prelude
11th August 2019, 08:53 PM
Hi all,
Having only a simple relay (ie not a proper one) between my main and secondary batteries which has proven to be barely adequate for testing purposes I feel the need to fix and upgrade this setup in my P38.
I have:
fixed alternator output afaik, a minimum of 14volts
lead acid main battery, considering replacing it but not sure with what
hydraulic winch, ie. I do not need stupid amounts of power in the front
270ah of gel batteries as secondaries, might replace with different technology
no electrical setup to speak of as of yet
I would like:
hook up HF and other radio's to secondaries, have a full ham license so will be using it stationary
run my fridge, of course
decent charging of secondaries, both stationary and driving.
keep the ever so sensitive P38 main electronics to retain their preferred voltage levels.
I am probably going to:
travel for very long periods of time so no maintenance charge from the wall possible
have a solar panel or blanket
bring an ordinary switching power supply for charging
My questions:
should I go DC-DC
what size
what brand
The long version below :)
It seems that with certain battery technologies simply bridging the main alternator output to the secondaries through a relay (heavy duty) and a voltage sensing circuit is simply enough. My current testing with my admittedly lacking setup has shown that just dumping power into the secondaries might not maintain them well enough.
This is where a DC-DC charger comes in, these were designed to provide the same charging regimes that a multistage "from the wall" charger would normally provide. I like the thought of this since it would maintain my batteries as they were meant to. In the land of DC-DC there are a lot of differences and by now numerous brands on the market. In Australia you get that wonderfull redarc stuff and what not but down here our choices are more limited. A "local" brand here is ctek however and I have seen them being used here on the forum.
The main difference between a direct connection (relay or manual isolator) and a DC-DC charger is the amount of potential current that can be delivered to the secondaries, given enough wire diameter to handle it. On the other side of this same coin; smaller-ish cables from the front to the rear, since voltage drops across the wiring are handled by the charger in a DC-DC setup.
Currently I have gel batteries as secondaries. They were secondhand but free so who's complaining :) This type of battery is not suitable for high current charge or discharge. Large gauge wires and a large charging current are not applicable and a DC-DC charger would work nicely in this situation, I think. However... Seeing as these batteries were free, not new and I do have other needs from my electrical system it seems reasonable that I would change battery type at some point in the future. Lithium is only a consideration when weight really becomes a factor and in all other circumstances I think AGM or LeadCrystal would be the first contenders.
Both these battery types can handle large currents a common DC-DC charger quickly becomes to light to handle these currents. Redarc "recently" (could be over a year but I can't recall) brought out a 50Amp model but they are quite expensive and the only brand that produce one AFAICT. most common units from other brands are in the 20-25 amp range. So far, without scouring out every option on the intarwebs, I have found that ctek offers a nice option in their 140A offroad kit. 140A OFF ROAD (https://www.ctek.com/products/on-board/140a-off-road)
The concept of this kit is that it has a DC-DC charger up to 20 amps in the form of the D250SA and it has the ability to simply hook the mains up to the secondaries through the SMARTPASS 120. The way I currently understand how this works is that under normal circumstances, when the secondaries are empty the smartpass bridges over the D250SA and full current from the alternator will go into the secondaries, charging them with as high a current as they want/can absorb and by the time the voltage has raised and the amperage has dropped to a certain point the D250SA will kick in, taking over the rest of the charging. On paper this sounds to me as the best of both worlds.
Since this unit also has a MPPT controlled solar input that makes life even easier when stationary for a long time. I also figured that since solar is nothing more than a DC voltage source I would bring a switching mode power supply that could provide any voltage inside the input range of the solar input and I could charge the system when stationary and have mains power available. (disconnecting the solar panels at that time of course). A modified HP DL380 server power supply is small, reliable, auto sensing input voltage and can crank out a whopping 80 amps!
Now, I am not sure of redarc or national luna or any of the other manufacturers have similar solutions but in general I wonder what the "best" brand in this business is? ctek is widely seen around here with their 240V chargers and they seem to pretty much own this market, making me believe that since the product is not cheap it must be doing something right. One would assume that this translates well into the mobile solutions. The housing is plastic though and I would think a heat sink type housing would be preferable.
In any case, is there any information out there that my google-fu could not find or does anyone here have any experience on this subject?
Thanks for any input ;)
Cheers,
-P
Having only a simple relay (ie not a proper one) between my main and secondary batteries which has proven to be barely adequate for testing purposes I feel the need to fix and upgrade this setup in my P38.
I have:
fixed alternator output afaik, a minimum of 14volts
lead acid main battery, considering replacing it but not sure with what
hydraulic winch, ie. I do not need stupid amounts of power in the front
270ah of gel batteries as secondaries, might replace with different technology
no electrical setup to speak of as of yet
I would like:
hook up HF and other radio's to secondaries, have a full ham license so will be using it stationary
run my fridge, of course
decent charging of secondaries, both stationary and driving.
keep the ever so sensitive P38 main electronics to retain their preferred voltage levels.
I am probably going to:
travel for very long periods of time so no maintenance charge from the wall possible
have a solar panel or blanket
bring an ordinary switching power supply for charging
My questions:
should I go DC-DC
what size
what brand
The long version below :)
It seems that with certain battery technologies simply bridging the main alternator output to the secondaries through a relay (heavy duty) and a voltage sensing circuit is simply enough. My current testing with my admittedly lacking setup has shown that just dumping power into the secondaries might not maintain them well enough.
This is where a DC-DC charger comes in, these were designed to provide the same charging regimes that a multistage "from the wall" charger would normally provide. I like the thought of this since it would maintain my batteries as they were meant to. In the land of DC-DC there are a lot of differences and by now numerous brands on the market. In Australia you get that wonderfull redarc stuff and what not but down here our choices are more limited. A "local" brand here is ctek however and I have seen them being used here on the forum.
The main difference between a direct connection (relay or manual isolator) and a DC-DC charger is the amount of potential current that can be delivered to the secondaries, given enough wire diameter to handle it. On the other side of this same coin; smaller-ish cables from the front to the rear, since voltage drops across the wiring are handled by the charger in a DC-DC setup.
Currently I have gel batteries as secondaries. They were secondhand but free so who's complaining :) This type of battery is not suitable for high current charge or discharge. Large gauge wires and a large charging current are not applicable and a DC-DC charger would work nicely in this situation, I think. However... Seeing as these batteries were free, not new and I do have other needs from my electrical system it seems reasonable that I would change battery type at some point in the future. Lithium is only a consideration when weight really becomes a factor and in all other circumstances I think AGM or LeadCrystal would be the first contenders.
Both these battery types can handle large currents a common DC-DC charger quickly becomes to light to handle these currents. Redarc "recently" (could be over a year but I can't recall) brought out a 50Amp model but they are quite expensive and the only brand that produce one AFAICT. most common units from other brands are in the 20-25 amp range. So far, without scouring out every option on the intarwebs, I have found that ctek offers a nice option in their 140A offroad kit. 140A OFF ROAD (https://www.ctek.com/products/on-board/140a-off-road)
The concept of this kit is that it has a DC-DC charger up to 20 amps in the form of the D250SA and it has the ability to simply hook the mains up to the secondaries through the SMARTPASS 120. The way I currently understand how this works is that under normal circumstances, when the secondaries are empty the smartpass bridges over the D250SA and full current from the alternator will go into the secondaries, charging them with as high a current as they want/can absorb and by the time the voltage has raised and the amperage has dropped to a certain point the D250SA will kick in, taking over the rest of the charging. On paper this sounds to me as the best of both worlds.
Since this unit also has a MPPT controlled solar input that makes life even easier when stationary for a long time. I also figured that since solar is nothing more than a DC voltage source I would bring a switching mode power supply that could provide any voltage inside the input range of the solar input and I could charge the system when stationary and have mains power available. (disconnecting the solar panels at that time of course). A modified HP DL380 server power supply is small, reliable, auto sensing input voltage and can crank out a whopping 80 amps!
Now, I am not sure of redarc or national luna or any of the other manufacturers have similar solutions but in general I wonder what the "best" brand in this business is? ctek is widely seen around here with their 240V chargers and they seem to pretty much own this market, making me believe that since the product is not cheap it must be doing something right. One would assume that this translates well into the mobile solutions. The housing is plastic though and I would think a heat sink type housing would be preferable.
In any case, is there any information out there that my google-fu could not find or does anyone here have any experience on this subject?
Thanks for any input ;)
Cheers,
-P