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Old 03-05-2015, 19:25   #1
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Battery charger/power wire

Working on my sisters electrical system that has the power panel that houses the 120VAC to 12VDC converter. The panel is located a good 15' from the battery bank with 8ga wire. The panel originally consisted of a single rate charger, thus she has gone thru 2 sets of batteries from overcharging. I talked her into upgrading the charger (converter) part of the power panel to a 4 stage charger. After all was hooked up and the charger was in the high charge rate mode, I measure 14.6V at the charger leads, but at the batteries them selves I was only getting 13.6 volts. I'm thinking the battery cables from charger to batteries need to be increased to get the voltage loss down. This all I understand

But my question is, until the larger cables are installed if I believe this is the fix, will the charger cycle thru the 3 stages normally? I'm not sure if the charger will get a true battery voltage reading due to the voltage loss and stay in a high charge rate mode and not drop down to the 2nd charge stage, or is she just looking at longer recharge times?

BTW, this is in her 5th wheel horse/ travel trailer, so moving the power panel which consist of all the AC circuits and breakers, and all the 12vDC fuses and wiring, along with the power convertor itself are all housed in this panel, and batteries are located in a battery box up front outside at the 5th wheel hitch, so neither are relocatable.
Sorry its not boating, but being boats and RVs very similar, I didn't want to sign up to an RV board for this 1 question. 12V power draws are lights, AC/DC fridge, AC/DC water heater electronic ignitor, fresh water pump, radio, CO detector.

Thanks in advance
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Old 03-05-2015, 20:22   #2
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Re: Battery charger/power wire

Forgot to mention, the converter/charger is a 45A unit. Also, I may be incorrect on the battery cable size, but the voltage loss is as stated.
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Old 03-05-2015, 20:33   #3
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Re: Battery charger/power wire

At 45A on AWG 8 wire that voltage drop is about right. So bigger wire is the correct answer. Also, if there isn't a 75A ANL type fuse at the battery positive charging wire there needs to be one.

The charger will still charge the batteries but it will take considerably longer and it may not be optimal for longest battery life. If the charger has a remote battery voltage sensing feature that can help in this situation. But you have to run two more wires from the batteries back to the charger to get that to work.

One issue in this application is charging whilst everything is running. If the fridge and other gadgets are on when charging then the charger has to be pretty smart to work in this type application. It can't tell the difference between what current is used to charge the batteries and what current is used for running all the loads. Many "dumber" chargers will never go into "float" mode because these extra loads convince them that the batteries are still not charged. So even some so-called smart chargers still burn up batteries because of that.
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Old 03-05-2015, 21:14   #4
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Re: Battery charger/power wire

Thanks for the reply. No, there are no fuses at the batteries. There are leads for the main power panel, the automatic awning, and electric jack, all directly to the battery post, none are fused. I have already mentioned we need to fuse these in the battery box. I errored on the water heater description. It is a 120VAC/propane gas unit, that has a 12vdc electric ignitor. Not that this makes a difference, just prefer for all info to be correct to best of my recollection.

Yes, I have read about the charge rate dependent upon current draw issue. I assumed this would be no different than when my boat is plugged into shore power where the charger is also acting as a 12V power supply splitting output power between the batteries and accessories in use.
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Old 03-05-2015, 23:09   #5
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Re: Battery charger/power wire

at the full 45a you will get voltage drop. but as the batteries charge. and less current is charging. the voltage drop will also drop. as the batteries get full the correct voltage will be at both charger and batteries.


still nice to have the right size cables and proper bulk charging voltage though
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Old 04-05-2015, 20:53   #6
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Re: Battery charger/power wire

Thanks.
I believe it best to have a fuse on the main power wire at each end---Converter/charger end and also at the battery terminal. This would protect the wire if the pos battery wire would short out. Being how that power wire can receive voltage from either the battery or from the charger if it was on at time of short. Correct? Same size fuse too?
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Old 04-05-2015, 21:27   #7
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Re: Battery charger/power wire

I see the edit feature has a short time frame.


Disregard above post. A FAQ on the converter site states the converter has built in circuit protection in the event of a short. So I will only be fusing at the battery end.
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Old 04-05-2015, 21:39   #8
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Re: Battery charger/power wire

How hot do the wires get? You are greatly undersized and the system is very dangerous. Think fire hazard...
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Old 04-05-2015, 22:01   #9
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Re: Battery charger/power wire

AWG 8 at 45A is not a fire hazard as long as the terminations are clean and tight. The power dissipation is about 1.5 watt per foot. That will get warm but not burn your finger hot.
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Old 04-05-2015, 22:12   #10
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Re: Battery charger/power wire

Quote:
Originally Posted by transmitterdan View Post
AWG 8 at 45A is not a fire hazard as long as the terminations are clean and tight. The power dissipation is about 1.5 watt per foot. That will get warm but not burn your finger hot.
No, it's really pushing it. 8AWG is only good for 10 feet total at 3% voltage drop for 40 amps.

Silly really to use anything less than 6.

Use the published tables for wire sizing.

For goodness sake.

What's so hard?

They're even available on the (gasp!) internet:

https://www.bluesea.com/support/reference

What's your entire boat worth to you? eace :
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Old 04-05-2015, 22:23   #11
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Re: Battery charger/power wire

The 8 gauge wire was already there. It's not a new installation and difficult to change right now. The voltage drop (1V) doesn't matter much for a charging circuit. It matters for loads but not so much for charging. It just makes the charging take a little longer. Lighten up on the guy, his sister's horse trailer isn't going to turn into a Roman candle.
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Old 05-05-2015, 00:31   #12
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Re: Battery charger/power wire

a 45 amp converter. Is it an Iota or a Progressive Dynamics?

These do not need to be located in the power center. You can move the converter closer to the batteries.

it is well known in the RV world that getting these things to put out their full rated amperage requires they be close to the batteries over thicker wiring.

If the converter is a Wfco, short fat cabling is no guarantee of getting the charger to try for 14.4v either.

These converters do not have issues powering loads while charging batteries, their absorption stages are more on a timer rather than an amp load. Their biggest issue, like most automatic 3 4 or 22 stage 'smart' chargers, is premature dropping of voltage to inadequate levels to complete the battery charging.

Progressive Dynamics allows the use of a 'pendant' to force the 14.4 stage to last longer, but if you have 1 volt of drop to the batteries, well, I've seen my battery fail to get above 1.250 specific gravity when held at 13.6 for 5 days. It took an hour on day 5, at 14.7v before it rose above 1.270.

Moving that converter to the batteries is your solution to at least a somewhat respectable battery life.

Also, RV wiring terminations are absolutely horrid. Their crimps look like they use pliers and Harbor Freight steel ring terminals
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Old 05-05-2015, 07:58   #13
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Re: Battery charger/power wire

Sternwake, I take it you are familiar with RVs
The power center itself is a Parallex. The converter upgrade unit is indeed a PD. a direct replacement with no modifications. We could move the converter closer to the batteries, but not the whole power center. That would require gutting and a total rewire of the whole trailer, AC and DC wire. Don't see this as an option. Im hoping going up in wire size will work. 10 min job for this. Plus I can test this by simply running a 2nd wire to batteries seeing if it helps the voltage drop before going bigger
While she has had nothing other than batteries being overcharged from the old charger, I'm taking this opportunity to improve on the areas I feel the RV world rigging standards fall short ( no fuses at batteries), making it both problem free and safe.
Thank you all.
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Old 05-05-2015, 08:16   #14
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Re: Battery charger/power wire

For clarification, the converter is not a stand alone item as some of the models are. It's just the 'guts' without a housing. It replaces the old charger itself. The charger, ac wiring and breakers, DC wiring and fuses, and the incoming shore power cable, all reside within the housing. Thus a single power center unit and moving/ separating any of the components isn't possible
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Old 05-05-2015, 12:39   #15
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Re: Battery charger/power wire

Ah the PD 9100 series. I was thinking the enclosed 9200 series.

I just replaced an unenclosed Wfco with an iota dls-45 in a friends RV. He rarely requires fast charging, and I did not bother upgrading the 8awg wiring, whose full circuit length was probably 20'.

The Wfco allowed his 'marine' batteries to last 5 years, and he had no idea that batteries should be kept fully charged.
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