Wiring idea for charging house batteries

Kiltym

Active member
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.
 

onemanvan

Active member
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...
 

calbiker

Well-known member
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.
 

Kiltym

Active member
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.
 

calbiker

Well-known member
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.
 

Kiltym

Active member
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/
 
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Kiltym

Active member
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.
 

Attachments

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.
 

onemanvan

Active member
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-to-dc-on-board-battery-charger/

In hind sight - FWIW - one of these plus a separate dedicated solar charge controller might be a better solution...
 
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Thank you for the reply onemanvan.:thumbup: Comforting to know that I understand how to install a flawed piece of equipment correctly. :thinking: ..the "yo-yo" mode you describe is very disappointing to say the least. :thumbdown:

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.
 

Kiltym

Active member
For us, with two panels in series (40+ volts), the 1250 is working adequately. I think having lower voltage from a single panel adds to the issue onemanvan described. The original issue we had with the 1250 was resolved with a firmware update.

At the moment we are satisfied with the 1250 performance. If the 1230 does not have the update, it will not perform properly when charging from solar.

The issue now present is mitigated with the higher voltage as we do not seem to see the switching sources as profoundly as onemanvan has.
 
Reading your previous posts about your installations, it appears neither of you installed the ignition sensing wire...could/might the inclusion of that wire allow the DMT to "know" with certainty when the alternator input is not available and therefor not enter the "yo-yo" mode searching for the better of the two inputs ?
 

onemanvan

Active member
Reading your previous posts about your installations, it appears neither of you installed the ignition sensing wire...could/might the inclusion of that wire allow the DMT to "know" with certainty when the alternator input is not available and therefor not enter the "yo-yo" mode searching for the better of the two inputs ?
I doubt that would make any difference. If the engine isn't running then the ignition sense wire will have zero volts on it. Which is the same as if the ignition sense wire was not connected. For our application I don't think the ignition sense wire offers any value added. When the engine is running both the 1230 & 1250 automatically switch over to alternator input and stay there until some seconds after the engine is turned off.

To clarify:

There are two different problems - similar in nature.

DMT1230 - 'yo-yo' mode - It slowly ramps up to maximum ( for example 6 amps ) then quickly drops to zero and repeats endlessly...

DMT1250 - 'flip-flop' mode - 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.

With regard to the 1250 'flip-flop' mode I can hear the relay clicking and clacking as the unit endlessly toggles back and forth between inputs - very irritating. It only exhibits this behavior under low light conditions. Early morning, late evening, shade, clouds. These are situations where you're not really losing any solar gain because there's so little to lose! If you have a 200 watt panel with a VOC greater than 30 volts then you might notice - as Kiltym did - that this problem is lessened. My VOC is typically less than 20 volts.

With regard to the 1230 'yo-yo' mode the relays are not clicking and clacking. The unit is fixed to the solar input. This condition occurs even in full sun with good solar potential. However it wastes the majority of that potential because it's constantly ramping up and down!

Hope that helps to clarify.
 
Thank you, yes that does clarify the issues. Unfortunately the increased clarity is painting a far less than desirable picture. If the 1230 is exhibiting the ramping up and down constantly under solar input, as I think you are saying, the unit is not worth installing IMO. The primary objective for me is to have a reliable, effective source of battery charging while boondocking, which is what I do almost exclusively.

I sent Ricardo an email last night asking about the latest status of the issue.

Sounds like I may need to look for another multi-input B2B charger, if one exists, or go to separate B2B and MPPT chargers.
 

onemanvan

Active member
No doubt there are some DMT1230/1250 owners who have never noticed or perhaps experienced the 'yo-yo' mode. I almost exclusively dry camp - for four months out of the year every year ( June thru Sept ). I have two 100 watt 32 cell panels in parallel on the roof and one 100 watt 32 cell portable. I have two six volt agm's in series ( one of them is going bad ). There are many variables for the charge controller to deal with under these ever changing circumstances. For me - the 'yo-yo' mode usually seemed to occur when I only had around 6 amps of solar gain and the state of charge was around 80%. It's difficult to define the exact values because I'm not watching them constantly. I guess what I'm trying to say is the 'yo-yo' mode is an intermittent issue dependent on many factors. I'm also guessing that what's happening internally is the unit hit's a point where it's not sure what charge mode it should be in - IE: bulk, absorption or float. Apparently the algorithm it's using to determine SOC requires that it disconnect the charger output from the battery then gradually ramp up the output to figure out what the SOC is. Under some circumstances the results are apparently inconclusive. So it try's again - and again - and again. If the variables remain the same - for example 6 amps of solar potential with the fridge cycling on/off and perhaps the fantastic fan running - then it remains in the 'yo-yo' mode. Switching the unit off then back on sometimes resets the 'brain'. Then it starts the charge algorithm anew - beginning with bulk.

IMHO Kisae is charging a premium price for mediocre hardware/software. I believe there is better value for the money to be had. I'm certain there are better solar charge controllers! I recently installed a solar setup for my brother. Two 100 watt 32 cell in series with the Victron MPPT 75/15 Smart Solar charge controller.

https://www.amazon.com/gp/product/B075NQQRPD/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

If you have a 200 watt 72 cell panel then the MPPT 75/15 would probably be a good match. I really liked the bluetooth app. It's very user friendly and provides a wealth of information! And it's highly configurable.

As for a dc to dc charger - both Victron and Votronic offer good ( but expensive ) options. I really can't speak for the Renogy. The price is right but how good the hardware/software is remains to be seen...

If your primary objective is to have a reliable, effective source of battery charging while boondocking then perhaps all you really need is a good solar charge controller. I can definitely recommend the Victron.
 

autostaretx

Erratic Member
I doubt that would make any difference. If the engine isn't running then the ignition sense wire will have zero volts on it. Which is the same as if the ignition sense wire was not connected... .
That is not necessarily safe to assume...

If there's anything else acting as a load on that ignition-sense tap point, then it will (probably) be held to zero when the engine is off.

But if the ignition sense wire isn't connected to *anything*, then it becomes a "floating" input.
The Sprinter's EK1 "ignition on" post probably acts this way (opened relay contact when off).
And what happens then depends upon the 1230's input circuitry design.

If it goes straight into a TTL (transistor-to-transistor logic) gate, then it will float "high" ... unless the input had pull-up or pull-down resistors as part of the 1230.

It's usually safer to tie an unwanted/unused input directly to a known level/source (such as ground or frame, if they're also serving as the negative "feed") so that surprises (or pick-up RF signals) don't sneak in the wire.

Of course, if the 1230's book says it's safe to leave the ignition sense floating, that's one thing. But if they don't cover that approach, it's sometimes better to assume the worst.

--dick
 
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IMHO Kisae is charging a premium price for mediocre hardware/software. I believe there is better value for the money to be had. I'm certain there are better solar charge controllers! I recently installed a solar setup for my brother. Two 100 watt 32 cell in series with the Victron MPPT 75/15 Smart Solar charge controller.

https://www.amazon.com/gp/product/B075NQQRPD/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

If you have a 200 watt 72 cell panel then the MPPT 75/15 would probably be a good match. I really liked the bluetooth app. It's very user friendly and provides a wealth of information! And it's highly configurable.

As for a dc to dc charger - both Victron and Votronic offer good ( but expensive ) options. I really can't speak for the Renogy. The price is right but how good the hardware/software is remains to be seen...

If your primary objective is to have a reliable, effective source of battery charging while boondocking then perhaps all you really need is a good solar charge controller. I can definitely recommend the Victron.
Thank you for the Victron suggestion onemanvan, their equipment seems to get lots of positive press. The solar panel currently at the top of my list is actually 200W with 36 cells not 72. it's at the top of the list purely because it's the largest single panel that I can find to fit my available roof space.
 

luvwagn

Member
Dumb Q - where is this mythical K52 relay located? I figured out which red wire in the aux batt cabinet was from the alternator (the only one live with engine running), and ended up running it directly to my DC-to-DC converter. If I go down the path of using the MeanWell wiring (so that DC-to-DC can get voltage when on generator, on 120V shore-power, or from ALT), I understand to just tape off the ALT wire in the aux batt cabinet? But still curious where that comes from (I thought it was a direct feed from ALT).

Also, for a switch into the DC-to-DC, i'm still a bit fuzzy for why/when i'd use the switch. Ideally, i don't want to think about it, and I want to just use AC regardless of engine running, generator, or 120V - without thinking to mess with other switches. Would I only use the switch on input to DC-to-DC to turn it off so that its LEDs aren't sucking down power from the starter battery? Or is the relay off without engine, and there's no voltage to that wire anyways (input side), and in reality the unit is getting power from the downstream (aux) batteries in order to light up its charge-indicator and charging-profile indicator? (Renogy DCDC50S)
 

onemanvan

Active member
For anyone interested in fishing/routing wires/cables from the Mean Well power supplies ( Kerstner converter in water heater compartment) to the coach battery area ( fresh water tank - OEM battery charger ) - for example when adding a B2B charger ( DMT1250 etc... ).

Or when re-purposing the external telephone jack for portable solar panel and needing to route wires from that outlet/receptacle to the coach battery area.

Here are a few pictures I took today that might help when deciding how to fish/route the wires.

Note: Some dis-assembly required:)

Getting from the battery area to the trash can closet ( under the sink ).
Follow the piece of PEX tubing I poke in there for reference.
In the picture on the left you can just make out the PEX tubing in the lower right corner of the image.

PXL_20210208_180626636-COLLAGE.jpg

Getting from the trash can closet ( under the sink ) to the circuit breaker compartment .
Follow the piece of PEX tubing I poked in there for reference.

PXL_20210208_180818208-COLLAGE.jpg

Getting from the compartment where the circuit breakers and transfer switch are located to where the black tank is.
Follow the piece of white PEX tubing ( and/or the red wire ) I poked in there for reference.

PXL_20210208_174820287-COLLAGE.jpg


Getting from where the storage area where the black tank is located to the water heater compartment.
In these pictures follow the red wires.

PXL_20210208_181141952-COLLAGE.jpg
 

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