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Old 02-28-2018, 09:20 PM   #61
Kiltym
 
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Default Re: Wiring idea for charging house batteries

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Originally Posted by onemanvan View Post
The B2B I purchased ( DMT1230 ) does not have a dedicated sense wire. IE: You tell it what voltage to output and it compares that to the voltage at the B2B charger.
So if I set the charger to charge Bulk at 14.9, the batteries should receive the 14.7 since the charger doesn't know better. I suppose the concern is that as the amps drop (absorption), the voltage will actually increase (because of less voltage drop on the cable) which is perhaps the issue I was missing as eventually at 10A it will be almost at the higher 14.9 voltage which is perhaps too high for the battery.



And the calcs you did on 10' is 2x the length I am using. I think you would need to enter 4.5' as the length on the calculator "* Please use one-way distance to the load. Not round trip distance.". Or am I missing something.... ? I assumed I could take total length and divide by 2.

If you were just using the 10' as an example, all good, but wanted to be clear that it is longer then what would be needed in our Westy assuming a mounting location around the sink.

I think I will stick with the 6AWG. Should be fine, especially after the revlation that as the amps taper off, the loss is less, and it will push the batteries up to the "correct" voltage by the time it's finished. Yes, some performance loss (which would translate into time to charge) vs a 2AWG cable, but doesn't seem worth it to me. But am happy to be convinced otherwise as I have not ordered the cable yet.
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Old 02-28-2018, 10:14 PM   #62
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Default Re: Wiring idea for charging house batteries

I was just using 10 feet as an example. The key point being - as the battery approaches full charge ( absorption phase ) the current will taper off - such that wire size becomes less critical.

Oftentimes you will see documentation that refers to bulk phase as constant current and absorption phase as constant voltage.

In the bulk phase voltage is not so important - basically anything between 13~14 volts will provide enough 'push' to transfer whatever current is available into the battery.

In the absorption phase you want to bring the battery up to a certain voltage and no higher.

It's sort of like blowing air into a balloon. Where pressure is synonymous with voltage and volume of air is synonymous with current.

When the balloon is empty it takes very little pressure to push a large volume of air into the balloon ( bulk phase / high acceptance rate / constant current ).

As the balloon stretches tight - near maximum capacity - it takes more pressure to push a lesser volume of air into the balloon ( absorption phase / low acceptance rate / constant voltage ).

Too much pressure and POP...
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Kiltym (02-28-2018)
Old 02-28-2018, 10:49 PM   #63
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Default Re: Wiring idea for charging house batteries

You need to account for a round trip, not just one way. 6 awg charging cable at 50A is grossly undersized. You pay the big bucks for a good charger and then undermine it with sub-par cable.
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Old 02-28-2018, 11:04 PM   #64
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Default Re: Wiring idea for charging house batteries

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You need to account for a round trip, not just one way. 6 awg charging cable at 50A is grossly undersized. You pay the big bucks for a good charger and then undermine it with sub-par cable.
I understand a circuit is the round trip, which I wrote out earlier. 9’ total. With a chassis ground, its total for positive and negative cable runs AFAIK.

The calculator referenced however wants only a one-way length, and presumably it does the math for the “round trip”. So to use that calculator, one would enter 4.5’ AFAIK. If I am wrong about this, please someone correct me!

Based on multiple calulcators (and the above understanding), I have to disagree with your assessment about 6AWG on a 50A charger with such a short cable run. If you can point me to something contrary, please do as I would be interested to read/understand it.

The voltage total drop is 1%. I feel this is quite adequate.
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Old 02-28-2018, 11:49 PM   #65
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Default Re: Wiring idea for charging house batteries

I was under the impression you had a longer run. That said...

If you only have 10' round trip then a 6 awg cable will have the following drop:
V = 0.4 mohm/ft * 10 ft * 50 A = 0.2 V
That's a 1.4% drop from 14.7V.

A 2 awg cable has this drop:
V = 0.156 mohm/ft * 10 ft * 50 A = 0.078V
That's a 0.5% drop from 14.7V.

I always advocate less than 1% voltage drop.

What's the difference in cost?

10 ft of 6 awg welding cable costs $19.00, while 2 awg costs $24.50. $5.50 extra cost will give you a faster charge.

In addition, 6 awg cable is close to max ampacity. 60 deg C insulation is rated at 55A. 75 C insulation is rated at 65 A. This rating is when the ambient air is at room temp. I would not be comfortable with those slim margins.

2 awg is rated at 95A with 60C insulation.
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Old 02-28-2018, 11:57 PM   #66
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Default Re: Wiring idea for charging house batteries

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Originally Posted by calbiker View Post
In addition, 6 awg cable is close to max ampacity. 60 deg C insulation is rated at 55A. 75 C insulation is rated at 65 A. This rating is when the ambient air is at room temp. I would not be comfortable with those slim margins.

2 awg is rated at 95C with 60C insulation.
The cable I use would be rated for 105C. ABYC standards (marine), which is much stricter then cars, allows for 120Amps, according to Bluesea. After living many years on a boat, any wiring I do is per their standards. Tinned cable, etc....

“Recommended Wire
AWG 6

Capacity per ABYC Standards: 120 amps.
This wire selection is the result of applying ABYC Standards factors, additional derating factors, and allowable voltage drop.”

Anyway, I think I am fine, but agree, thicker is always better, can’t argue with the math!

For reference, capacity per AWG: https://www.coonerwire.com/amp-chart/

Last edited by Kiltym; 03-01-2018 at 12:00 AM.
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Old 03-25-2018, 04:06 PM   #67
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Default Re: Wiring idea for charging house batteries

I received the Kisae DC-DC charger last week. The new 50A version (DMT-1250) I had been waiting for.

I now have it installed, and is working perfectly.

IMO, finally, the converter and generator can be used for something useful :).

With the wiring from the Kisslinger relay to provide the source DC power, the system works great. Plugged into AC shore power, generator running, or driving the car, all goes through a solid 3-stage charge system, and all happens automatically.

I turned up the converter DC output to about 13.8V.

I disconnected and taped off the DC cable from the alternator/relay that normally charges the house batteries when the engine is running. Can easily be re-connected if ever needed.

I have flipped the breaker for the Westy charger to keep it turned off when on AC power. Otherwise it will try to keep the voltage > 14 when the new charger is in float mode and keeping the batteries at 13.6. This does lose the ability to trickle charge the engine battery, but I am not overly concerned about losing this function. If ever needed, simply flip the breaker to turn off the converter (turns off new charger), and flip back on the breaker for the Westy charger, and you can charge the engine battery if needed.

A few things to note:

1) The AC breaker that controls the Westy charger states it also controls the outlet for the microwave. However, when the breaker is off, the Westy charger is not working, which is good, but the microwave still has power. So something is mislabelled here, not sure it applies to all or not.

2) The little "plug" icon on the front computer comes from the Westy charger. So I do not see that icon with the Westy charger turned off.

3) And the front computer does not "sense" the new charger, so even when charging, the computer displays the battery icon indicating it is not charging (even though it is). If the engine is running, the icon goes away as normal, but when on AC power, it does not.

None of these are of concern, and should not effect anything, just pointing them out for future reference.

Attached is a photo of the install. I put it in the cabinet under the drain near the main battery switch.

Next step is solar panels, which is great as they can be plugged into the same charger and have one complete integrated charging system that is all automatic. I am very happy with the DMT1250 and the features it provides. As onemanvan pointed out, there may be some constraints with Lithium batteries, but for AGM or Gel, all is pretty good.
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Old 06-20-2019, 04:09 AM   #68
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Default Re: Wiring idea for charging house batteries

After reading the Kisae manual and this thread, I still have a few questions/confirmations about installing the Kisae DMT1230 in our Westfalias. I'm not an electrician, just a meticulous monkey who can follow directions well.
Onemanvan and Kiltym, unlike you guys, I will be using the Kisae simply for alternator and solar panel charging of one AGM battery bank, as I have removed my generator, roof top air conditioner and all the associated electrical equipment from the water heater closet.

1. The - cables from both the DMT's CH3 and CH1- terminals connect to the chassis ground stud just to the rear of the shunt above the OEM AC Westy charger ?
2. The DMT's "unit ground" can be jumped to the CH1- terminal as all - terminals on the DMT are in common ?
3. The three above - cables can all be 10awg ?

4. The red 6 awg cable with the 100 amp fuse coming from the Sprinter's alternator via the under seat isolator, currently connected to the house batteries, gets connected to the DMT's CH3 + terminal?
5. When installing the required 50 amp circuit breaker in the " red 6 awg cable", the original 100 amp fuse in the "red 6 awg cable" should be removed ?
6. The + cable connecting the DMTs CH1+ terminal to the house battery bank should be 6 awg cable and should pass through a 40 amp circuit breaker ? (cable length will be 3' or less in my install)
7. The black 6 awg cable currently connected to the negative side of the house battery bank, which I believe runs straight to the shunt above the OEM AC Westy charger should be left in place ?

CH3 = Alternator/Start Battery (input)
CH2= Solar Panel (input)
CH1= House Batteries (output)

Thank you.
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Old 06-20-2019, 06:23 PM   #69
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Default Re: Wiring idea for charging house batteries

That all sounds about right. You're correct that all of the ground terminals on the DMT1230 are in common. Therefore you only need one 6awg cable connecting the common ground bus of the DMT1230 to the Westy chassis ground post. The 'unit ground' can be jumpered to one of the ground terminals if the 6awg ground cable is a short run - ie: less than 3 feet.

Be forewarned: Both Kiltym and myself have experienced a problem with the DMT1230 wherein the charge algorithm sometimes behaves strangely. IE: it seems to go into a hunt and seek mode ( yo-yo ) when the solar charge current and/or voltage is relatively modest. It slowly ramps up to maximum ( for example 6 amps ) then quickly drops to zero and repeats endlessly... For me it seemed to exhibit this behavior mostly in absorption ( or possibly float ) phase. I could sometimes break it out of this endless loop by turning it off then back on. Whether of not you experience this issue might depend on how many solar panels you have and how they are connected ( series vs parallel ).

Ultimately both of us ( separately and at different times ) complained to Ricardo at Kisae and he exchanged our units with new DMT1250's which have revised software. So they are aware of the issue! At the time ( six months ago ? ) the new software was only available for the DMT1250 model.

Since installing the replacement 1250's we have both noticed that the 1250 exhibits a similar problem. It seems as though the 'brain' is looking at the solar input and when it's very low it switches over to the alternator input to see if there is more power available there. If it's not then it switches back to solar. Again it goes into an endless 'hunt and seek' cycle until the solar input power is greater than 'something' - hard to quantify exactly where the crossover point is.

While this 'hunt and seek' AKA 'yo-yo' mode might simply seem annoying it can in fact be very counter productive. With respect to the 'yo-yo' mode I once observed it going into this mode around noon one day and staying there all day. I suppose the 1230 had just gone into absorption mode. The battery bank was probably at around 80% charged. I was only getting about 6 amps of solar gain. The fridge was of course cycling on and off and maybe I had the fantastic fan running. The never ending 'yo-yo' mode - coupled with modest solar gain - coupled with loads - resulted in ZERO progress towards completion of the absorption phase!

I've recently noticed that Renogy now offers a dc to dc charger - 20 or 40 amp models: ( currently sold out )

https://www.renogy.com/renogy-12v-dc...ttery-charger/

In hind sight - FWIW - one of these plus a separate dedicated solar charge controller might be a better solution...

Last edited by onemanvan; 06-20-2019 at 08:43 PM.
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Robert Foster (06-21-2019)
Old 06-21-2019, 03:20 AM   #70
Robert Foster
 
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Default Re: Wiring idea for charging house batteries

Thank you for the reply onemanvan. Comforting to know that I understand how to install a flawed piece of equipment correctly. ..the "yo-yo" mode you describe is very disappointing to say the least.

FYI. I will be installing it with a single 200 watt solar panel, not that I think that will change the "yo-yo" mode you describe.

I'll probably send Ricardo an email to see what, if anything has changed in the last six months regarding this issue.
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