Mercedes

[Mrcoolabah1au]

A friend ask me about a diesel heater for there sprinter is the any problems with wiring or set that she mite need to know I put my own in and had no problem yet would it be just a simple hookup to the battery via a fuse

[SteveW]

In my personal experience, Wayne, and from numerous discussions on various forums, the most common reason for diesel heaters failing to start is low voltage during the start-up process. This is overcome by installing a heavy gauge wire from the battery to the closest available point at the heater unit. In my MH, during the start-up process, the draw is indicated at 11 amps resulting, before I upgraded that wire, in a voltage drop that triggers an error in the unit. So, in answer to your question, make sure the wire from the battery to the heater is of a heavy gauge.

If the house battery is a bit low for whatever reason, having a charging source running during start-up may overcome the low voltage issue.

[Grandad]

Steve, what gauge wire is required for that kind of draw?

Jim

[T1 Terry]

Steve, what gauge wire is required for that kind of draw?

Jim

Depends on the length of the cable run and how many other loads are on that cable run. On its own, 5 mtrs or less, 6mm auto cable (4.3mmsq) will do it but 6mm sq or even 8B&S would be better. If you have a common busbar supply for both the positive and negative, that requires a minimum of 6 B&S cable (13.5mm sq) to supply up to 30 amps over a 5 mtr length, so if you had a number of items to power in the area where the diesel heater will be mounted, probably best to run a pair of 6 B&S cables with a 50 amp fuse in the positive and the negative to the load side of the shunt if you are using one. With the house battery at 12.4v the voltage at the end of the 5 mtr run would be just on 12v under the 30 amp load.
If you double the distance to 10 mtrs using the same 12.4v at the house battery, the maximum current draw drops to 10 amps to keep the voltage above 12v.
As you can see, cable length is an issue, if you want to draw more current over a 10 mtr length, you need heavier cable, 4 B&S or even 2 B&S. As an example, to get the 13v from the start battery to a 40 amp DC to DC charger at better than 11vdc over the 12 mtrs in a Silverado, 2 B&S cable is required, anything smaller and the DC to DC charger simply dropped out due to low voltage after a minute or so, then attempted to restart and the cycle repeated.

T1 Terry

[Grandad]

Thank you Terry. The installation is actually for my neighbour. He's just bought himself a Silverline Jayco and wants to put in a diesel heater.

I, therefore, have no idea at this stage how long the run will be. I have previously mentioned that start-up current is an issue with these things but when I read 12amps that woke me up to why its such an issue.

I'll cut and paste your response to him and then wait and see where is the heater going and where are the batteries, switchboard etc.

Thank you for your time.

Jim

[jon_d]

Jim, Something like this will help.

https://www.project200.com.au/voltage-drop-calculator/

Remember that if you use twin cable, the length has to account for both directions.

Once you work out the length, establish what the lowest operating voltage is. This will be when glowing.

Subtract that from your lowest battery voltage. The answer will be the allowable voltage drop. Plug that into the calculator and work out the minimum cable size. (then go a size or 2 bigger.)

[Mrcoolabah1au]

Wow yes terry was for Nini daughter just bought a sprinter but hav not looked a heaters yes the old saying you get what you pay for I know we spend 1000 on ours five years ago but Chinese you can get for a couple of hundred dollars these day

[T1 Terry]

Wow yes terry was for Nini daughter just bought a sprinter but hav not looked a heaters yes the old saying you get what you pay for I know we spend 1000 on ours five years ago but Chinese you can get for a couple of hundred dollars these day

If you run 1ltr of kero to 9 ltrs of diesel in the heater fuel tank, the chinese heaters work fine. We fitted one in the Hino and Brian (Homeless) has one in his houseboat. The chinese ones can be set by pump rate so you can have them running slow all night rather than switching on and off all the time. That way you can have the motor running so the DC to DC charger is running when you fire up the diesel heater so the battery voltage remains high. Only an issue with lead acid batteries, lithium batteries hold their voltage under load so not an issue.

As far as voltage drop calculations, I use this site quite a bit https://www.calculator.net/voltage-drop ... &x=79&y=18
if you scroll down on the site there is a table that converts many different conductor to AWG (roughly the same as B&S) put in the cable conductor material, expected battery voltage under load, the cable length one way and the expected peak load and it will calculate just how much voltage drop, the percentage and the voltage expected at the end of the cable. It even has a parameter to set the number of conductor runs if you are thinking about running multiple smaller gauge cable run in parallel. Worth playing around with it just to see the effect of multiple small cable runs compared to the larger cable run, a real eye opener. For instance, 3 runs of 6mm auto cable (4.3mmsq) compared to 1 run of 6 B&S cable (13.5mm sq)

T1 Terry

[SteveW]

Steve, what gauge wire is required for that kind of draw?

Jim

Depends on the length of the cable run and how many other loads are on that cable run. On its own, 5 mtrs or less, 6mm auto cable (4.3mmsq) will do it but 6mm sq or even 8B&S would be better. If you have a common busbar supply for both the positive and negative, that requires a minimum of 6 B&S cable (13.5mm sq) to supply up to 30 amps over a 5 mtr length, so if you had a number of items to power in the area where the diesel heater will be mounted, probably best to run a pair of 6 B&S cables with a 50 amp fuse in the positive and the negative to the load side of the shunt if you are using one. With the house battery at 12.4v the voltage at the end of the 5 mtr run would be just on 12v under the 30 amp load.
If you double the distance to 10 mtrs using the same 12.4v at the house battery, the maximum current draw drops to 10 amps to keep the voltage above 12v.
As you can see, cable length is an issue, if you want to draw more current over a 10 mtr length, you need heavier cable, 4 B&S or even 2 B&S. As an example, to get the 13v from the start battery to a 40 amp DC to DC charger at better than 11vdc over the 12 mtrs in a Silverado, 2 B&S cable is required, anything smaller and the DC to DC charger simply dropped out due to low voltage after a minute or so, then attempted to restart and the cycle repeated.

T1 Terry

Thanks for answering that, Terry. I have no idea of the specifics. I just know that I resolved my problem by installing a cable that would supply power to a small city.

[Mrcoolabah1au]

Terry were did you buy your heater or what company or model if we can get the same make as your or Brian’s would be good to know there must a a million brands out there