The question that comes up on every prospecting board, from the old GPAA forum to TreasureNet's drywashing section, is some version of "what battery runs my 12 volt drywasher, and for how long?" The answer starts with a number only you can get: what your machine draws. Here is how to get it, and how to build a battery, solar and fuse setup around it for a claim near Randsburg, in the El Paso Mountains or out past Quartzsite.
Step one: measure the draw
Drywasher makers rarely publish amp draw. Keene's instructions for its 12 volt mini drywasher say only that a small motorcycle battery should run it for about four hours, and suggest a deep-cycle battery for several days. That tells you it is a modest load, not what battery to buy.
Pump makers do publish. Rule lists its 1500 GPH bilge pump at 4 amps at 12 volts and 4.8 amps at 13.6 volts, on a 10 amp fuse, and its 1100 GPH pump at 3.7 and 4.7 amps on a 7.5 amp fuse. The draw rises with voltage. A lithium battery sits around 13.2 to 13.4 volts for most of its charge, so plan on the higher figure.
To measure your own machine:
- A clamp meter that reads DC amps, around the positive lead, with the machine working on real material.
- A SmartShunt between the battery and everything else. It shows the current live in the app and counts the amp-hours used over a whole day at the claim, which is the number you size from.
Step two: size the battery
Multiply amps by hours for each machine. In this example the pump figure is Rule's; the drywasher figure is only an example, so replace it with your own reading.
| Load | Amps | Hours a day | Amp-hours a day |
|---|---|---|---|
| Rule 1500 GPH pump, recirculating | 4.8 | 6 | 29 |
| Drywasher (example only, measure yours) | 6 | 6 | 36 |
| Total | 65 |
Plan on using about 80 percent of a battery's rating; Victron rates the SuperPack's cycle life at 80 percent depth of discharge.
- Victron Lithium SuperPack. A drop-in LiFePO4 battery whose built-in BMS and safety switch disconnect it on over-discharge, overcharge, and low or high temperature. The 60 amp-hour model stores 768 watt-hours, supplies 30 amps continuously and weighs 7.5 kg (about 16.5 lb). The 100 amp-hour model stores 1,280 watt-hours, supplies 100 amps and weighs 10.5 kg (about 23 lb). For the example day, the 100 amp-hour covers it with margin.
- Victron Peak Power Pack. A self-contained pack in 20, 30 and 40 amp-hour sizes (256 to 512 watt-hours, 3.8 to 8.6 kg), with a 30 amp output meant for loads like pumps and a built-in input for a car or solar panel. The 40 amp-hour pack runs the example pump alone for a six-hour day.
- The Eco-Worthy 280 amp-hour stores 3,584 watt-hours. At 68.5 lb it is a trailer or base-camp battery, not one you carry to the wash.
Step three: solar through an MPPT controller
A SmartSolar MPPT 100/30 charges at up to 30 amps, takes up to 440 watts of panel on a 12 volt battery and allows up to 100 volts on the panel side. It stores 46 days of history, so after a week at the claim you can see what the panel actually delivered. Start with one 200 watt panel such as the Renogy 200 W, and add a second if the battery is lower each evening than the one before.
Two things to match:
- Charge current. The 60 amp-hour SuperPack accepts up to 30 amps, which matches the 100/30. The 20 amp-hour SuperPack accepts only 15 amps, so set the controller's charge current to 15.
- The Peak Power Pack's own input accepts 11 to 25 volts and limits the current to 7 amps. Check that the open-circuit voltage on the panel's label is under 25 volts before you connect.
Step four: fuse every circuit
A lithium battery can push a very large current into a short, and a pinched wire on a vibrating drywasher frame is a short waiting to happen. Every positive wire leaving the battery needs a fuse or breaker at the battery end, rated to protect that wire.
- At the battery: a MIDI fuse in a MIDI fuse holder on the main feed, or a 50 amp manual-reset breaker that doubles as an off switch with its push-button trip. Size either to the cable: a 50 amp breaker needs cable rated for 50 amps.
- At each load: its own fuse at the maker's rating. For the Rule 1500 that is 10 amps. For the drywasher, use what its manual or motor label says.
- Protect the connections. Seal the joints at the pump end, and strain-relieve cables where they meet a vibrating frame.
If a fuse keeps blowing, our guide to finding the short walks through it.
Step five: wire gauge for the run
On 12 volts, length is the enemy. Voltage drop is the current times the resistance of the wire, out and back. We aim for no more than about 3 percent, which is under 0.4 volts on a 12.8 volt battery. Drops below are in volts, for stranded copper, counting both wires:
| Load and one-way distance | 14 AWG | 12 AWG | 10 AWG | 8 AWG |
|---|---|---|---|---|
| 5 A, 10 ft | 0.31 | 0.20 | 0.12 | 0.08 |
| 5 A, 25 ft | 0.79 | 0.49 | 0.31 | 0.19 |
| 10 A, 10 ft | 0.63 | 0.40 | 0.25 | 0.16 |
| 10 A, 25 ft | 1.57 | 0.99 | 0.62 | 0.39 |
The lesson: carry the battery to the machine instead of running a long cable. A 5 amp pump 10 feet from the battery is fine on 14 gauge; the same pump 25 feet away wants 10 gauge. Put the panel in the sun and the battery in the shade beside the drywasher. The panel lead runs at a higher voltage, so a long one loses less. A thicker wire never hurts; a fuse bigger than the wire can carry does. Our cable and fuse sizing chart has the heavier sizes.
Keep lithium out of the desert heat
In the desert the limit is heat, not cold. Victron's datasheets set the ceilings:
| Battery | Charge | Discharge |
|---|---|---|
| Lithium SuperPack | 0 to 45°C (32 to 113°F) | minus 20 to 50°C (minus 4 to 122°F) |
| Peak Power Pack | 0 to 40°C (32 to 104°F) | minus 20 to 40°C (minus 4 to 104°F) |
| Lithium Battery Smart | 5 to 50°C (41 to 122°F) | minus 20 to 50°C (minus 4 to 122°F) |
The Peak Power Pack will not charge or discharge at all outside its range. The National Weather Service says that on an 80°F day a closed car reaches 123°F within an hour. That is about 51°C, past every limit in the table. So:
- Keep the battery out of a closed cab and off a black truck bed. Put it in shade with air around it, under the trailer or under a shade rigged above it.
- Mount the MPPT in shade too. It gives full output only up to 40°C.
- Do not store a battery fully charged in a hot shed over summer. Victron rates the SuperPack for a year of full-charge storage at 25°C, but only three months at 40°C.
Trailer bearings for the road out
The roads out to a claim are washboard and rock, and a trailer's wheel bearings take the beating.
- Service them before the season. Our 10-inch Timken kit for 3,500 lb axles uses L68149/L68111 inner and L44649/L44610 outer bearings with a 10-19 double-lip seal. The 12-inch kit for 5,200 to 7,000 lb axles uses 25580/25520 inner and 14125A/14276 outer bearings with a 10-36 seal. Read the numbers off your old bearings before you order.
- Feel each hub at the first stop on the dirt. One much hotter than the others means a bearing or brake problem. Check it before going farther.
- Carry a spare bearing set, seal and grease. A claim is a long way from a parts counter.
Our guides to bearing kits by axle rating and repacking Timken bearings cover the job.
Send us your measured amps and hours and we will suggest a battery and panel to match. Everything ships from Upland, California, and you can collect at the counter on your way out to the desert.