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Old 21-06-2017, 15:45   #1
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Location: Knoxville Tn
Boat: Roberts Spray 33
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Is my Battery Charger Failing

I have a Newmar Phase 3 PT-25 battery charger (25 amp) and I'm trying to determine if its functioning correctly or if it needs to be replaced. Its connected to a single 12v bank of 6 6v trojan t105 batteries. When charging the charger drops the current way before reaching 14 v it never seems to exceed 13.3v in float mode or any other mode. I have the potentiometer inside turned up for the max duration of charge but it always drops current well before 10 hrs is up. I'm measuring voltage with a victron monitor and have verified its readings with a multi-meter. Is the charger malfunctioning? Shouldn't I be seeing 14.4v charging and 13.4 in float? Also when the refrigerator kicks on (7amps) the float voltage drops to ~13.15. I'm worried this charger might be chronically under charging my batteries.

As an aside I'm posting this here because I have called and twice emailed newmar with no response. I was thinking it might need to be repaired but since they won't talk to me I'd rather replace it if needed.
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Old 21-06-2017, 16:28   #2
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Re: Is my Battery Charger Failing

Don't know your charger, but I would suspect that a 25A charger will never achieve 14.4v bulk with your 6 trojan bank unless the bank was essentially fully charger to begin with. Try measuring current. If it is putting out 25A even in float, then it is doing all it can.
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Old 21-06-2017, 16:39   #3
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Re: Is my Battery Charger Failing

It only puts out the full 25 amps for a few hours then cuts current down to a few amps above whatever the load is.
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Old 21-06-2017, 17:50   #4
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Re: Is my Battery Charger Failing

Yes likely the charger, but verify with a known-good charger, it may also be something with the bank. If necessary test individual pairs or cells.

How old is the bank? How long since the last 20-hour load capacity test? A trojan dealer should be able to arrange one for free.
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Old 22-06-2017, 17:01   #5
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Re: Is my Battery Charger Failing

What's likely happening is that the charger is pumping out all the amps it can until its "absorption" timer expires and puts it in float mode. Unfortunately, that isn't long enough to fully charge your 675 amp hour bank of T105s. The rule of thumb is that you need a charger capable of putting out 25% of the capacity of your bank in amp hours, or about 169 amps. It needn't be that high, 100 amps would do, but 25 is way too little.

More advanced (read programmable) battery chargers either allow you to set the length of the absorption phase or the capacity of the battery bank (so that it knows to switch to float mode when the charge rate drops to 5% of capacity).

Anywho, Newmar makes good reliable stuff, but their battery chargers tend to be pretty basic. I recommend Magnum inverter/chargers. Still made in the USA.

Scott
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Old 22-06-2017, 18:00   #6
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Re: Is my Battery Charger Failing

Wow, totally missed that 675AH bank.

Amazing that a 25A charger ever worked well, maybe when only drawing down a little, or long charging periods with very low loads.

With a FLA bank, 10% would be low, 15% enough, 20% ideal.

Both the Sterling Power ProCharge Ultra and ProMariner ​Pronautic P series will let you optimize setpoints for all types of bank chemistries, pretty future proof.
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