (not by me) in a wooden box with a few 2N3055 transistors on a big heat sink for the constant current, an electromechanical hour meter and a battery charger on top! Inside is some veroboard with some ancient looking circuitry and lots of dodgy wiring. Hence I'm thinking of making a new one.

Ooh, the last time I played with 2N3055s I was working with a guy trying to coax a 741 into driving one to control the heater motor speed on a Rover 75!

Edited December 15, 2015 by WotEver

[nicknorman]

 

I take it that not much happening in post production then

 

Not that it's any of your business but I did 70 hours last week - how much did you do?

Blimey that it a lot of time spent producing posts, you should type faster!

[WotEver]

Lol!!

[Graham.m]

Not that it's any of your business but I did 70 hours last week - how much did you do?

 

 

Don't have to, but I do the odd bit when I feel like it.

 

In the old days I would have asked if you got your training at Auntie, but I doubt, so many place today for media training

[WotEver]

I have worked for the Beeb and ITV. We do work for every terrestrial channel plus some of the digital stations including Sky. Plus film and below the line. In the last two weeks we have made 41 TV commercials for clients as diverse as Drayton Manor Park to Peugeot.

[emlclcy]

I have 4 off these batteries, 2 are on the boat two are in my shed. I'm trying to see if I can mount the other two on the boat also to replace the 110ah batteries but the size of the 250's is a little restrictive.

Last night I briefly switched on the psu and the battery held the current limit (4A) at 13.5 ish volts so maybe they have recovered after a little 'boost'! (borrowing a fluke 77 to measure them tonight)

I've just ebayed a 100A current shunt so I can monitor the current. I thought of using a 500watt inverter I have running some light bulbs as a load, this should be a constant load to the batteries, as the battery voltage drops the current will increase and with the shunt I can log what happens.

with say a 200watt load, how low a voltage would you take the battery?

[nicknorman]

I have 4 off these batteries, 2 are on the boat two are in my shed. I'm trying to see if I can mount the other two on the boat also to replace the 110ah batteries but the size of the 250's is a little restrictive.

Last night I briefly switched on the psu and the battery held the current limit (4A) at 13.5 ish volts so maybe they have recovered after a little 'boost'! (borrowing a fluke 77 to measure them tonight)

I've just ebayed a 100A current shunt so I can monitor the current. I thought of using a 500watt inverter I have running some light bulbs as a load, this should be a constant load to the batteries, as the battery voltage drops the current will increase and with the shunt I can log what happens.

with say a 200watt load, how low a voltage would you take the battery?

Yes the inverter is constant power but not constant current, so whereas with a resistor the current would go down over time, with an inverter the current will go up over time, but as you say you can check it every now and again.

 

Do we presume 1 250AH battery under test, or two in parallel? 200w from the inverter will be perhaps a bit under 20A or just under C10 which is not too bad. I'd certainly take them no lower than 12v but on the other hand you probably don't need to go that low. Having discharged them to perhaps 12.3v you can let them rest and then measure the voltage to get a pretty good idea of SoC, and from the amount of AH you have taken out to get to the SoC you can work out the actual capacity.

 

If they have never been used before the capacity might increase a bit after a few cycles.

Edited December 15, 2015 by nicknorman

[WotEver]

I wouldn't take it below 50%.

 

200W @ 12V would be around a 16A load which equates to only around C3 so an indicated 11.8V on load would be as low as I'd want to go.

 

Unless I've got my maths wrong anyone?

 

I've assumed 500Ah

Further to Nick's post I agree - why go all the way down? After a few hours you'll have enough info for a close approximation.

[cuthound]

Your two penneth is good. Personally I would use a current monitor to assess amp hours out. Adjusting loads when they are hot is not the easiest of jobs and accurate setting can be difficult. The variation tends to be minor and within a few percent.

 

The days of easily being able to source the big DC rheostats have unfortunately gone

I would hope so, 18 months ago I retired from a 41 year career in critical closer and cooling.

 

In that time I covered everything, maintenance, commissioning, technical support, design and project management, ending up at senior manager level (department head).

 

However I am still learning about the way batteries behave in a marine environment, hence my limited number of posts on boating electrical practicalities.

 

You don't need to use DC rheostats to test boat batteries in situ. The boat has plenty of DC load on it, which can be utilised to good effect (fridge, lights etc).

[Graham.m]

I would hope so, 18 months ago I retired from a 41 year career in critical closer and cooling.

 

In that time I covered everything, maintenance, commissioning, technical support, design and project management, ending up at senior manager level (department head).

 

However I am still learning about the way batteries behave in a marine environment, hence my limited number of posts on boating electrical practicalities.

 

You don't need to use DC rheostats to test boat batteries in situ. The boat has plenty of DC load on it, which can be utilised to good effect (fridge, lights etc).

Trouble with using the items on the boat is they are not as constant as a resistor, fridge runs for few minutes then off and so on. Edited December 15, 2015 by Graham.m

[emlclcy]

battery voltage update, as of tonight one measures 13.20v, the other 13.12v

just wait for the shunt to turn up now and will report back

[Nickhlx]

Sounds good, at least for the time being !

[WotEver]

Yeah, they sound just fine so far.

[Graham.m]

battery voltage update, as of tonight one measures 13.20v, the other 13.12v

just wait for the shunt to turn up now and will report back

Sounds very good fingers crossed

[Loafer]

That "ignore" isn't last very long! I am a qualified glider and motorgliders mech. For the tug I do the work and someone else signs it off.

 

Not to mention his ATPL(H).

[cuthound]

Trouble with using the items on the boat is they are not as constant as a resistor, fridge runs for few minutes then off and so on.

True, when I bought DQ I used the 20 odd halogen lamps to control the discharge rate, adjusting the current by turning more on, and checking every 15 minutes.

 

As I convert to LEDs I have kept the cold halogens to use as a load bank again if needed.