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Old 08-03-2020, 10:15 AM   #1
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ambient temperature effect on chargers

We are just starting the process of replacing our old Onan 7.5 MDJE aka: Mr. Shaky, with a new NL 6kw. We've also been researching replacing our Xantrex Freedom 30 with a Magnum MS 2812. In reading the quite comprehensive owner's manual for the Magnum, I came across a graph showing the effects of ambient temperature on charger output and was surprised by the effects of what I would of assumed were normal environmental numbers on the output. At 79 deg the charger would put out it's full output of 125 amps. At 88 deg it would be reduced to 105 amps and at 97 deg 90 amps. This could seem to explain why in the bulk stage our present charger would start off at 130 amps and continue to fall before reaching the set voltage to switch to the absorption stage. This being with, as I understand it, a continuous current charger.

Our inverter is mounted in an area behind a large cabinet in the MSR. There is a large grill at the bottom of the enclosure that allows air into the area from the cabinet. Unlike the Magnum manual, the Xantrex installation manual is very vague about ventilation. When we go out this week, I'm going to take some temp readings of the ambient air as the charger warms up. I'm thinking about adding a temp controlled muffin fan in the top of the enclosure to improve the airflow.

In searching the Forum, I couldn't find any reference to this particular problem and thought I would throw it out there for discussion and comments.

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Old 08-03-2020, 10:51 AM   #2
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If there is only a grill at the bottom of the cabinet the charger is mounted in I’m afraid the charger will be able to get very hot during operation. If you can somehow provide another opening at the top of the cabinet that would make a huge difference. My own ProMariner 60 amp charger also warns that at temps higher than 113 the charger will operate at reduced output or even shut down if it gets too hot.

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Old 08-03-2020, 11:02 AM   #3
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We are just starting the process of replacing our old Onan 7.5 MDJE aka: Mr. Shaky, with a new NL 6kw. We've also been researching replacing our Xantrex Freedom 30 with a Magnum MS 2812. In reading the quite comprehensive owner's manual for the Magnum, I came across a graph showing the effects of ambient temperature on charger output and was surprised by the effects of what I would of assumed were normal environmental numbers on the output. At 79 deg the charger would put out it's full output of 125 amps. At 88 deg it would be reduced to 105 amps and at 97 deg 90 amps. This could seem to explain why in the bulk stage our present charger would start off at 130 amps and continue to fall before reaching the set voltage to switch to the absorption stage. This being with, as I understand it, a continuous current charger.

Our inverter is mounted in an area behind a large cabinet in the MSR. There is a large grill at the bottom of the enclosure that allows air into the area from the cabinet. Unlike the Magnum manual, the Xantrex installation manual is very vague about ventilation. When we go out this week, I'm going to take some temp readings of the ambient air as the charger warms up. I'm thinking about adding a temp controlled muffin fan in the top of the enclosure to improve the airflow.

In searching the Forum, I couldn't find any reference to this particular problem and thought I would throw it out there for discussion and comments.

Tator
Our Victron 3000 watt inverter is under the setee and can get hot. I have a pancake fan that turns on at 80 F and blows the hot air outside.

Inverters will reduce output due to temperature of the inverter and/or battery. If the inverter becomes too hot it will shut down.

Had a Magnum 2812 catch fire several years ago. I described what happened in a post. There are several reports on the web about Magnum 2812 catching fire in boats and RV's.

Magnum is no longer the same small innovative inverter manufacturer started by ex-Heart engineers since it was purchased by Sensata several years ago. I quit being a dealer for Magnum products after the fire. I now sell Victron inverter/chargers.
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Old 08-03-2020, 11:22 AM   #4
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A well ventilated space with a decent sized exterior fan providing fresh air is desirable but not always easy to do. Our ER located M2812 starts out at 125 amps following a day's cruise with ER temps between 80-90F with ventilation fan on. Works fine in general.
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Old 08-03-2020, 12:11 PM   #5
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I would add a top bent at a minimum. If you can add a temperature controlled fan that would be the best solution. Make sure you mount the fan on some soft rubber mounts since it is in the master and on quiet nights you will hear it. We have an icemaker in out motorhome that was very hot in the walkway next to it. I added a temperature controlled fan the area by the icemaker was much cooler.
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Old 08-03-2020, 01:02 PM   #6
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To respond to one of your questions: I don't believe it is unusual for chargers to be de-rated at higher ambient temperatures.
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Old 08-03-2020, 01:29 PM   #7
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Thanks for the replies. I wasn't so much surprised at the de-rating, just at how low the temps were for the de-rating.

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Old 08-03-2020, 01:51 PM   #8
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Thanks for the replies. I wasn't so much surprised at the de-rating, just at how low the temps were for the de-rating.
Just for comparison, I looked in the manual for a relatively inexpensive Victron charger (had manual on hand). The ratings are in C which I converted to F

1) Full rated output up to 104F

2) For every ~2F above 104F de-rate another 3%

3) So for example at 125F it would be de-rated by about 33%, which is fairly substantial.

So if your figures are F, I see what you mean because your current charger seems to start de-rating at a fairly low temperature.
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Old 08-03-2020, 02:25 PM   #9
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Yes, you want to keep it as cool as possible.
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Old 08-03-2020, 02:42 PM   #10
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Just for comparison, I looked in the manual for a relatively inexpensive Victron charger (had manual on hand). The ratings are in C which I converted to F

1) Full rated output up to 104F

2) For every ~2F above 104F de-rate another 3%

3) So for example at 125F it would be de-rated by about 33%, which is fairly substantial.

So if your figures are F, I see what you mean because your current charger seems to start de-rating at a fairly low temperature.
The figures were for the Magnum 2812. I don't have figures for my current Freedom 30. The Victron seems to be better on that concern. I will be looking at a Victron as well.

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Old 08-03-2020, 03:48 PM   #11
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The figures were for the Magnum 2812. I don't have figures for my current Freedom 30. The Victron seems to be better on that concern. I will be looking at a Victron as well.

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PM me and I'll quote you prices on the Victron inverter/charger.
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Old 08-03-2020, 07:08 PM   #12
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It's worth keeping in mind that when your charger is heating up during high output, it is very likely your batteries are heating up as well. Unless you have temperature monitor on your batteries which reduces charger output, cooling your charger artificially may cause damage to your batteries.

I recently swapped to a Victron mains charger and MPPT controller. Great products at good prices. (no affiliation)

I also acquired a great booklet from Victron which provides clear explanations on how best to set up a generic charging system on a boat.
Here's the soft copy:
https://www.victronenergy.com/upload...limited-EN.pdf
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Old 08-03-2020, 07:38 PM   #13
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It's worth keeping in mind that when your charger is heating up during high output, it is very likely your batteries are heating up as well. Unless you have temperature monitor on your batteries which reduces charger output, cooling your charger artificially may cause damage to your batteries.
Are you referring to temperature compensation? (That's the only temperature probe/wire/thing I'm familiar with that goes from a charger to a battery bank.) Speaking of lead acid batteries here, not lithium.

If so, I don't think that reduces amperage, per se. Rather it adjusts the absorption voltage to be the equivalent of the voltage one has chosen for the default 77F (higher voltage when batts are cooler; lower when batts are warmer). So say you had 14.4 volts set as your absorption. That is at 77F. If the batteries are cooler the "equivalent" voltage might be 14.8 or 15 volts. If they are warmer there would be an equivalent reduction to below 14.4. Hence why temp comp is important because otherwise your carefully programmed absorption voltage is meaningless unless the batts are at 77F.

In the absorption stage it's constant VOLTAGE [Mod Edit] and diminishing amperage until the batteries are full.

Or are you saying there are chargers that reduce bulk amperage via a temp probe? (Bulk being constant amperage, rising voltage.) Is that necessary from the batteries' perspective?

I thought when chargers "de-rated" their output in heat, it was a reduction in output amperage just because chargers are less efficient when it is hot.
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Old 08-03-2020, 08:19 PM   #14
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I think modern chargers have temp sensors bedded in/near the critical semiconductors. Automatically reduce output to keep the critical bits below a critical temp.
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Old 08-04-2020, 02:52 AM   #15
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I made a stupid typo above and can no longer edit it. I said:

Quote:
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In the absorption stage it's constant current, and diminishing amperage until the batteries are full.
When I meant to say:

In the absorption stage it's constant VOLTAGE, and diminishing current (amperage) until the batteries are full.

Sorry
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Old 08-04-2020, 03:57 AM   #16
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Frosty,
Yes I was referring to the battery temperature compensation. As you said - high battery temperature will reduce charging voltage a set amount.
Reduced voltage will result in lower power (and heat buildup in charger and batteries) if current is constant.
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Old 08-04-2020, 04:34 AM   #17
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Frosty,
Yes I was referring to the battery temperature compensation. As you said - high battery temperature will reduce charging voltage a set amount.
Reduced voltage will result in lower power (and heat buildup in charger and batteries) if current is constant.
Yes but only during the absorption stage is when temp comp adjusts the voltage. That stage is constant voltage/diminishing current (not constant current) and by then you are long past using anywhere near the rated amperage of the charger. How can this possibly cause heat build up in the charger or batteries due to temp comp?
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