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Trojan Battery Replacement


davidb

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In our boat we had 4 Trojan T-6220 batteries, and two have expired. It is running satisfactorily on the remaining two, so is it bad practice to fit just two new ones and see how they go? I think these are the replacements https://www.tayna.co.uk/leisure-batteries/trojan/t-105/

 

Also, in the specifcations, they list the followng AH ratings, so do I work on the c20 value?

Capacity (C5)

 
Capacity (C10)  
Capacity (C20)  
Capacity (C100)  
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First question:   Yes.  The two new batteries will have a much greater actual  capacity than the old ones.  This means chargers may shut off when the old ones are full and the new ones are not, leading to sulphation of the new ones.

 

Second Q.  It depends what you are doing with the batteries and in what time you expect them to be discharged.  Driving a fork lift or a golf buggy you would expect to mostly discharge a battery in a half shift/ round of golf taking 3 or 4 hours so use C5.  In a boat you do not usually discharge so fast, so C10 or C20 are achievable.

C100 would be for something like a  phone exchange back up with a low load for a long time.

N

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Yes, use the C20 rating because that is what most lesser battery suppliers use but some sharp boys may well quote the 5 hour rate to make their product look better so take care.

 

The reason for not fitting a whole set is because if one battery in a parallel string develops internal shorts (as an old one is likely to)  it will discharge all the parallel batteries allowing the new ones to sulfate and suffer deeper cycling. If you can keep up very regular battery monitoring so you  quickly pick up a shorting battery then at your own risk you could mix old and new batteries in the bank.

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47 minutes ago, BEngo said:

First question:   Yes.  The two new batteries will have a much greater actual  capacity than the old ones.  This means chargers may shut off when the old ones are full and the new ones are not, leading to sulphation of the new ones.

 

 

I don't think that is totally correct. They will have a smaller capacity and will charge faster but as they reach a higher state of charge than the new ones their terminal voltage will rise higher than the new ones so proportionally more charge will flow into the new set. I think the difference in the state of charge when the charge source shuts down will be minimal.

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45 minutes ago, Tony Brooks said:

 

I don't think that is totally correct. They will have a smaller capacity and will charge faster but as they reach a higher state of charge than the new ones their terminal voltage will rise higher than the new ones so proportionally more charge will flow into the new set. I think the difference in the state of charge when the charge source shuts down will be minimal.

 

I think so too.

 

More specifically, as four batts are in parallel their terminal voltages are by definition all the same, all the time. 

 

So during charging the highest capacity battery will hold the terminal voltage of all four down while it sucks in most of the output from the charger, and the whole bank SoC will rise in step with the SoC of the highest capacity battery.

 

 

Edited by MtB
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1 hour ago, Tony Brooks said:

 

I don't think that is totally correct. They will have a smaller capacity and will charge faster but as they reach a higher state of charge than the new ones their terminal voltage will rise higher than the new ones so proportionally more charge will flow into the new set. I think the difference in the state of charge when the charge source shuts down will be minimal.

Also agree.

Perhaps a better solution would be to measure the capacity of the remaining two. If they are pretty good (as the OP suspects they are) then keeping them seems like a plan.

If they are poor then save work and replace all together.

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37 minutes ago, Floating Male said:

If they are pretty good (as the OP suspects they are) then keeping them seems like a plan.

 

Only providing he keeps a close eye on them so they can't discharge the two new batteries. I am not sure it is practical to test the capacity unless he can fully charge them, discharge over a period and use rested voltage to get state of charge and then Ah used from a monitor to assess the remaining capacity.  I certainly don't think it is practical to fully charge them and then discharge with a known current for hours on end unless you have them at home.

1 hour ago, MtB said:

 

I think so too.

 

More specifically, as four batts are in parallel their terminal voltages are by definition all the same, all the time. 

 

So during charging the highest capacity battery will hold the terminal voltage of all four down while it sucks in most of the output from the charger, and the whole bank SoC will rise in step with the SoC of the highest capacity battery.

 

 

 

Really not nit picking and , as expected, I agree, but I am sure the OP has 2 pairs of series batteries wired in parallel to give 12V form 4 x 6V batteries.

 

The result will be the same as each series pair will act as one 12V battery, the OP increases the risk of damging his new series pair.

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5 minutes ago, Tony Brooks said:

 

Only providing he keeps a close eye on them so they can't discharge the two new batteries. I am not sure it is practical to test the capacity unless he can fully charge them, discharge over a period and use rested voltage to get state of charge and then Ah used from a monitor to assess the remaining capacity.  I certainly don't think it is practical to fully charge them and then discharge with a known current for hours on end unless you have them at home.

 

Really not nit picking and , as expected, I agree, but I am sure the OP has 2 pairs of series batteries wired in parallel to give 12V form 4 x 6V batteries.

 

The result will be the same as each series pair will act as one 12V battery, the OP increases the risk of damging his new series pair.

 

 

Good point. I had overlooked the fact that the OP is using 6v batts, so the are not all in parallel.

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The burning question is why 2 are better than the other pair. And how does this relate to the way they are connected?

Sounds as though the charging has not equalised possibly due to the way that they are connected?

Four new ones may go the same way.

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2 minutes ago, Tracy D'arth said:

The burning question is why 2 are better than the other pair. And how does this relate to the way they are connected?

Sounds as though the charging has not equalised possibly due to the way that they are connected?

Four new ones may go the same way.

 

Good point, lets have a photo or diagram.

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3 minutes ago, Tracy D'arth said:

The burning question is why 2 are better than the other pair. And how does this relate to the way they are connected?

Sounds as though the charging has not equalised possibly due to the way that they are connected?

Four new ones may go the same way.

 

I remain to be convinced the interconnects are that important. Anyone shelling out for Trojans in the fist place is pretty likely to understand the importance of fat enough good quality interconnects already, in which case the exact pattern of connecting makes hardly any difference. It always strikes me as something people seize on instead of figuring out the real fault.

 

My bet is the boat ran for years on two Trojans, then a second pair were added and the originals have now had it.

 

 

 

Edited by MtB
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Thanks again for all the input. I have resigned myself to getting 4, but before fitting them, I shall do a test run for a few days with the remaining two, then take them home for maintenance and possible sale or use for something else. Last back end they wouldn't keep the fridge going properly overnight if we had any TV use, so we could see what the difference with two new ones on their own is before taking them out.

 

Each dud one was in a separate 12v pair ISTR

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1 hour ago, davidb said:

Thanks again for all the input. I have resigned myself to getting 4, but before fitting them, I shall do a test run for a few days with the remaining two, then take them home for maintenance and possible sale or use for something else. Last back end they wouldn't keep the fridge going properly overnight if we had any TV use, so we could see what the difference with two new ones on their own is before taking them out.

 

Each dud one was in a separate 12v pair ISTR

 

Presumably you are aware they like a nice strong desulphation charge at about 16.0V from time to time?

 

Even in normal charging the spec sheet specifies a finishing charge at 15.1V IIRC. Your duff pair might yet be recoverable if you haven't been doing this, but I am not an expert on Trojans.

 

 

Edited by MtB
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2 hours ago, davidb said:

Well they haven't gone to the scrapyard yet thanks for that info Mike,- I had never thought of that. 

 

 

You're welcome. Have a look at old threads using the search facility (top right of every page). There has been a LOT of discussion about desulphating Trojans here over the years.

 

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On 23/03/2022 at 08:37, BEngo said:

First question:   Yes.  The two new batteries will have a much greater actual  capacity than the old ones.  This means chargers may shut off when the old ones are full and the new ones are not, leading to sulphation of the new ones.

 

Second Q.  It depends what you are doing with the batteries and in what time you expect them to be discharged.  Driving a fork lift or a golf buggy you would expect to mostly discharge a battery in a half shift/ round of golf taking 3 or 4 hours so use C5.  In a boat you do not usually discharge so fast, so C10 or C20 are achievable.

C100 would be for something like a  phone exchange back up with a low load for a long time.

N

 

Telephone exchanges specify battery capacity at C10 and the batteries are dimensioned to provide the full load for 1 hour when they are at 80% of original (new) capacity.

 

For a boat I would use the C20 capacity.

Edited by cuthound
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  • 3 weeks later...

We have had a week on the boat with only the two old batteries and they have been fine for cruising every day. I did an overnight test with just the panel voltmeter (no measuring of amps, I'm afraid) and have attached my readings. Yesterday I removed them and fitted the 4 T-105s and will do another static test shortly. All connections are good and solid.

oldPair.jpg

4batts.jpg

negTerm.jpg

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If the readings shown are typical you are going to seriously compromise any new batteries as they will sulphate and lose capacity.

Ideally you should get the batteries back to 99.99% state of charge daily, but in reality every 2 or 3 days will reduce your sulphation effect.

 

You need to get them charged.

 

The battery is fully charged when it is reading 14.4-14.6 volts & with a current of under 2% (ideally 1%) of battery capacity (so if you have 200Ah of capacity the charger should be charging at under 4 amps) and has not changed (up or down) for at least one hour.

 

What battery voltage is showing during the '2nd day' ? Do you have solar panels ?

Edited by Alan de Enfield
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14 minutes ago, Alan de Enfield said:

The battery is fully charged when it is reading 14.4-14.6 volts & with a current of under 2% (ideally 1%) of battery capacity (so if you have 200Ah of capacity the charger should be charging at under 4 amps) and has not changed (up or down) for at least one hour.

 

That could be a bit confusing in that every time a load comes on a battery that is well charged but still being charged will jump up and stay up each time a load is applied to the batteries until the load is removed. So each time the fridge (for example) comes on the amps will jump up until the fridge turns off. Just be aware this effect could confuse until you recognize what is happening and allow for it.

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1 minute ago, Tony Brooks said:

 

That could be a bit confusing in that every time a load comes on a battery that is well charged but still being charged will jump up and stay up each time a load is applied to the batteries until the load is removed. So each time the fridge (for example) comes on the amps will jump up until the fridge turns off. Just be aware this effect could confuse until you recognize what is happening and allow for it.

 

Indeed - for clarity I should have added "with everything turned off" (except the battery charger)

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34 minutes ago, Alan de Enfield said:

 

Indeed - for clarity I should have added "with everything turned off" (except the battery charger)

 

Which on a liveaboard CCer, can approaching impossible to achieve because stuff WILL keep coming on here and there, and small background currents get drawn all over the place on a modern boat.

 

Everything to do with batteries is a compromise, so for the OP getting the tail current down to approaching 2% at all will be a good compromise, and a desulfation cycle every few months will compensate.

 

First step in running a desulfation cycle for the OP will be to fit a good quality ammeter. 

 

 

 

 

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is reading 14.4-14.6 volts & with a current of under 2% (ideally 1%) of battery capacity"

 

All the readings are with no charger just running the battery down to show how long it was lasting with the fridge thermostat working normally, and normal evening usage with no engine. Tomorrow I shall see what it gets up to with the engine running again. That will be when we leave Liverpool having had a week on shore power.

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On 23/03/2022 at 09:09, davidb said:

Are we all happy with Tanya as a supplier?

You've had some good advice above, but I've not seen this answered. So I'll chip in with I think it'll be a pretty strong Yes. I've seen many recommendations here which reflect my own experience (albeit of a few years ago now) which was great service, keen pricing and excellent quick delivery to wherever your boat is. I'd have no hesitation in using Tayna again.

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